FANCY THAT (V) : CORRECTION FLUID

CORRECTION FLUID

Correction fluids normally contain trichloroethane.

This is very volatile ( easily changes to a vapour ).

When exposed to the air, this liquid in the correction fluid evaporates leaving the familiar white solid.

FANCY THAT (IV) : ANAESTHETIC

ANAESTHETICS

There are chemicals with sleep-inducing properties. One of the first to be used was ether, C2H5OC2H5, in 1846.

Prior to that date, surgery was a very risky and painful experience. The surgeon had to be very quick in doing the operation and often the patient died from shock!

Laughing gas, nitrogen (I) oxide, N2O was another early anaesthetic, but perhaps the well known of all was chlorofoam, CHCl3. This was first used by Sir James Simpson in 1847.

He used it on women at childbirth. This met with great opposition from various religious groups. However, in 1853, Queen Victoria used it at the birth of Prince Leopold. Since then there has been little religious objection!

Nowadays, other halogenated hydrocarbons are used. Chlorofoam itself is too toxic. Ether is too flammable and dangerous, while laughing gas does not produce a deep sleep.
More substituted hydrocarbons become more inflammable and have more anaesthetic effect. However, the disadvantage is more toxic.

The solution is to use a halogenated ethane molecule!
The most common anaesthetic in operation theatres is
1,1,1-trifluoro-2-chloro-2-bromoethane.

It is more commonly known as fluoethane.

FANCY THAT (III): DECLINE AND DOWNFALL OF ROMAN EMPIRE

'DECLINE AND FALL OF ROMAN EMPIRE’?

In Roman times, the metal lead was common.

It was called plumbum and was used for making containers, various cooking implements and water pipes.

They also store their wine in lead vats and even added it to some wines to improve their flavour!

Lead is poisonous and perhaps, one of the reasons for the ‘decline and downfall’ of the Roman Empire was lead poisoning!

FANCY THAT (II): COSMETICS

COSMETICS

Chemicals which are used for improving the appearance or for beautifying are called cosmetics.
Since very early times, people have been concerned with their appearance and had sought the help of chemicals.

Egyptians, in 5000 B.C., used a fine powder formed of Antimony (Sb), mixed with green copper (II) carbonate (CuCO3) and used as eye-shadow.

In Elizabethan times, iron (II) oxide (Fe2O3) rouge was used to give the face a rugged complexion.

However, in Georgian times, ‘pale faces’ were more in fashion and women used white lead carbonate (PbCO3). As a result many women died as a result of the poisonous nature of lead!

Nowadays, the manufacture of cosmetics is an important industry. Some of these simple salts are used in the cosmetics. Oils and creams are often natural hydrocarbons like carnauba (‘Brazilian Wax’) and paraffin waxes.

FANCY THAT (I) : The HOPE DIAMOND

The ‘HOPE’ Diamond

Diamond is a form of carbon where atoms are held together by covalent bonds in tetrahedral lattice. Each diamond crystal is in fact just one molecule made up of millions of covalently linked carbon atoms.

The ‘HOPE’ Diamond is perhaps the most famous or ‘infamous’ of all diamonds. It weighs 20g and was first used to form the eye of a statue of Sita who was a Hindu goddess. Although its history is varied it hardly brought ‘hope’ to its owners. The story goes that when it was stolen from the statute, the goddess was very angry and made a curse on anybody who owned it.
After being stolen, it was taken to France. Eventually, some hundreds years later, it became part of the French Crown Jewels.

(1) Marie Antionette was believed to have worn the
diamond just before she was executed.

It was then sold to various owners all whom suffered ill luck.

(2) Its English owner, Henry Hope, from whom it got
its name, became bankrupt and died in poverty.

(3) Its Greek owner was killed in a car crash.

(4) A Turkish sultan was overthrown just after he had
acquired it.

(5) American owner, Mrs Evelyn Walsh tragically lost
all of her children in various accidents.

After her death, it was given to the Smithsonian Institute in Washington where it is currently on view.

FANCY THAT !

I came across my secondary school textbook ( from the midst of cobwebs ) with many interesting background reading and fascinating facts!

Some of the background reading are historical while others emphasize the importance of chemicals in modern everyday life.

Hence, i decided to add these into the blog entries so that you will find Chemistry not so CHE-MISERY , CHE-MYSTERY but CHE-MASTERY.

Note:

(1)These articles are adapted from COMPREHENSIVE CHEMISTRY FOR 'O' LEVEL SCIENCE by CHRISTOPHER N PRESCOTT.

(2) These articles are meant for sharing and not meant for any profit-making uses.

Ionic and Covalent Project for 3e1/2 sci chemistry

dear 3e1/2,

these are the compounds that you will have to make during the march holidays!

instructions:
(a) each pupil is to construct your own compounds. No group work. In short, you are responsible for your compounds.

(b) you may want to buy the styrofoam balls together as the shops don't sell one or two. This can help you to save cost.

(c) for large structure, please limit the structure to be 15 cm by 15 cm. This means you don't need so many styrofoam balls. The structure will be small and cute, right?!

(d) just make 1 will do. Don't make extra!

(e) the number refers to the number you have chosen! Eg: (41) diamond meant the person who chose 41 will have to make DIAMOND.

(f) different elements are represented by diffeent colours. Eg: chlorine is green.
please use the appropriate colour.

here are the compounds you have to make:

1. carbon dioxide ( number 1 and 20 )
2. methane ( number 2 and 21 )
3. chlorofoam
4. ethanoic acid ( vinegar )
5. ethanol
6. hydrogen chloride ( number 6 and 22 )
7. hydrogen molecule ( number 7 and 23 )
8. fluorine molecule ( number 8 and 24 )
9. chlorine molecule
10. sodium chloride ( 15 cm by 15 cm ) ( number 10 and 27 )
11. ammonia molecule
12. hydrogen fluoride ( number 12 and 28 )
13. oxygen molecule ( number 13 and 25 )
14. nitrogen molecule ( number 14 and 26 )
15. silicon dioxide ( 15 cm by 15 cm )
16. sodium fluoride ( 15 cm by 15 cm )
17. carbon monoxide
18. sulfur dioxide
19. nitrogen dioxide

and 29. water molecule

that's all, enjoy folks!

this project is for pupils in miss pang's group. Have fun and enjoy!

Explanation For Electrolysis- FYS Pg (4)1-(4)17

Multiple-Choice Question

(2) C
reason: filtration, crystalization and distillation are physical methods. Can only separate mixtures not the individual elements within a compound.

(3) D

reason: elimination method: Aq NaCl and Molten NaCl will have products at electrodes. Bromine is a poor conductor of electricity. Mercury is a metal, just that it exisit in liquid state and it can conduct electricity. So, of course it can conduct electricity. Actually, this question can be seen as a electricity question.

(4) C

reason: cations are attracted to cathode: only option C is cation.

(5) D

reason: this is a typical example of electro-plating, Remeber i taught you to draw cathode on the left? For electro-plating, the object to be plated is on the cathode ( the negative electrode ) while the metal is on the anode ( positive electrode ). Obviously, the electrolyte must be the salt solution of the metal used for plating.

(6) D

reason: the question is trying to ask you what are the possible ions for conc LiCl. So there should be Li+, Cl- (from salt) and H+, OH- ( from water). Cations move towards cathode and anions move towards anode.

BUT, if the question asked about products, then LITHIUM is not discharged. Instead Hydrogen gas. Reason: Lithium is high up in the electro-chemical series as compared to hydrogen!

(7) C

reason: anions attracted to anode. So, no need to crack your brains thinking about the options. All the rest of the options are cations!

(8) B

reason: From the products, X and Y2, you can deduced it is a compound with the formula XY2.

(9)D

reason: Firstly, you need to choose 2 different metals from the reactivity series. And the electrolyte need to be aqueous ( ions ) or molten. But, Cu and Ag is quite a poor example. Why? Because these metals are not much further apart in the reactivity series. The voltage produced will not be larger enough.

(10) B

reason: ions discharged: H+ and Cl-. H+ discharge because Na+ is more difficult to be discharged due to electro-chemical series. Cl- is discharged due to 'concentration effect', so OH- ( from water ) is not discharged instead.

