GCE O Level Chemistry SPA

MSN :D

2009-05-28T07:26:00.001-07:00

GONG XI FA CAI

2009-01-23T07:58:00.000-08:00

Chemistry Electrolysis Mindmaps

2009-01-23T07:39:00.000-08:00

Chemistry SPA Skill 3 Effect of conc. on speed of reaction

2009-01-21T21:25:00.000-08:00

Chemistry SPA FUELS AND OIL

2009-01-20T18:34:00.001-08:00

Chemsitry SPA Skill3 Deetermine most conc. or least conc. acids

2009-01-20T06:44:00.001-08:00

CHEM SPA SKILL 3 CATALYTIC DECOMPOSITION of HYDROGEN PEROXIDE

2009-01-20T06:34:00.000-08:00

CHEM SPA SKILL 1 and 2 CONC. OF SULPHURIC ACID PRACT TITRATION

2009-01-20T06:32:00.001-08:00

CHEM SPA SKILL 1 and 2 CONC. OF SULPHURIC ACID PRACT TITRATION

Chemistry SPA SKILL 3 Speed of Reaction between magnesium and HCl

2009-01-20T06:29:00.000-08:00

Chemistry SPA SKILL 3 Speed of Reaction between magnesium and HCl

Chemistry SPA Titration1 PRACT NOTES

2009-01-20T06:23:00.000-08:00

CHEMISTRY SPA SKILL 1 AND 2

TITRATION PRACTICE 1

PROPER FORMAT TO ACE CHEM SPA TITRATION SKILL 1 AND 2

Titration SPA answers

Titration no.	1	2	3	4
Final reading/cm3	21.4	20.9	20.6	20.4
Intial reading/cm3	0.0	0.0	0.0	0.0
Volume of P used/cm3	20.4	20.9	20.6	20.4
Best titration results

Average volume of P used= 20.9 +20.6+ 20.4

=20.6 cm3

Volume of Q used= 25.0 cm3

To find no. of moles of Sodium Tetraborate in 1 dm3 of Q Concentration(mol/dm3)

No. of moles of Sodium Tetraborate

---------------------------------------------------- = 1/2

No. of moles of HCl

------------------------------------------

No. of mols of HCl= Conc X vol (mol/dm3) = 0.100 mol/dm3 X 0.0204 dm3
=0.00102

Conc. Of Sodium Tetraborate= No.of mols/vol.
= 0.00102 mol/0.025dm3
=0.0408mol/dm3

Conc. Of Sodium tetraborate = 18.5 g/dm3

0.0408 mols =rep 18.5 g

1 mol rep 18.5/0.0408 = 453.43

Molar Mass= 453.43 g

Conc. In g/dm3 = conc in mol/dm3 X molar mass

18.5 = 0.0408 X molar mass

Molar mass = 18.5/0.0408=453.43

Mr of Na2B4O7xH20 = 23 x 2 +11 X 4 +16X 7 +18X

= 202+18x

202+18x rep 453.43

X= 13.968

= 14.0

One key source of experiment error:

The detergent (Solution Q)might contain other impurities, such as other alkalis, hence excessive HCl might be needed.

CHEM SPA WORKSHEET 2

2009-01-19T06:21:00.000-08:00

CHEM SPA WORKSHEET 2

CHEMISTRY SPA SKILL 3 TECHNIQUE

2009-01-19T06:14:00.000-08:00

CHEMISTRY SPA SKILL 3 TECHNIQUE

Chem SPA1 Worksheet

2009-01-19T06:13:00.001-08:00

Chem SPA1 Worksheet

Chemistry SPA

2009-01-18T14:58:00.000-08:00

Chemistry SPA

Practice

Chapter 20 The atmosphere and the Environment

2008-12-26T23:13:00.000-08:00

Chapter 20 notes

The atmosphere and the Environment

DOWNLOAD:

http://www.mediafire.com/?2ixtz0izbjj

GCE ‘O’ Level Pure Chemistry (5070) November 1999

2008-12-26T23:12:00.000-08:00

GCE ‘O’ Level Pure Chemistry (5070) November 1999

Paper 1 (5070/01)