(11) D

reason: cathode gains mass due to copper from anode deposited onto it. Option C is rejected because electrode has weight, should not start from zero.

(12) B

reason: metal ions gain electrons at cathode while non-metal lose electrons at anode.

(13) A

reason: in aqueous copper (II) sulphate. Copper is below hydrogen in the electro-chemical series. So, copper ions will be discharged and copper will be deposited on to the cathode.

(14) B

reason: choose 2 different metals from the reactivity series. Question request for the greatest voltage.

(15) A

reason: (B)-anode is chlorine ( if concentrated; else is O2 ); cathode is hydrogen- NEVER sodium

(C):anode-hydrogen, cathode-sodium

(D):anode- bromine, cathode-lead

(16) A

reason: notice electrode X is connected to positive terminal, so electrode X is anode. Anions are attraced to anode. Cl- ions becomes Cl2 gas. Oxidised.

(17) A

reason: tricky question: the electrode is CARBON. this means all the ions involved are from the ELECTROLYTE. Cu2+ are attraced to cathode while OH- are attraced to anode. So, more of H+ is left behind. Hence solution becomes more acidic. If the question changes to COPPER electrode, then the concentration of CuSO4 and colour remains unchanged!

(18) C

reason: anions attracted to anode. SO42- is not discharged and OH- is discharged instead. This is the concept of 'Selective Discharge'.

(19) A

reason: (B) solution will become acidic. see question 17. For option C, Cl- will be discharged at the anode, H+ will be discharged at the cathode. So, the solution will have more OH- remaining. Hence, it will be alkaline. Option (D): due to the removal of water molecules [ cathode: hydrogen, anode: O2 ], so the concentration of sulfuric acid increases.

(20) B

reason: (A):how can cation forms negative ions. (D):R is below hydrogen, because if it is aqueous, then metal R ions will not be discharged.

(21) A

reason: electrons flow from anode (+) to cathode (-). so, cathode should be Y. Cathode is the more reactive metal.

(22) A

reason: for concentrated or dilute, sodium is NEVER discharged.

(23) C

reason: just focus at cathode-metal; anode-non metal. For option (A), it should be metal ions gaining electrons, and not giving electrons.

(24) B

reason: anode dissolves, all the Cu2+ ions are attracted to cathode hence metal is deposited. electrolyte remains unchanged. IF the electrode is NOT COPPER, example: carbon, then the blue colour of CuSO4 will fade away.

(25) B

'that's all folks!'

ELECTROLYSIS

Molten

Ions attracted to the cathode: Only positive ions ( metal ions )

Ions attracted to the anode: Only negative ions ( non- metal ions )

Cathode: Metal
Anode: Non-metal

Aqueous

Ions attracted to the cathode: Only positive ions
( non-reactive metal ions and hydrogen ions )

Ions attracted to the anode: Only negative ions
( non-reactive metal ions and hydroxide ions
Cathode: Non-reactive metal or Hydrogen gas
Anode: Halogen ( for concentrated )or oxygen ( for dilute cases )

Aqueous ( concentrated / dilute )

Concentrated :
Cathode: non-reactive metal or hydrogen gas
Anode: halogen or oxygen gas.

Dilute
Cathode: non-reactive metal or hydrogen gas
Anode: oxygen gas

If the electrode is reactive, it often dissolves in electrolyte.

Electric Cell ( Simple Cell)

• The further apart the metals are in the reactivity series, the greater the voltage.
• The more reactive metal is placed at cathode. Eg: Zinc at cathode; Copper at anode.
• Any salt solution can be used at electrolyte.

Value Added Series I ( Preparation Of Salts )

Most pupil are puzzled regarding the use of various salt-making methods.

(1) why can't titration be used for all the salts?

(2) Since the first reaction for the topic 'Acids-Bases' introduced 'acids react with REACTIVE metals to give salt and hydrogen gas, can we use this method instead?

Discussion:

There are many methods to make a salt, HOWEVER, we need to see if the method is feasible ( workable).

For the case of 'reactive metals and acids'

Of course, you can use reactive metals and acids to make a salt.

BUT, it will be too dangerous if you are using a REACTIVE metal.

Eg: To make Potassium chloride (KCl), it will be DANGEROUS if you are going to react Potassium with Hydrochloric acid ! Potassium explodes with cold water. [Can You Imagine the reaction of potassium with acids?]

Hence, this method ( acids with reactive metals) can only be used for metals that are moderately reactive! example: magnesium, zinc, etc.

If you want to form Copper(II) sulphate, you cannot use this method because copper is unreactive to acids!
Hence reacting copper(II) oxide/carbonate with acids is the ONLY method!

_____________________________________________________

For the case of 'insoluble oxides/insoluble carbonates with acids'

Ever wonder why it has to be insoluble reagents in the first place?

Back to basics: 'what are acids made of' ?

'An acid is a substance that produces H+ ions when dissolve in water.'

In short, there is water in an acid.

If the oxides and carbonates are soluble in water, then how do you ensure that your acids will be FULLY reacted?

remember in our procedure for heating insoluble oxides/carbonate with acids, step #2

(1) Warm the acid.
(2) add EXCESS insoluble oxides and carbonate and stir to dissolve.
(3) FILTER the mixture ........

If your acids did not REACT with the insoluble oxides/carbonate FULLY, then the acid will contaminate the salt that is formed in the process!

In short, for the usage of heating acids with reactive metals/ insoluble oxide/ insoluble carbonates, the REASONS behind it include:

(1) the oxides /carbonates will be insoluble in water, hence will definitely be able to react with the acids FULLY. Upon complete reaction with acids, all excess metal/insoluble oxides/carbonates will remained and this is an indication that all acids had fully reacted.

(2) the metals used are moderatly reactive and is suitable to react with warm acids.

______________________________________________________

What about 'titration'?

There are a few reasons for the usuage of titration.

The first reason is because the metal is too reactive and using their hydroxides is more appropriate.

Eg: to make sodium nitrate. We cannot use sodium metal as it is far too reactive with acids.
So, we use sodium HYDROXIDE and nitric acid.

In this case, we cannot use heating method as both are soluble and we cannot tell when neutralization takes place.

Hence, for the second reason:

Second reason: If you use soluble oxides and carbonates for the method of heating, one problem you foresee would be unable to know when neutralization occurs. Reason: all the reagents are soluble, you can't tell. ( recall for the case of heating insoluble oxides/carbonates, the reagent is insoluble so you can see when the reagent no longer dissolves in the acid).

But titration is able to tell because of the use of INDICATOR.

Hence, we will be able to know the EXACT amount of alkali needed to neutralize the acid to form the salt when the indicator CHANGES COLOUR.

Please do not state this reason as your answer for 'why titration is used': 'because if we use insoluble oxides/carbonates, it will not be able to pass through the burette' !!!!

I mentioned this point to the class because i wanted you to remember insoluble hydroxides and oxides cannot be used for titration in the LABORATORY. How can an insoluble reagent flow through a burette?

The answer why 'titration is used instead of heating method' because: ** both the reagents are soluble and there is NO INDICATION when neutralization takes place. For titration, indicator can be used to identify the point of neutralization.

Now, is it much clearer?!

2007 EYE PURE CHEM PAPER SOLUTION

SECTION A (MCQ)

1. (B)

2. (C)

3. Redox not covered in sec 3, anyway, answer is (A)

4. (A)

5. given no. of moles of Al2O3 = 1.0 mole
mole ratio of Al2O3:O2 is 2:3
no. of moles of oxygen is 3/2 x 1 = 1.5 moles
mass = mole x Mr of (O2)
= 1.5 x 2(16)
= 48 g (B)

6. chlorine = 2,8,7
when chlorine gains 1 electron to form chloride ion, it becomes 2,8,8 and it has 3 SHELLS
fluorine = 2,7
when fluorine gains 1 electron to form fluoride ion, it becomes 2,8 and it has 2 SHELLS
Magnesium = 2,8,2
when magnesium lose 2 electrons to form magnesium ion, it becomes 2,8 and it has 2 SHELLS
Oxygen = 2,6
when oxygen gains 2 electrons to form oxide ion, it becomes 2,8 and it has 2 SHELLS

so form the largest radius.... which means greater 'circumference' = chlorine
(A)

7. chemical analysis not tested in sec 3, anyway, answer is (B)

8. for graphite, each carbon atom is COVALENT bonded to each other. However, the carbon atoms form a HEXAGON RING. Each ring is connected to another ring by weak VAN DER WAALS ( weak VDW) forces of attraction. Graphite is used as lubricant because its layers can SLIDE over each other. (D)

9. (D)
All these elements are from group 2. All have 2 electrons in the outermost shell.