1	2	3	4	5	6	7	8	9	10
A	B	C	B	B	B	A	D	D	D

11	12	13	14	15	16	17	18	19	20
C	A	C	D	A	D	A	C	D	D

21	22	23	24	25	26	27	28	29	30
C	C	B	D	A	C	B	D	C	B

31	32	33	34	35	36	37	38	39	40
C	B	D	A	B	B	A	A	C	A

Question	Explanations
4	Question involving ink does not necessary have to be related to chromatography. The question wants the separation of pure water from ink and thus, the answer would be distillation.
6	The atom and ion of sodium do not contain the same number of electrons. Thus, we would need to look at the number of neutrons which is not affected by the gain or loss of electrons.
9	Read the question carefully. This question is asking for the total number of electrons in the covalent bonds surrounding the S atom. There are six covalent bonds (double bond = two covalent bonds) surrounding the S atom and so there are (6x2=12) electrons.
12	The electrodes have been changed to copper and so, instead of discharging OH^- ions at the anode, the copper metal of the anode is oxidized.
15	The question concerned the rates of reaction only and not how pressure affects rates and position of equilibrium. Therefore, increasing the pressure of the system would increase the speed of both forward and backward reaction.
33	Calcium sulphate was the only compound which was not a base and therefore did not change the pH of an acidic soil.
38	Addition reactions usually produce one product and option A was the only reaction that has more than one product.

Paper 2 (5070/02)

Section A and B

Answers

(a) potassium

(b) lead (II) bromide/ zinc oxide

(d) lead (II) bromide

(e) carbon

(f) oxygen

(g) hydrogen

(a) 80^oC

(b) It remains constant until all the substance has melted.

(c) It is because the melting point of the substance is 80^oC and boiling point is 215^oC. [1] The melting point of water is 0^oC and the boiling point of water is 100^oC. [1]

{Common mistake: never compare the melting or boiling point of water and the substance. Need to discuss both water and substance to earn the full marks}

(ai) It refers to a reversible reaction.

(aii) {not in syllabus} Removal of carbon dioxide causes the equilibrium to shift to the right thereby producing more calcium oxide.

(bi) CaO (s) + H₂O (l) ® Ca(OH)₂ {slaked lime is calcium hydroxide}

(bii) It is used to neutralize acidity in soil.

{Rejected answers: testing for carbon dioxide, making chalk, making paint, as a fertilizer and in the blast furnace}

(ai) Brown gas (bromine gas) moves up the other gas jar. After some time, both layers have a uniform brown colour.

{Note: bromine gas is brown and not red. Must mention the colour of bromine to earn the mark}

(aii) Diffusion has taken place. The bromine molecules move from a region of higher concentration to a region of lower concentration.

(bi) The rate of change would be faster.

(bii) This is because the molecular mass of nitrogen dioxide is smaller than bromine. Therefore, nitrogen dioxide diffuses at a faster rate.

(a) It is a process in which oxygen is added to the substance. OR A reaction in which there is an increase in oxidation state.

(bi) Name: Propanol Structure: H H H

| | |

H-C-C-C-O-H

| | |

H H H

(bii) It is higher than the boiling point of ethanol. This is because as the molecules become bigger, the intermolecular forces are stronger. More energy is required to overcome the forces. Therefore, propanol would have a higher boiling point.

(ci) ethyl ethanoate

(cii) CH₃COOH + C₂H₅OH D CH₃COOC₂H₅ + H₂O

{Common mistake: missed out water from the equation}

(a) gaseous state

(b)

{Common mistake: inner electrons drawn instead of showing only outer electrons}

(ci) H⁺

(cii) The solution turns reddish brown.

{Common mistake: the brown solution was decolourised}

(ciii) Cl₂ + 2Br^- ® 2Cl^- + Br₂

(a) nitrogen is needed for the formation of protein for healthy plant growth.