10. (B)

11. REDOX not teated in sec 3, anyway, answer is (D)

12. option (A) look like group 1 metals , option (B) look like macromolecules. copper is a metal, so it will have HIGH MP, HIGH DENSITY, GOOD ELECTRICAL CONDUCTIVITY (D)

13. (B)

14. empirical formula is the SIMPLEST ratio but MOLECULAR FORMULA is the formula multiply by a factor. In order to calculate the Molecular Formula, we need the relative molecular masses. Eg: the Mr of methane, CH4 is 16 while the Mr of (CH4 )2 is 32. (B)

15. given conc of acid = 1.0 M and mass of CaCO3 = 1.0 g.

no. of moles of CaCO3 = 1/100 = 0.01 mol

mole ratio of HCl: CaCO3 is 2:1

no. of moles of HCl = 0.01 x 2 = 0.02

vol = 0.02 / 1.0 = 0.02 dm3 = 20 cm3 (B)

16. H2SO4 + MgO ---> MgSO4 + H2O ;

H2SO4 + MgCO3 ---> MgSO4 + H2O + CO2

so, in both reactions, water is formed. (C)

17. CHEMICAL ANALYSIS not tested in sec 3, anyway, the answer is (A)

18. (A)

19. option B is very interesting. Covalent compounds are made up by atoms.... but the BETTER word for ' Nature of Particles' should be MOLECULES. Anyway, the formula for option B is wrong too. answer(C)

20. you need knowledge from Chemical Analysis, not tested in sec 3. Anyway, option (D)

21. (C)

22. if X is noble gas, then X,Y,Z is consecutive. So, Y should be in group 1, Z should be group 2.(D)

23. IMPT

Cl2 (g) + 2KBr ( aq) ---> 2KCl (aq) + Br2 (aq) ; colour of KBr and KCl = colourless; but aqueous Br2 = reddish brown

Cl2 (g) + 2KI (aq) ---> 2KCl (aq) + I2 (aq) ; colour of KI and KCl = colourless; but aqueous iodine is dark purple or blue (D)

24. although both potassium (2,8,1) and calcium (2,8, 2) have more electrons than aluminium ( 2,8,3 ). But aluminium donates MORE electrons into the sea : Al (s) ---> Al3+ (aq) + 3e- so answer (A)

25. total no. of electrons share = no. of BONDS in the molecule: 8 bonds x 2 e- = 16 e- answer (C)

26. (C) reason: the formula should be XO

27. when ammnium chloride is heated, it forms ammonia gas and hydrogen chloride gas: NH4Cl (s) ---> NH3 (g) + HCl (g) option (B)

28. notice the no. of protons and elecytrons for both X and Y is not equal! by right, in an neutral atom, X should have 4 electrons and 4 protons while Y should have 20 protons and 20 electrons. So this shows that both X and Y lose electrons. Only Metals lose electrons. Hence option (D)

29. R has 4 electrons involved in bonding. Hence R is in group 4. option (B)

30. given X contains acid ---> from universal indicator, X should have a pH less than 7. As for the reaction between KI and Pb(NO3)2, it will give a yellow ppt of PbI2 :

2 KI + Pb(NO3)2 ---> 2 KNO3 + PbI2 ( PbI2 is yellow ) option (A)

SECTION B (STRUCTURED )

1a) ammonia b) Chlorine
c) Lead (II) oxide
d) Magnesium chloride
e) Brass

2(a) chemical analysis Not tested in sec 3

a) zinc hydroxide / white / soluble in excess giving colourless solution. [1.5]
iron(II) hydroxide / dark green / insoluble in excess [1.5]

b) (i) Magnesium, sodium, caesium and beryllium [½]
(ii) Sodium, aluminium, magnesium and chlorine [½]
(iii) Hydrogen, sodium and caesium [½]
(iv) Carbon and tin [½]

3 a) ionic / ionic / covalent / covalent / covalent / covalent [2]
b) giant / giant / simple molecular [2]

c) MgO is ionic and giant structure is strong and stable, hence it has higher
melting point. whereas the SO3 is covalent bonding and a simple
molecular structure. [2]

d) Na2O(s) + H2O(l) ---> 2NaOH(aq) [1]
SO3(g) + H2O (l) ---> H2SO4(aq) [1]

4 ( chemical analysis not tested in sec 3 )
a) A Copper(II) carbonate [1]
B Carbon dioxide [1]
C Copper(II) chloride [1]
D Silver chloride [1]
E Copper(II) nitrate [1]

b) CuCO3 (s) + 2HCl(aq) ---> CuCl2(aq) +CO2(g)+ H2O(l)
CuCO3(s) + 2H+ ---> Cu2+(aq) +CO2(g)+ H2O(l) [2]

5 (oxidation and reduxtion not tested in sec 3)
a) i) +6 ii) +3 [2]
b) Aluminium [1]
c) gain of oxygen or increase in oxidation state [1]
d) Cr2O3 is oxidizing agent. [1]

6 a) i) yes, they all have similar formulae
ii) yes, peroxides and super oxides are likely formed at the
elements below the group.
b) O- , O2-
c) i) H+(aq) + OH-(aq) ---> H2O(l)
ii) 2I-(aq) + Cl2(g) ---> 2Cl-(aq) + I2(s)
iii) Zn(s) + 2H+(aq) ---> Zn2+(aq) + H2(g)

7 a) i. P6O4 ii. P3O2 [2]
b) It is an non-metal oxide
it is covalent bonding
it has no free electron and no mobile ions when molten. [3]

SECTION C (FREE RESPONSE)

1 a) i) Mg(s) + S(s) ---> MgS(s) [1]

iii) Mg :24 + S: 32 à MgS : 56
3 4
12g 16g

Actual: 16g of Mg is used, Sulphur will be used up first in the reaction. [1]
Hence sulphur is the limiting agent. [1]

iv) S MgS
32 56
16g 28g 28g of MgS formed [1]
b) CaCO3 (s) + H2SO4(aq) à CO2(g) + CaSO4(s) + H2O (l) [1]
100 24000
y 1200 [1]
y = 100 x 1200/ 24000
= 5 g (CaCO3 is reacted) [1]

Percentage purity = 5/6 x 100%
= 83.3 % [1]

2 a) i) % of Na = 12.5/45 x 100%
= 27.8%

ii) Na H C O

27.8 12. 14.3 56.7

27.8 1.2 14.3 56.7
23 1 12 16

1.2 1.2 1.19 3.54

1 1 1 3

Empirical formula = NaHCO3
iii) Mr of empirical formula (NaHCO3 )= 23+1+12+ 16x3 = 84
Mr of molecular of NaHCO3 =84
n = 84/84 = 1, Hence, molecular formula = NaHCO3 [1]

b) i) NaHCO3(aq) + HCl à NaCl (aq) + CO2(g) [1]
ii) 84 24
45 x

Conc. Of HCl = 91.3/36.5
= 2.5 mol/dm3
mol of HCl used = 280/1000 x 2.5
= 0.7 mol
hence, vol of CO2 produced = 0.7 x 24dm3
= 16.8 dm3

c) [ chemical analysis, not in syllabus ]
Add equal volume of sodium hydroxide and small spatula of
aluminium powder into a sample solution. [1]
Warm till the aluminium dissolves. [1]
Effervescence and pungent smell gas produced turns red litmus
paper blue. [1]

3 a) methyl orange [1]
b) 22.8 cm3 21.5 cm3 28.7 cm3 [1]
√ √ [1]
c) 25.0 cm3 [1]
d) H2SO4 + 2NaOH à Na2SO4 + 2H2O [1]
e) average of sulphuric acid used = (22.8 + 21.5) / 2 = 22.2 cm3 [1]

mol of H2SO4 / mol of NaOH = 1 / 2
mol of H2SO4 = ½ x mol of NaOH
0.05 x 22.2/1000 = ½ x 25/1000 x mol of NaOH
mol of NaOH = 0.0444 mol/dm3

Disclaimer: only the MCQ answers are from miss pang, answers from section B and C are done by another teacher. Miss Pang is not responsible for the accuracy of the answers!