(b) The ammonium and nitrate ions will break free from each other in the lattice arrangement and move about freely and occupy spaces between the water molecules.

{Common mistake: never explain in terms of particles}

% of nitrogen in NH₄NO₃ = (28/80) x 100% = 35%

% of nitrogen in urea = 47% (given)

Therefore, 1 kg of urea contains more nitrogen than 1 kg of ammonium nitrate.

{Common mistake: never compare the % of nitrogen of both compounds}

(ai) Limestone {Common mistake: haematite (iron ore is given in the question!)}

(aii) To produce calcium oxide which is then used to remove acidic impurities

{Note: need to mention the name of the impurities (sand or silicon dioxide) removed or state acidic impurities to earn the mark. Common mistake: vague answers such as ‘to remove impurities’ or ‘to produce slag’}

(bi) carbon monoxide

(bii) CO₂ + C ® 2CO

{Common mistake: never mention ‘mixture’ in the answer}

(d) mild steel: it will rust; aluminium: it is very light

{Common mistake: cars blowing away because aluminium was so light!}

Section B

(ai) catalytic cracking

(aii) It acts as catalyst.

{common mistakes: for decomposition/ to distribute heat/ to make a bigger surface are}

(bi) C₃H₈ ® C₂H₄ + CH₄; Bubble the gas into aqueous bromine. The aqueous bromine will decolourise.

{Common mistake: just mention ‘bromine’ and not ‘aqueous bromine/ bromine water’}

(bii) 1 volume of C₃H₈ produces 1 volume of C₂H₄.

100 cm³ of C₃H₈ produce 100cm³ of C₂H₄.

{Common mistake: using M_r values of propane and ethene to give 100 x 28/44= 66cm³}

(ci) Polypropene

(cii) Addition polymerization

H H H H H H H H

| | | | | | | |

… + C=C + C=C + … ® …-C-C ¾ C-C-…

| | | | | | | |

H CH₃H CH₃ H CH₃H CH₃

{Common mistake: drawing poly(ethene) instead of poly(propene)}

(ciii) They cannot be decomposed by bacteria in the soil.

{Common mistake: Never mention ‘bacteria’ in the answer which is the ‘bio’ part of the term ‘biodegradable’}

B10

(ai) C₄H₁₀ + 13/2 O₂ ® 4CO₂ + 5H₂O

(aii) no. of moles of butane = volume/molar volume = 16/24 = 2/3

1 mole of butane gives off 2880kJ of heat.

2/3 mole of butane gives (2/3 x 2880) = 1920 kJ of heat

(aiii) The value of ∆H is negative showing that the reactants have more energy than the products.

(bi) {not in syllabus} Silver metal is formed.

(bii) The silver ion is reduced to silver. Ag⁺ + e ® Ag

(biii) used to coat photographic film

{note: must mention the term ‘film’ to earn the mark}

B11

(a) Cryolite acts as a solvent to dissolve the aluminium oxide. It lowers the melting point of aluminium oxide so that less energy is needed. It melts the aluminium oxide and maintains the electrolyte in a molten state.

(b) Cathode: Al³⁺(l) + 3e ® Al (l)

Anode: 2O^2-(l) – 4e ® 2O₂ (g)

(di)

The impure copper is used as the anode and pure copper, the cathode.

{Note: must mention the electrolyte as aqueous copper (II) sulphate and not just copper (II) sulphate.}

(dii) At the anode: The anode dissolves in solution. Cu ® Cu²⁺+ 2e The copper (II) ions move to the cathode.

At the cathode. The Cu²⁺ ions are discharged and pure copper is formed on the cathode. Cu²⁺+ 2e ® Cu

B12

(a) fractional distillation; difference in boiling point

{Common mistake: never mention ‘difference’ in the boiling points of the gases}

(bi) vanadium (V) oxide

{Common mistake: omission of oxidation state of vanadium}

(bii) 2 SO₂ + O₂ ® 2 SO₃

no. of moles of SO₂= 3200/64 = 50

no. of moles of SO₃= 50

mass of SO₃ = 50 x (32+16x3)g

= 4000g = 4kg

(biii) Sulphur trioxide is dissolved in concentrated sulphuric acid to form oleum.