Old Blog Revived!

Hey pupils,

I was so forgetful and I didnt remember my password and my poor blog was not manned.

I was so shocked that I noticed messages tagged on the C-Box that had vulgarities and profanities on it.

Please do not do such a thing, for if I want to pursue this issue, I can.

I welcome any of you to raise questions again!!!!

Sanny, you asked if you are not with me anymore, could you still ask me questions. Answer is YES!!!

Thank you Mr Chan for helping me to answer the questions . . . I really welcome you to visit the blog.

The Chronicles Of 3 Little Pigs!

Another chronicle written by my sister.

Enjoy!

******************************************************************

The wolf which attacked the three little pigs had died from the fall off the chimney, but the story, or the chronicle of the 3 little pigs did not quite end there.

That fatal accident had created a huge stir-up and earned raved reports from the press. The proud wolves found that snub hard to stomach, and that incident had, to a certain extent, affected the operation of the local Bee Hiang Hiang store. Thanks-giving was round the corner, yet there was hardly any pig caught to serve as the main ingredient. The scarcity of pork made pessimists in the Wolf-Village turn to other food-alternatives, and many lived on a vegetarian diet.

This food crisis drove everyone in the Wolf-Village to desperation, and the wish for a sumptuous meal during the festive season brought the brains of Wolf-Village together, to stage a comeback. The review committee hired the well-learned Professor Wolff to conduct an independent review of that fatal accident. Analysis showed that the huff-puff method passed down from several generations before was obsolete and was no longer effective in toppling the brick houses built by the pigs. The R &D done by the pigs in Housing Development Authority (HDA) was indeed remarkable, and the suggestion made by Professor Wolff to solve this problem was to burn the brick house and force the pigs out of their sty.
He calculated that the brick house needed at least 100 000 kJ of energy to be completely engulf in fumes, and complete combustion of 1 mole of coal released approximately 100kJ of energy. The molecular mass of this special coal, coal W, designed by Professor Wolff, was 800.00g. Detailed calculations showed that 1000 mole of coal W was needed, which would weigh 6.023 x 10 23 x 800g x 1000 = 4.8184x10 29g.

As soon as the required amount of coal W was produced, everyone from the Wolf Village was mobilized to transport the coal. The Huff-Puff method was abandoned, but the transportation left everyone huffing and puffing. The target sty for the first attack to be launched was the sty built by the 3 little pigs who were responsible the many months of distress suffered by villagers in the Wolf Village.

It was by no means an accident that the 3 little pigs survived. Although the previous ordeal was a victory for them, they did not rest on their laurels but worked on improving the safety aspects of their estate. They knew that although their houses were “huff-puff-proof”, they were nevertheless not fire-proof and would engulf in flames should a fire break out.

The smart 3 little pigs had long designed a hot air balloon that could support the mass of the 3 of them should there be a fire. Careful calculations and experimentation showed that in order for the hot air balloon to support their weight as well as the necessary amount of coal for continual burning, 2400dm3 per second of hot air was needed. One mole of a specially-designed, fuel efficient coal, coal P could provide 1 mole of hot air, which is 24dm3 upon combustion.

Thus in order for the 3 of them to stay in the air for 1 hour, 60 x 60 x 100 = 360000 mole of coal P was necessary. The molecular mass of coal P is 600.00g. Thus the total mass of coal P required was 600 x 360000 = 216000000g. Wow!!!


The time was ripe when Professor Wolff saw strong wind blowing in the direction of Pansy Village, the village where the 3 little pigs stayed.

“Comrades! Start the fire! ” ordered Professor Wolff, as he sat a distance away from that brick house, sipping red wine, waiting for succulent pork to be served soon. Professor Wolff choked on his drink when he saw the roof of the brick house shoot-open, and the 3 little pigs flying-off with a smirk on their face in the hot air balloon! The sudden attack had failed to restore the reputation of the wolves being the most-capable animals in PW town (consisting of only Pansy and Wolf Village), but further undermines the standing of Wolf Village in PW town. My goodness!!!

It appeared that the coming Thanks Giving dinner in Wolf Village had no choice but to serve many salad dishes, and there was a real prospect that a vegetarian diet might stay for good.

by: xue yin ( another miss pang )

My sister and shana inspired me ( not shana's fault, so please don't blame her ) to offer one of my chem classes on a written assignment ' The Chronicles Of The Mole '.

Being a weak english person, I try my best to write an event regarding the mole.

Enjoy...

*******************************************************

Huai Ren was waiting outside the A & E. The police had notified him of Jenny’s accident.
After the operation, he was informed by the surgeon that Jenny had escaped death and would be transferred to intensive care unit.
Huai Ren entered the room. Accordingly, Jenny had sprained her neck and fractured her ribs due to the crash. The fractured ribs pierced through bronchiole and the doctor had to give her pain killers through injections. Jenny’s arms suffered from deep cuts due to the broken windscreen.
Huai Ren walked towards Jenny and lamented at her misfortunes.
She was not like this before, at least 1 year ago.
Jenny had suffered from post natal syndrome ; after her maternity leave, she needed to deal with the day-to-day operations of the company and these had proven too much for her. Her dad had suggested Huai Ren to take over the CEO position so as to lessen her duties. Recently, the company was faced with problems of cash flow. A large sum of funds was trapped in an acquisition project of a promising company’s shares.
Jenny insisted Huai Ren had misappropriated the company’s funds.
Huai Ren left the ward for he knew if she woke up, he would not be the person Jenny would want to see.
After visiting hours, someone entered Jenny’s ward.
He took out a syringe and held Jenny’s arm. With a swift movement, the hollow needle pierced through the skin and into the vein. 2.25mg/dm3 of Warfarin was injected into the bloodstream via the vein. He had done his calculations well. For every 13 kg of body weight, there is an equivalent amount of 1 litres of blood. So, Jenny would have around 4 litres of blood if she weighed 50 kg.
The maximum concentration of warfarin that her body could take should not exceed 5.0 mg per body of blood. Since concentration can be defined as amount of substance dissolved in 1 L, which is 5.0/ 4 = 1.25 mg/dm3. An overdose of warfarin will lead to bleed profusely as blood will not clot.
He could visualise the shock on the nurses’ faces when they saw her bleeding while doing their rounds the next morning. Blood would be oozing non stop from her cuts.

*******************************************************

ms pang:)

2005 SciChemistry MCQ

2005 MCQ
1) A * explanation *less dense means light, so we use the upward dispalcement method( see notes blog )
so, reject option B. B is for heavy gases ( downward displacement method )
option C is for insoluble gases.
2) C
* explanation *
when particles at 50'C ( liquid ) becomes 120'C ( gases ),the energy of the particles increases, the spacing between the particles becomes far apart and hence the attractive forces between the particles decreases.
3) C* explanation *81 is nucleon number ( proton + neutrons ) / atomic mass37 is proton number ( proton = electron )therefore, 81-37= 44 neutrons.
4) C* explanation *Element X has a valency of +1Element Y has a valency of -2
therefore, when you use the criss-cross method, the formula is X2Y1
5) D

* explanation *

Element Q has 4 valence electrons

---> group 4 ( since number of valece electrons = group number )

Hydrogen and chlorine are non-metals.