H₂SO₄ + H₂O ® H₂S₂O₇

Oleum is then converted to sulphuric acid by adding water to it.

H₂S₂O₇+ H₂O ® 2H₂SO₄

{Common mistake: omission of ‘concentrated’ for the sulphuric acid in the first step}

(ci) Sulphur dioxide dissolves in water to form acid rain. Acid rain will corrode limestone buildings and kill fishes in lakes. Sulphur dioxide will also cause breathing difficulties.

(cii) Neutralisation reaction {Note: SO₂ is an acidic oxide}

GCE O Level Pure Chem Answers 1998 TYS

2008-12-26T23:11:00.000-08:00

GCE ‘O’ Level Pure Chemistry (5070) November 1998

Paper 1 (5070/01)

1	2	3	4	5	6	7	8	9	10
B	D	D	A	A	B	D	D	A	C

11	12	13	14	15	16	17	18	19	20
B	C	D	D	C	B	C	B	C	D

21	22	23	24	25	26	27	28	29	30
C	B	B	B	A	C	B	B	B	D

31	32	33	34	35	36	37	38	39	40
A	D	C	B	B	C	B	C	C	B

Question	Explanations
6	Xenon is incorrect as it does not have the same number of electrons as Krypton. However, it has the same number of outer electrons. The answer is Rubidium (Group I) as it has 37 electrons and loses 1 electron to form Rb⁺ which gives 36 electrons.
14	A solution of an ionic compound contains H⁺ and OH^- from water as well as the constituent ions of the compound.
19	Potassium manganate (VII) is the only oxidizing agent present in the options which can oxidize iron (II) ions to iron (III) ions.
21	Calcium carbonate when added in excess would neutralize nitric acid without leaving an alkaline solution.
34	Graphite, consists of only one type of atom i.e. carbon atoms and therefore is an element and not a compound.

Paper 2 (5070/02)

Section A and B

Answers

(a) Cl

(b) I, Cl, H, O, N, Br (any one of these)

(d) Na, K (any of the Group I metal)

(e) O

(f) Fe

{note: no marks will be awarded for writing answer in words instead of symbols}

(ai) tungsten and aluminium

(aii) they conduct electricity when solid and have high melting point

(b) Wax melts over a range of temperature (35-50^oC)

{common mistake: mixture has a low melting point}

(ci) sodium chloride

(cii)A substance containing 2 or more elements joined together by a chemical reaction.

(d) At 659^oC, aluminium is a solid. The particles are closely packed in an orderly arrangement. The particles can only vibrate about their fixed position. At 661^oC, aluminium became a liquid. The particles are now in a disorderly arrangement and they can move throughout the liquid.

(e) Add water to the mixture. Sodium chloride dissolves but not sulphur. Filter the mixture. The residue is sulphur and the filtrate is sodium chloride solution. Heat the sodium chloride solution in an evaporating dish until all the water has evaporated. Sodium chloride is left in the dish.

(a) A substance containing carbon and hydrogen only.

{common mistake: omitting the word ‘only’}

(b) Fraction D

(ci) X is C₄H₈

(cii) H H H H H H H H

| | | | | | | |

H-C-C-C=C-H H-C-C=C-C-H

| | | |

H H H H

(ciii) The hydrocarbon X can be polymerized because it contains a carbon-carbon double bond.

(a) 2H₂ + O₂ ® 2H₂O

(b) Redox reaction is a reaction in which oxidation and reduction occurs at the same time. In this reaction, one substance gains oxygen while the other substance loses it oxygen.

{must mention the second sentence to earn the full marks}

(d) Burning of hydrocarbon is likely to lead to the formation of carbon monoxide which is a pollutant. Burning of hydrogen will only form water which is not a pollutant.