So, non-metal & non-metal = covalent compound.

properties of covalent compound = low melting point ( see notes blog )

6) D
* explanation *look at what is given to you: you have 0.3 moles of C3H8.to find volume of gaseous productsso, which is the product they want? from the question, there is CO2 and H2O?answer: look at the state symbols, CO2 is in (g) state!!!mole ratio of C3H8 : CO2 is 1: 3no. of moles ofC3H8 = 0.1,1unit = 0.1,3 units = 0.1X 3 = 0.3 moles(please dont be careless and choose option B!! we have only found CO2's mole, the question wants VOLUME ) so,using P.K.X fav sentence: 1 mole of any gas = 24 dm3 at r.t.p,so, 0.3 mole = 0.3 X 24 = 7.2 dm3
7) B
* explanation *
during the process of neutralization, the temperature will increase ( see notes blog )that is why options C and D are out!now, when neutralization finishes, the ecess alkali added will make the temperature of the solution back to room temperature. Hence a decreasing gradient.
8) B
option A: when a more concentrated acid is used, the gradient of the graph will be steeper instead of gentle because the rate of reaction is faster.option C: when fewer amounts of reactant is used, the amount of CO2 produced will be less. So, it will not reached the same level as graph 1.option D: when powdered reactant is used, speed of reaction should increase, instead of decrease!

9) B
* explanation *

option A, D are out because all potassium salts are soluble!

remember the K-N-N-Na theory.

option C is out. Potassium sulphate is a salt, not a base.

answer is potassium carbonate neutralises the acid.

10) C

* explanation *

when halogen is Y added to X and Z, there is no reaction, this means that Y is the least reactive.

so, down the group of 7, reactivity decreases, so, Br- is the least reactive.

so, Y = Br-

if X can displace Y and Z, then X is the most reactive.

so, X = Cl-

11) B
12) D
* explanation *option A: coke is not used to oxidised slag!! coke is used to burn to give carbon dioxide and carbon monoxide!

option B: limestone is used to decomposed to form calcium oxide and carbon dioxide.

the calcium oxide is used to neutralise slag.

option C: molten iron is heavier, so it is at the bottom, and not floats on the slag!

13) D

14) B

15) A ( see textbook for the uses of cracking )

16) A

* explanantion *

in the complete combustion of organic compounds, only carbon dioxide and water are formed.

17) D

18) C

* explanation *

only compounds with C=C bonds will decolourise aqueous brmine.

other C= structure will not decompose aqueous bromine.

19) C ( see textbook )

20) D* explanation *polyester = many units of ester group.
Terylene contains ester linkage.Nylon contains amide linkage.Poly(ethene) contains many units of ethene .Protein contains amide linkage.

Remedial Timeslots for 3E2 Pure Chemistry

Dear 3E2,

These are the timeslots for our InTeNsIvE TrAiNiNg PrOgRaMmE.

Please bring your stationaries, Five Year Series and Chemistry Textbook and File.
Venue: 3E2 classroom

16/06/08

Elements, Mixture and Compounds

Time: 11.15am to 12.45 pm

17/06/08

Structure of solids, Bonding

Time: 9am to 12 pm

18/06/08

Balancing Equations

Time: 2pm to 4 pm

Note:

I am having lessons for 4a,4e and 5a on 16th and 18th, so i cannot schedule your 'programme' eariler.

The lesson will end early if we finish our planned programme. Please do not be late for lessons.

miss pang :)

Reply to Germaine's Question : Is hydrogen a metal or non-metal

GERMAINE: hydrogen is metal or non metal?

My Reply: Hydrogen is a non-metal! However, it loses electrons to form H+ ions. ( so, i guess that is why Germaine will question its identity ).
The reason is it is more stable.

However, in tertiary levels ( JCs / Polys/Uni ), Hydrogen can also gain electrons, which is H- ions ( hydride ). There exist many metal compounds in which metal bonds with hydrogen and hydrogen gains ELECTRONS from metals. Such compounds are known as Metal Hydrides!

Thankfully, not in your syllabus!

ms pang :)

Reply to Mark's Question

Mark asked: ' i thought carbon-carbon is a quadriplet bond? and is in diamond, which is a giant colvent bonding. '

My reply to HJ's question was ' Are there any COMPOUNDS with carbon - carbon quadruple bond. '

Your comment was for diamond.

Firstly, diamond is made up by many many CARBON atoms joined together through covalent bonding. It DOES NOT have any other elements ( only carbon atoms ) in the composition of diamond. So, it is not the same as HJ's question as diamond is an element, not a compound.

Secondly, Quadruple bonds means one element shares 4 electrons with another element, and vice versa. Total 8 electrons within the 4 bonds.

For diamond, each carbon atom forms only one bond with another carbon atom. Which means each carbon atom forms 4 single bonds with 4 other carbon atoms!

ms pang:)
p/s: I am not taking a break.... was busy with the preparation for philippine's trip!

Reply to HJ's Question: Are there any compounds with quadriplet bond?

Hj: ms pang,is there such thing as quadriplet bond?

my reply: Should not have at your level. The maximum number of bonds between two atoms is only triple bond. eg:

dot and cross structure of nitrogen molecule

Structural formula ( read as ' N triple bond N ' )

As for the presences of quadruple bond... yes.... mainly in transition metal. Eg: Chromium.

I double check with miss wendy heng regarding HJ's question and I almost forgotten that in uni, we did manage to draw quadruple bond!!! ( many thanks to her ).

Just for your information... not in your secondary syllabus.....

chromium acetate

I edited this diagram so that you can see the quadruple bond easier... the original diagram is blur and show 5 bonds due to low resolutions.

I didnt draw these structures, i got it from this website:

(1) http://www.gcsescience.com/a25.htm ( nirogen molecule )

(2) wwwchem.uwimona.edu.jm:1104/courses/chromium.html ( chromium acetate )

p/s: is KING = Gareth? .. i assume HJ as 'hong jie'

ms pang :)

Chemistry Remedial For 4E1/4 Sci-Chemistry and 3E2 Pure Chemistry

Dear 4E1/4 and 3E2

In view of the upcoming MYE ( mid year exam )2008. There will be remedials for these days:

4E1/4 ( 3e2, be patient. Your timeslot is written below 4E .. so read on)

Our remedial will resumes from this saturday ( 26 april 08 ) onwards. Reason for cancelling the remedial on 19 april is due to real busy day of mine from morning.

The remedial will be conducted at only 1 slot: 10 am till 11.30am at AVA.

Target audience... 60 pax of you.

Topic: Chemical Analysis ( Cation/Anion)

This is a SUPER difficult and important topic ; this topic worths at least [5 mks ] in exam EVER YEAR without fail.

Since this topic needs alot of practice... we will continue with more practise for chemical analysis on 3 May 08. Same time, same venue.

You are advise to turn up for both sessions so you can have maximum exposure to this topic. Should you choose to attend only 1 of the above sessions, you may feel lost as practise is a continuation process.

3E2

Please inform your parents you have remedial.

Session 1- Revision: Structure of Atoms & Bonding ( 26 april 08 / 8.30-9.30/AVA )

Session 2- Revision: Formulas & Balancing Equation ( 3 may 08 / 8.30-9.30/AVA )

I will be going through FYS on 30 April. So all of you please stay back after your last paper. Have your lunch before our revision.

For administration purpose and monitoring of results, these are the pupils who attend sat remedial:

22 march 08

anas, michael, jason, yazid, cheryl, natasha, cheng hong, ronald

29 march 08

jessica, weifen, jolene, farid, anas, michael, jason, cheng hong, natasha, cheryl, jeffery

05 march 08

farid, jeffery, cheng hong, david, michael, anas, meiling, jolene, natasha, cheryl, jia min, yan ne, pei yee, weifen

__________________________________________________

The preparation for O-Level Exam is similarly to preparing for a Marathon.....

Before you run, you need to warm up. However, with 'conditioning your body' for the run, it is impossible to have a marathon because it may lead to sprains and you may not even complete the run!!!

Slow and steady wins the race.

cheers,

ms pang:)

Reply To Mark's Question: Why must we have UV light for free radical substitution.

My reply:

Firstly to have chlorine radical, i need to get it from chlorine molecule....

So, I need a minimum energy to break up my chlorine molecule to get chlorine radical....

ms pang :)

Reply To Mark's Question: Nobel Gases Group 8 or Group 18

Mark asked: ms pang, why is it we learn that nobel gas are grp 8 metals when they are grup 18? source: http://en.wikipedia.org/wiki/Noble_gases

my reply:

Indeed an interesting question!!!

But, let me make an amendment to your question...

Noble Gases are group X or group 0 non-metals.... not METALS.

Anyway, why wikipedia says group 18?

This is a new TERMINOLOGY....

Most scientist wanted to fit Transitions Metal into groups too... recall in our periodic table, transition metals are catagorise as a 'rectangular block' with no group......

So, after adding the transitions metal, we will have 18 groups hence noble gases become group 18!!!

Nonetheless, facts from websites cannot be trusted wholesomely..... unless it is some education (edu) or government (gov) websites..... such websites have more credibility.

ms pang :)

Reply To Hao Eng's Question: Does SO2 have double bonds?

Hao Eng asked: Does SO2 have double bonds between them?

My reply: Yes!

Both sulphur and oxygen has 6 electrons in their outermost shell. In order to have 8 electrons for oxygen atoms (octet structure ), sulphur needs to share 2 electrons with EACH oxygen.

Alas, then sulphur will have 10 electrons!!! Which is not octet structure!

In tertiary levels ( jc/poly/uni), sulphur can 'expand octet' which is a term refering to an atom that has more than 8 electrons in its outermost shell ...

A piece of good news. You are not expected to draw this structure for O-level Exam.....

ms pang :)

p/s: i didnt draw this diagram, i got it from this website:

http://www.btinternet.com/~chemistry.diagrams/molecular_diagrams.htm

Reply To Qi Ying's Question: How many bonds does chlorine and hydrogen have?

Qi Ying asked: how many bonds does chlorine and hydrogen have?

my reply:

Chlorine and hydrogen does not have bonds. The question 'should be' how many electrons can the hydrogen and chlorine used for bonding.

Chlorine is in Group 7 so it has 7 electrons.
If it combines with a metal group, then it can only accept 1 electron from the metal. ( so that add up to be 8 electrons )

If it combines with a non-metal group, then it can share only 1 electron from the non-metal thus forming 8 electrons too.

In this case, if chlorine combines with hydrogen to form hydrogen chloride, then only 1 bond is formed between hydrogen and chlorine.

ms pang :)

Groupings for March Holiday's Project

Dear all,

please double check your grouping,

Group 1: Ionic compound (NaCl, MgCl2)

Gareth
Mikhail
Chong cheng
Hong jie
Naufal

Group 2: Ionic Compound (NaF, CaCl2)

Jeremy
Yan seng
Nadi
Jovin

Group 3: Simple covalent molecules (H2O, CO2,CH4, O2,H2,Cl2, HCl, NH3, CO, C2H4)

June
Qian hui
Eileen
Bao yuan
Jun ling

Group 4: Simple covalent molecules (H2O,CO2,CH4,O2,H2,Cl2, HCl, SO2, CH3COOH)

Shi min
Candi
Fiona
Qi ying
Hao eng

Group 5: Macromolecules (diamond, graphite)

Jerry
Hung yih
Zi jun
Jian Qiang
Kevin

Group 6: Macromolecules (silicon dioxide, graphite)

nil

attention to shana, nicole, zhi ying, shermaine, celin and sheng lin you girls have not sign up for your topic!!!

Reply To Mark's Question: Is there such a substance CaClOH?

Mark asked: 'just to check, is there such thing as CaClOH ?'

My reply: Yes!!!! But not in your syllabus.

In the reaction of HCl and limestone under furnace and boiler conditions, CaClOH is an INTERMEDIATE product.

'intermediate product' means, the reaction produce this product and this product (known as intermediate product) will further react or continue in the reaction to form the final product.

If not, under NORMAL conditions, HCl will react with CaCO3 ( limestone) to form carbon dioxide, calcium chloride and water.

ms pang:)

Saturday Revision Topics: Group Properties

Dear all,

Some of you are not required to attend the saturday's remedial due to your better chemistry results. You may get a copy of the extra exercises ( 1st remedial- mole concept; 2nd remedial: Group Properties) from me every week on monday!

However, answers are not provided. Please complete on your own before seeking Mrs Jaya or myself for help.

As for the pupils who have been attending the remedials regularly, please continue to do so.
It is easier to revise and complete the exercises with help rather than struggling to complete it on your own! In addition, you can clarify your doubts!

Apologies for the cancellation of 2 slots due to my revision for 3A3 today.

The attendance is as follows:

Michael, Yazid, Cheryl and Natasha ( 10-11am)
Cheng Hong, Yanne, Acslyn [ i spelt correctly:) ], Geok Teng ( 11-12pm)

Amendment To 4E1/4E4 Science Chemistry Common Test Topics

Dear 4E1/4E4,

There are a total of 5 topics for your common test on 20th feb.

The topics are:

(1) Chemical Bonding

(2) Mole concept

(3) Periodic Table and Group Properties

(4) Metals

(5) Redox ( reduction and oxidation )

Sorry for the amendment :(

Time slots for next saturday remedial 16 Feb 2008

Dear 4E1/4E4 pupils,

Attendance is COMPLUSORY for pupils who failed the metal test or the mole concept test!!

i will be revising metals (especially displacement reactions) and simple redox ( reduction and oxidation ) on 16 Feb.

These are the time slots:

(1) 8.30 am-9.30 am
(2) 9.45 am-10.45 am
(3) 11.oo am- 12.00 pm

Note:

(A) Maximum pupils per group will be 4.
(B) Please bring along textbook and Five Year Series.
(C) If all the slots are filled, you have to see me anyday from Monday-Thursday.

For administration purposes:
These are the pupils who attend the mole concept revision on 09/02/08.

-acsyln, ronald, jolene
-keith, cheryl , natasha
-cheng hong, geok teng

Latest News For Sec 5 Normal Academic Science Chemistry Common Test on Week 7 / 8

The topics tested for Science Chemistry Common Test (5A) on week 7/8 are as follows:

(1) Bonding ( ionic, covalent and their properties )

(2) Mole concept

(3) Metals ( properities of metals, extraction of metals, uses of metals and recycling )

(4) simple oxidation and reduction

(5) Periodic Table

Please pass this information around:)

Latest News For Normal Academic Science Chemistry Common Test on Week 7 / 8

The topics tested for Science Chemistry Common Test (4A1-4A3) on week 7/8 are as follows:


(1) ionic and covalent bonding



(2) mole concept: calculating reacting equations



(3) acids, bases and salts ( including oxides- acidic, basic and amphoteric )

Please pass this information around:)

Latest news for chemistry common test on week 7/8

The topics tested for Science Chemistry Common Test (4E1/4E4) on week 7/8 are as follows:

(1) ionic and covalent bonding

(2) group properties [ group 1,7,8 ]

(3) metals [ properties of metals, reactivity series of metals, extractions (esp. iron ), recycling ]

(4) oxidation and reduction

Note: Five year series will be available to you guys on thursday 31st jan 08, so you guys will be able to practice the questions. Will keep you inform what questions to practice.

Pass this info to your friends/classmates:)

Some Tips for Qualitative Analysis

A lot of pupils fare badly for Qualitative Analysis.

Students are unable to choose the appropriate test for identifying the gas evolved.

Typical Scenario:
When a gas evolved from a reaction, pupils used All the various test to identify the unknown gas.
Before the correct test can be used to test for the unknown gas, the reaction stopped to produce any gas!!!!

So how?!?

You can deduce the identity of a gas ( before actually testing ) by:

*** 1.The reactions that produced the gas.

2.The odour of the gas.

3.The colour of the gas, (whereby in your syllabus), chlorine is yellowish green.

For hydrogen gas

the reagents used will surely be acids and metal strips...

if you did not used any shiny powder ( probably metals ) or shiny strips, then the test for hydrogen is NOT NECESSARY because hydrogen gas will never be produce when the reagents are not acids and metals!!! so, please do not test with burning/lighted splints.

For carbon dioxide gas

carbon dioxide only evolved when you heat a carbonate or you react an acid with a carbonate. So, if you are not using a dull powder (or dull solids) then no need to test for carbon dioxide gas!!