(e) No. of moles of hydrogen gas = 50/2 = 25 moles

Volume of hydrogen gas = 25 x 24 = 600 dm³

{Note: hydrogen gas in H₂ not H}

(ai) Beaker B

(aii) 2 AgNO₃ + Cu ® Ag + Cu(NO₃)₂

{Common mistake: writing CuNO₃}

(b) Beaker A and D {because Zn is more reactive than Ag and Cu. A more reactive metal will displace a less reactive metal from its salts}

(c) Aluminium has a layer of oxide coated on it. The oxide layer protects the aluminium from reacting with other substances.

(a)

particle	charge	mass
Proton	+1	1
Neutron	0	1
Electron	-1	1/2000

{Common mistake: never include ‘+’ sign for the charge of proton}

(b) Because they have the same number of protons but different number of neutrons

Explanation: 1 Tritium atom has 1 proton, 1 electron and 2 neutrons. Hence, the relative atomic mass of 1 Tritium atom is 3 and the relative molecular mass of a Tritium molecule, T₂ is 6.

{Common mistake: giving relative atomic mass (which is 3) as the answer}

(di) CaH₂

(dii)

{Note: Hydride ion is H^-. Therefore, hydride ion is formed when hydrogen takes in 1 more electron}

(a) 1. The impure copper should be connected to the positive terminal of the battery and the pure copper – the negative terminal.

2. The electrolyte used should be copper (II) sulphate solution and not NiSO₄.

(b) Cu(s) – 2e ® Cu²⁺ (aq)

{Common mistake: failure to include state symbols in equation}

Section B

(a) Na⁺ and PO₄^3-

(bi) sodium hydroxide

(bii) H₃PO₄ + 3 NaOH ® Na₃PO₄ + 3H₂O

(c) Titration method is used. Fill a burette with phosphoric acid. Pipette 25cm³ of sodium hydroxide into a conical flask. Add in 2 drops of the given indicator. Add in phosphoric acid from the burette until the conical flask shows a colour change. Note the volume of phosphoric acid used. Repeat the experiment using 25cm³ of sodium hydroxide and the same volume of phosphoric acid with no indicator added. The solution obtained is pure sodium phosphate. Pour some of the solution into an evaporating dish. Warm the solution until it is concentrated. Allow the concentrated solution to cool. Crystals of sodium phosphate is formed. Filter to remove the crystals and dry between sheets of filter papers.

{Common mistake: (1) fail to mention the need to repeat the titration WITHOUT an indicator (2) mention ‘evaporation to dryness’ or vague answers such as ‘heating the solution’ without making a clear point whether it was to dryness or saturation}

(di) Carbon dioxide

(dii) Bubble the gas into limewater. A white precipitate is formed.

(ei) Ca₃(PO₄)₂

(eii) Calcium phosphate provides the plant with phosphorus.

(ai) Ethanoic acid H O

| ||

H-C-C-O-H

{Common mistake: missing bond between O and H}

(aii) The acid is formed when ethanol is oxidized by bacteria from air or by adding acidified potassium dichromate (VI) which is an oxidizing agent.

(bi) Phosphoric acid as catalyst, temperature of 300^oC and 65 atmospheric pressure

(bii) Given 72 dm³ of ethene

No. of moles of ethanol/no. of moles of ethene = 1/1

No. of moles of ethene = volume/molar volume = 72/24 = 3 moles

No. of moles of ethanol = 3 moles

Mass of ethanol = 3 x molar mass = 3 x (12x2+1x5+16+1) = 138g

(d) Ethanol is used as a solvent in perfumes and paints, as a fuel for motor vehicles, in the manufacture of ethanoic acid.

{Common mistake: vague answers such as ‘solvent’ (neglecting ‘in product’ such as perfumes) and ‘fuel’ (neglecting ‘for motor vehicles’) were insufficient to score}

B10

(ai) Lithium floats on water and dissolves rapidly. Effervescence is seen.