For oxygen gas

oxygen gas will not be produced from acid-base/acids-metal/acids-carbonate reactions!!!!

oxygen gas reactions can be very tricky....

because there are a few reactions that produce oxygen gas.

Eg- adding manganese oxide to hydrogen peroxide and heating nitrates.

Pupils always expect the glowing splint to rekindle BRIGHTLY... however, in most reactions, this does not happen.

The reason is simple.... the amount of oxygen gas produced from your 1-heap spatula and 2cm3 of solvent is not enough to produce alot of oxygen gas!!!! Should you observe a slight glow/brightens, you can safely deduce the unknown gas as oxygen.

Lastly pupils need to know HOW TO CONCENTRATE GASES

Pupils need to use their thumb to cover the openng of the test-tube to 'concentrate' the gas.

This is to ensure the gases will be enough to create a clearer result. Most of the time, pupils failed to observe the result because the gas that travels from the reacting mixture to the opening of the test-tube is too little.

hope that you find this useful!

Studying Strategies :)

Ever wonder why you STILL score a C5-6 grade even though you do school work/ studied at home/pay attention during lessons?

seems no justice ?!?

Well, justice can prevail ... read more to find out......

(1) Know what is the most/more important ideas of the topic

It is no use memorising the whole topic......
there are times pupils memorised chapters/practise a particular concept and spend 1 week for revision of a topic where it will only be of a weightage of less than 3 marks in exam!!!

the next question you would ask ," but we don't know what is important for the exams? "

then, you have to (1) ask the teachers; (2) see which questions are usually/ frequently tested in the past year papers!!!

(2) Know the mark allocation of the question

Most pupils waste their time by writing more than 4 sentences for a 1 mark question!!!

Pupils need to know that [1 mark] is approxiamtely 1.5 minutes.

Hence, every sentence you write will be equivalent to almost [ 1/2 mark ]. In other words, pupils should not have any 'waste move'. again, if pupils do not know the mark allocation for the question, please seek teachers advise!!!!

(3) Know how to identify the question to the chapter and to link common answers to the question

This is an extremely important strategy!!!!!

Usually, pupils failed to identify the question to the relevant chapter. As such, they have difficulty in suggesting reasonable answers.

Example,

sodium chloride and chlorine gas are substances of chloride. Explain why sodium chloride has high melting point while chlorine gas has a low melting point.

Suggested answers from pupils :

sodium is a metal and chlorine is a non-metal, hence sodium chloride is high melting point; chlorine gas is a non-metal, hence low melting point.

Does this solution make sense?!?

Firstly, this solution does not need any information from the topic-bonding. Any secondary 1/2 will be able to identify whether sodium is a metal or not from the periodic table!!!!

Strategy: When a pupil sees this question. The pupil MUST identify the topic which is bonding.
From bonding, try to recall the words-' ionic bonding' and 'covalent bonding'.... ( no other chapters talks about bonding, so it is very obvious )
from ionic bonding-- try to link it to electrostatic forces of attraction while covalent bonding, link it to weak intermolecular forces of attraction.

Generally, teachers will inform pupils to memorise the reason for high melting point. The sentence goes like this, " sodium chloride is an ionic compound, a large amount of energy is needed to overcome the strong forces of attraction between oppositely charged ions, hence high melting point. On the other hand, chlorine gas is a covalent molecule. A small amount of energy is needed to overcome the weak intermolecular forces of attraction between the molecules. Hence low melting point. "

If you can remember the topic correctly, should be able to ring a bell and will be able to write a few sentences from the 'standard answers by teachers'......

that's all for my sharing :)

May the force be with you

Replying Ronald's Question: How do we know the valencies of ions?

Ronald asked:

Ms Pang, hw u noe whether the Element electron charge is -2, -1, +1 or +2

My reply:

an ion ( not element ) will have a charge of minus or plus depends whether it is a metal or non-metal.
For metal, it tends to form ions of charge +1, +2, +3 ( cations- lose electrons )
For non-metal, it tends to form ions of charge -1,-2 ( anions - gain electrons )

ms pang:)

ALCOHOL

Formula of alcohol :

CnH2n+1OH

Nomenclature

all alkanes begin with the prefix as mentioned below and ending with -ol

( 1 carbon atom) methan-

( 2 carbon atoms ) ethan-

( 3 carbon atoms ) propan-

( 4 carbon atoms ) butan-

( 5 carbon atoms ) pentan-

( 6 carbon atoms ) hexan-

( 7 carbon atoms ) heptan-

( 8 carbon atoms ) octan -

( 9 carbon atoms ) nonan-

(10 carbon atoms ) decan-

Properties of alkene

1) Combustion

Burns in plentify supply of air, it produces carbon dioxide and water.If INCOMPLETE COMBUSTION, it gives soot, carbon monoxide, carbon dioxide and water.

2) Oxidation

(a) ethanol oxidised to ethanoic acid by warming with acidified potassium dichromate.
(b) ethanol can be oxidised to ethanoic acid using air by the bacteria in the air.

3) Formation of esters

Alcohol reacts with carboxylic acids in the presence of a few drops of concentrated sulphuricacid as a catalyst to form esters and water.

ALKANES

Formula of Alkane :

CnH2n+2

Nomenclature ( Naming )

all alkanes begin with the prefix as mentioned below and ending with -ane

(1 carbon atom) meth-
(2 carbon atoms ) eth -
( 3 carbon atoms ) prop-
( 4 carbon atoms ) but -
( 5 carbon atoms ) pent -
( 6 carbon atoms ) hex -
( 7 carbon atoms ) hept-
( 8 carbon atoms ) oct -
( 9 carbon atoms ) non-
(10 carbon atoms ) dec-

Properties of Alkane:

1) Burns in plentify supply of air, it produces carbon dioxide and water.If INCOMPLETE COMBUSTION, it gives soot, carbon monoxide,carbon dioxide and water.

2) One reaction:Free radical Substitution
Alkane will react with Chlorine in UV light conditions ( means sunlight ) to form a variety of products:

Eg:
CH4 + Cl2 ---> CH3Cl + HCl ------ equation (1)

CH3Cl + Cl2 ---> CH2Cl2 + HCl ------ equation (2)

CH2Cl2 + Cl2 ---> CHCl3 + HCl ------- equation (3)

CHCl3 + Cl2 ---> CCl4 + HCl ----- equation (4)

Lastly, in exam, you are EXPECTED to name, form equations and draw the structure!

ALKENES

Formula of alkene :

CnH2n

Nomenclature

all alkanes begin with the prefix as mentioned below and ending with -ene

there is no methene ( 1 carbon )

(2 carbon atoms ) eth-

( 3 carbon atoms ) prop-

( 4 carbon atoms ) but-

( 5 carbon atoms ) pent-

( 6 carbon atoms ) hex-

( 7 carbon atoms ) hept-

( 8 carbon atoms ) oct-

( 9 carbon atoms ) non-

(10 carbon atoms ) dec-

Properties of alkene

1) Combustion

Burns in plentify supply of air, it produces carbon dioxide and water.

If INCOMPLETE COMBUSTION, it gives soot, carbon monoxide, carbon dioxide and water.

2) Hydrogenation

C2H4 + H2 ---> C2H6 (ethane)

3) Bromination

C2H4 + Br2 ---> C2H4Br2

** This is bromine test: used to distinguish between alkane and alkene ** ( Typical Structure Question!)

Alkene: Aqueous bromine will decolourised.
Alkane: Aqueous bromine remains unchanged.

4) Hydration

C2H4 + H2O ---> C2H5OH (ethanol)

Another method to prepare ethanol is 'fermentation'

C6H12O6 ---> 2 C2H5OH + 2 CO2

Conditions: yeast and temperature: 25'C.

5) Cracking

To break less useful linger chains into smaller useful fractions.

Conditions: 400°C - 700°C , silicon dioxide /aluminum oxide as catalyst.