{Note: question is looking for observations and not inferences}

(aii) Add a piece of red litmus paper. The paper will turn blue.

(bi) The rate of reaction decreases (or the reaction slows down with time)

{Common mistake: rate becomes ‘constant’}

(bii) Because lithium is used up completely

(di) 340 cm³

(dii) Volume of H₂ produced in experiment 2 = 170 cm³

Volume of H₂produced in experiment 3 = 340 cm³

(diii) Rate of reaction for experiment 2 is slower than experiment 1. This is because 0.1g of lithium has a smaller surface area than 0.2g of lithium. Rate of reaction for experiment 3 is faster than experiment 1. This is because of higher temperature.

B11

(a) Place a moist blue litmus paper into the gas jar. The gas will turn the blue litmus paper red and then bleached.

(b) A white solid is formed. (because NaCl is formed and NaCl is a white solid)

{Note: question is looking for observations and not inferences}

{Note: Chlorine is Cl₂ not Cl!}

(d)

(ei) Sodium chloride is an ionic compound. The ionic bonds holding the ions are very strong. Lots of energy is needed to break the bonds. Therefore, sodium chloride has a high melting point.

(eii) When molten, the sodium ions and chloride ions can move about freely to carry current.

{Common mistake: moving ‘electrons’ instead of ‘ions’}

Chemistry TYS answers 1997 papers

2008-12-26T23:07:00.000-08:00

GCE ‘O’ Level Pure Chemistry (5070) November 1997

Paper 1 (5070/01)

1	2	3	4	5	6	7	8	9	10
B	D	B	A	D	C	C	A	D	B

11	12	13	14	15	16	17	18	19	20
B	B	C	C	D	D	C	A	C	A

21	22	23	24	25	26	27	28	29	30
C	C	A	C	B	B	C	A	A	D

31	32	33	34	35	36	37	38	39	40
D	A	D	A	D	A	A	A	B	C

Paper 2 (5070/02)