OXIDATION & REDUCTION

There are basically 4 definitions of oxidation and reduction:

OXIDATION

1) Increase in oxidation states

Eg: Fe 2+ ---> Fe 3+

An increase of oxidation staes from 2+ to 3+ ( obvious, isn't it? )

2) Gain of oxygen atoms

Eg: Pb + CuO --> PbO + Cu

In this case, Lead (Pb) has gain 1 oxygen atom to form lead(II) oxide (PbO)

3) Lost of hydrogen atoms

Eg: 2 H2S (g) + SO2(g) ---> 2H2O(l) + 3S (s)

In this case, hydrogen sulphide (H2S) has lost 2 hydrogen atoms to form sulphur (S)

Note: do not be CONFUSED by the ratio: 2H2S.
We are interested in the formula, H2S instead!

4) Loss of electrons

Actually, if you look closely, the LOST of electrons is similar to the oxidation states!!!

Why Do I Say That?

Consider this example,
Fe 2+ ---> Fe 3+2+ means lost of 2 electrons and 3+ means lost of 3 electrons.In this case, we say that Fe 2+ is oxidised to Fe 3+.
Compare the oxidation states, isn't 2+ a gain of OXIDATION STATES to 3+ ??

Similarly,

REDUCTION

1) Decrease in oxidation states

Eg: Zn 2+ ---> Zn

From oxidation states of 2+ to 0 ( a decrease in oxidation states )

2) Loss of oxygen atoms

Eg: Pb + CuO ---> PbO + Cu

Copper (II) oxide has lost 1 oxygen atom to form Cu

3) Gain in hydrogen atoms

Eg: N2 + 3H2 ---> 2 NH3

Nitrogen (N2) has gain 2 hydrogen atoms to form ammonia (NH3)

4) Gain of electrons

Eg: Zn 2+ + 2 e- ---> Zn

Zinc ion has accepted 2 electrons to become Zinc ztom
or
Zinc ion has decrease in its oxidation state from 2+ to zero.

( the first rule about decrease in oxidation states )

SPEED OF REACTIONS

** IF THE QUESTION STATES THE USE OF COLLISION THEORY TO EXPLAIN THE FACTORS AFFECTING THE SPEED OF REACTION, PLEASE EXPLAIN USING THE PARTICLES!!!**

(Typical Structure Question!)

Factors affecting rate of reaction:

1) CONCENTRATION

* EXPLANATION *
The greater the number of particles, the more frequent is the collision,-----> the faster the speed of reaction.

2) EFFECTIVE SURFACE AREAS OF REACTANTS

* EXPLANATION *
The greater the effective surface area of reactants,the more frequent is the collision-----> the faster the speed of reaction.

3) TEMPERATURE

* EXPLANATION *
The higher the temperature, the greater the amount of energy the paricles have, the frequent is the collision,-----> the faster the speed of reaction.

4) CATALYST

* EXPLANATION *
The use of catalyst increases the speed of reaction.

Note: Catalyst is never used up in a reaction!!!

AIR

Composition of air

nitrogen- 78%

oxygen - 21%

other gases- 1% ---> carbon dioxide-0.03%---> noble gases - mainly argon.

NOTE: AIR DOES NOT CONTAIN HYDROGEN!!!!!!!

POLLUTANTS

For pollutants, pupils are expected to be able to least 2 pollutants: its sources, effects and solutions. (Questions on air have become very popular in examinations)

CARBON MONOXIDE

Source: incomplete combustion of fuels in vehicle engines
Solution:
1) ensure complete combustion of fuels
2) attach catalytic converter to vehicle engines.

OXIDES OF NITROGEN

Source:
1) combustion of fuel in vehicle engines at high temperature
2) lighting
Solution:
Fit catalytic converter to vehicle engines.

ACID RAIN

1) when sulphur dioxide dissolves in rain, sulphuric acid is formed.

2) when oxides of nitrogen dissolves in rain, nitric acid is formed.
(1) + (2) --- > ACID RAIN

Effects Of Acid Rain:

(1) Corrode buildings,
(2) corrode limestone structures,
(3) damage to trees and
(4) marine lives.

EXTRACTION OF METALS

Extraction of Iron

TYPICAL STRUCTURED/ ESSAY QUESTIONS

Question: Describe with the aid of equations the essential reactions in the extraction of iron.

1) Iron ore (haematite), coke and limestone are added to a blastfurnace.

2) Coke reacts with the air to form carbon dioxide.

3) Coke reacts with more carbon dioxide to form carbon monoxide.

4) Carbon monoxide reacts with iron ore to form iron and carbon dioxide gas.

5) Limestone decomposes to form calcium oxide and carbon dioxide.

6) Calcium oxide reacts with silicn dioxide to form slag.

Typical questions associating with extraction of iron:

(a) Name of the iron ore = haematite

(b) Why is limestone used in the extraction = to remove impurities ( acidic oxide, silicon dioxide )

_______________________________________________

Note:the extraction of metal depends on the reactivity of the metal.

Electrolysis of molten chlorides

Potassium, Sodium, Calcium, Magnesium, Aluminum

Heating with carbon

Zinc, Iron, Lead, Coppper

Uncombined in the ground

Silver, Gold, Platinum

ENERGY FROM CHEMICALS

EXOTHERMIC ( EXit )

Heat energy is released.

Egs: acid and metal reactions, neutralization, condensation, freezing and bond-making

Heat of Reaction (Enthalpy change) = negative

Tips for remembering: When two persons get together ( bond-making), they are in love and they will release 'sparks' of love ( 'Heat energy release') [ laugh]

ENDOTHERMIC

Heat energy is absorbed.

Eg: decomposition, melting, boiling, bond-breaking

Heat of Reaction ( Enthalpy change ) = positive

Tips for remembering: When a couple wants to break up ( bond-breaking), they need to gather all their complains and greviances to quarrel ('Heat energy gain') [laugh]

GROUP PROPERTIES

Typical Exam Questions!!!!(STR/ESSAY)

Group I ( alkali metals)

It is known as alkali metals because it reacts with water to form HYDROXIDES and hydrogen gas.

They are soft, low densities ( hence can be cut by knife ), having charges (+1) and the melting point decreases down the group. They are very reactive hence they need to be stored under oil to prevent reaction with air and water.

An Easy Way For Pupils To Remember the reactivity.......

'F' is the MOST REACTIVE !!!!!

For group I, Francium is the most reactive!!!! ( hence reactivity increases down the group )

Pupils are required to state the way the element react with water!!!!

Lithium reacts fast.
Sodium reacts quickly, catches fire sometimes explodes
Potassium reacts EXTREMELY FAST; catches fire and then EXPLODES.

As for rubidium, caesium and francium.... the reactivity will be explosion because they are more reactive than potassium.

Group VII ( halogen)

Each molecule is diatomic (F2, Cl2, Br2, I2, At2), having charges of (-1) and the boiling points increases down the group. They are very reactive and react VIGOROUSLY with metals to form ionic salts. Reactivity decreases down the group.

Remember: F is the most reactive.

Hence Fluorine is the most reactive, followered by chlorine, bromine, iodine and the least reactive is astatine.

As for the colours, it darkens down the group.

Fluorine is light yellow
Chlorine is yellow green
Bromine is brown
Iodine is dark purple ( black is acceptable)
Astatine is black

Since the boiling points increases down the group, the states are as follows:

Fluorine-(gas)
Chlorine-(gas)
Bromine-(liquid)
Iodine-(solid)
Astatine-(solid)

Since reactivity decreases down group 7, A MORE REATIVITY HALOGEN WILL BE ABLE TO DISPLACE A LESS REACTIVE HALOGEN FROM AN AQUEOUS SOLUTIONS OF ITS SALT.

This means that fluorine is able to displace (kick out) all the rest of the elements from group 7:

F2 (g) + 2 NaCl(aq) ----> 2 NaF(aq) + Cl2(aq)

However, a less reactive halogen will not be able to displace a more reactive halogen:

Cl2(g) + NaF (aq) ---> no reaction

GROUP 8 ( NOBLE GASES )

These elements are not able to combine with other atoms because of its stable electronic configuration ( octet structure can be used to replace 'stable-electronic configuration').
Hence group 8 elements are MONOATOMIC.

Pupils will need to know the uses:

Helium-hot air balloon
Neon- advertising lights
Argon / Neon - in light bulbs
Argon - manufacturing of steel ( flush air from molten steel to protect it from further reaction of the air )