Section A and B

Qn	Answers
A1	(a) air {common mistakes: glass and limestone} (b) glass {not in syllabus} (c) brass {common mistake: air} (d) water/ salt (e) sugar/ limestone
A2	(a) krypton (b) 10 (c) Molar mass of Ar = 40g Molar volume of Ar at r.t.p. = 24 dm3 Density of Ar = 40/24 = .1.67g/dm3 (d) 215K {if unit given is in ^oC – no mark} (e) fractional distillation of liquid air (f) Argon is present in a larger quantity than other gases.
A3	(ai) H H H H H H H H \| \| \| \| \| \| \| \| H-C-C=C-C-H H-C-C-C=C-H \| \| \| \| H H H H {common mistake: but-1-ene} (aii) C₄H₈ + Br₂ ® C₄H₈Br₂ (aiii) alkene: colourless; bromine: reddish-brown; reaction product: colourless (aiv) Alkene is unsaturated and a single product is formed. (bi) C₉H₁₂ (bii) boiling point/ density/ viscosity {note: an increment of CH₂ in the molecular formula is not allowed as a physical property}
A4	(a) P: anhydrous copper (II) sulphate; Q: water {common mistake: never mention oxidation state for Cu} (bi) barium sulphate (bii) H⁺ and SO₄^2- {CuSO₄ ® CuO + SO₃, SO₃ + H₂O ® H₂SO₄} (biii) copper (II) oxide {common mistake: never mention oxidation state for Cu}
A5	(ai) hydrogen; because it is lighter (aii) molecules move faster (bi) 2H₂ + O₂ ® 2 H₂O (bii) water and oxygen {note: oxygen is in excess because 2 vol. of H₂ react with 1 vol. of O₂} (c) formation: In the car engine, the temperature is very high. The oxygen and nitrogen in the surrounding air react to form oxides of nitrogen. limiting its formation: The emission can be limited by installing a catalytic converter so that the oxides of nitrogen can be converted to harmless gases. (d) sulphur dioxide
A6	(a) dilute sulphuric acid (b) Overall reaction: Zn + 2H⁺ ® Zn²⁺ + H₂ {Zn – 2e ® Zn²⁺, 2H⁺ + 2e ® H₂} {common mistake: misread the question and gave half equations for the reactions at the electrodes} (c) A more reactive metal gives a higher meter reading. (d) 2.72 – Magnesium, 2.00 – Aluminium, 1.10 – Zinc, 0.78 – Iron, 0.00 - Copper
	Section B
B7	(ai) At the anode, for every 1 mole of O₂ formed, 4 moles of electrons is given out by OH^-. At the cathode, for every 1 mole of H₂ formed, only 2 moles of electron is taken in by H⁺. Hence, volume of O₂ formed is only half that of H₂/ volume of H₂ twice that of O₂. {Common mistake: using the formula of water to answer the question} (aii) SO₄^2- (b) At the anode, the product formed is oxygen gas and product formed at the cathode is hydrogen gas. (ci) Aluminium is manufactured by the electrolysis of molten aluminium oxide, using carbon as the electrode. The molten aluminium oxide is dissolved in molten cryolite to lower its melting point. During electrolysis, the following reaction occurs. At the anode: 2O^2- - 4e ® O₂ At the cathode: Al³⁺ + 3e ® Al Aluminium is formed at the cathode. During electrolysis, the carbon anode must be changed periodically as oxygen given out will react with the carbon anode to form carbon dioxide gas. (cii) making drink cans/ aluminium foil for wrapping food {Note: vague answers such as using aluminium to make windows or kitchens are not allowed} (d) Amphoteric oxide is a metal oxide that reacts with both acid and alkali to form salt and water.
B8	(ai) burette and pipette (aii) methyl orange; from yellow to orange (aiii) aq: aqueous, l: liquid (bi) no. of moles of NaOH/ no. of moles of HCl = 1/1 no. of moles of NaOH = 0.025 x 1 = 0.025 moles no. of moles of HCl = 0.025 moles volume of HCl = no. of moles/concentration = 0.025/2 = 0.0125 dm³ (bii) no. of moles of NaCl/ no. of moles of NaOH = 1/1 no. of moles of NaCl = 0.025 moles mass of NaCl = 0.025 x 58.5 = 1.46g (ci) E is a metal because it gives away 2 electrons to form E²⁺O^2- (cii) Group II because it gives away 2 electrons.
B9	(ai) To prevent steel alloy from rusting (aii) SnCl₄ (aiii) Covalent because SnCl₄ has a low boiling point. (aiv) SnCl₄ ® Sn + 2Cl₂ The oxidation state of Sn decreases from +4 (in SnCl₄) to 0 (in Sn) showing reduction. The oxidation state of Cl increases from -1 (in SnCl₄) to 0 (in Cl₂) showing oxidation. Since oxidation and reduction occur at the same time, this is a redox reaction. {note: must mention both reduction of tin and oxidation of chlorine to earn the marks} (bi) {not in syllabus} Diamond and Graphite (bii) {not in syllabus} Diamond is used in saws and drills to cut hard solids. This is because diamond is very hard. It has a macromolecular structure. Each carbon atom is bonded to four other atoms tetrahedrally by strong covalent bond. Graphite is used as a lubricant. The carbon atoms are arranged in layers. These layers of atoms can slide over each other easily because of weak intermolecular forces and thus, graphite is greasy and soft. Or graphite can be used as electrodes because it contains electrons which are free to move to carry current.
B10	(ai) Fine powder has a larger surface area. Reaction will be faster. (aii) by measuring the decrease in volume of hydrogen with time {common mistakes: (1) mentioning hydrogen being evolved instead of decreasing (2) ignoring the time factor} (aiii) because it is a transition metal (b) since one molecule of oil has only 1 double bond, one mole of the oil will react with 1 mole of hydrogen no. of moles of oil/ no. of moles of H₂ = 1/1 no. of moles of H₂ = (60/1000)/24 = 0.0025 moles no. of moles of oil = 0.0025 moles molar mass of oil = mass/ no. of moles = 0.5/0.0025 = 200 therefore, relative atomic mass of oil = 200 {common mistake: fail to convert 24 dm³ to 24000 cm³ in calculations} (ci) Glycerol and soap (cii) Terylene {common mistake: giving ‘polyester’ as the answer}

1	2	3	4	5	6	7	8	9	10
A	B	C	B	B	B	A	D	D	D

11	12	13	14	15	16	17	18	19	20
C	A	C	D	A	D	A	C	D	D

21	22	23	24	25	26	27	28	29	30
C	C	B	D	A	C	B	D	C	B

31	32	33	34	35	36	37	38	39	40
C	B	D	A	B	B	A	A	C	A

1	2	3	4	5	6	7	8	9	10
B	D	D	A	A	B	D	D	A	C

11	12	13	14	15	16	17	18	19	20
B	C	D	D	C	B	C	B	C	D

21	22	23	24	25	26	27	28	29	30
C	B	B	B	A	C	B	B	B	D

31	32	33	34	35	36	37	38	39	40
A	D	C	B	B	C	B	C	C	B

1	2	3	4	5	6	7	8	9	10
B	D	B	A	D	C	C	A	D	B

11	12	13	14	15	16	17	18	19	20
B	B	C	C	D	D	C	A	C	A

21	22	23	24	25	26	27	28	29	30
C	C	A	C	B	B	C	A	A	D

31	32	33	34	35	36	37	38	39	40
D	A	D	A	D	A	A	A	B	C

1	2	3	4	5	6	7	8	9	10
A	B	C	B	B	B	A	D	D	D

11	12	13	14	15	16	17	18	19	20
C	A	C	D	A	D	A	C	D	D

21	22	23	24	25	26	27	28	29	30
C	C	B	D	A	C	B	D	C	B

31	32	33	34	35	36	37	38	39	40
C	B	D	A	B	B	A	A	C	A

1	2	3	4	5	6	7	8	9	10
B	D	D	A	A	B	D	D	A	C

11	12	13	14	15	16	17	18	19	20
B	C	D	D	C	B	C	B	C	D

21	22	23	24	25	26	27	28	29	30
C	B	B	B	A	C	B	B	B	D

31	32	33	34	35	36	37	38	39	40
A	D	C	B	B	C	B	C	C	B

1	2	3	4	5	6	7	8	9	10
B	D	B	A	D	C	C	A	D	B

11	12	13	14	15	16	17	18	19	20
B	B	C	C	D	D	C	A	C	A

21	22	23	24	25	26	27	28	29	30
C	C	A	C	B	B	C	A	A	D

31	32	33	34	35	36	37	38	39	40
D	A	D	A	D	A	A	A	B	C

1	2	3	4	5	6	7	8	9	10
A	B	C	B	B	B	A	D	D	D

11	12	13	14	15	16	17	18	19	20
C	A	C	D	A	D	A	C	D	D

21	22	23	24	25	26	27	28	29	30
C	C	B	D	A	C	B	D	C	B

31	32	33	34	35	36	37	38	39	40
C	B	D	A	B	B	A	A	C	A

1	2	3	4	5	6	7	8	9	10
B	D	D	A	A	B	D	D	A	C

11	12	13	14	15	16	17	18	19	20
B	C	D	D	C	B	C	B	C	D

21	22	23	24	25	26	27	28	29	30
C	B	B	B	A	C	B	B	B	D

31	32	33	34	35	36	37	38	39	40
A	D	C	B	B	C	B	C	C	B

1	2	3	4	5	6	7	8	9	10
B	D	B	A	D	C	C	A	D	B

11	12	13	14	15	16	17	18	19	20
B	B	C	C	D	D	C	A	C	A

21	22	23	24	25	26	27	28	29	30
C	C	A	C	B	B	C	A	A	D

31	32	33	34	35	36	37	38	39	40
D	A	D	A	D	A	A	A	B	C