Nyamira District Mocks 2006

233/1 CHEMISTRY PAPER 1

MARKING SCHEME

1. i) Luminous  1mk ii) Flame is sooty; less hot and takes long 1mk iii) Open air hole fully to allow adequate mixing of laboratory gas with air for complete combustion

2. Z is more reactive than y ½ it is easier to remove an electron from Z than from( 1mk) because less energy is required ½ mk 3. a) H H CH3    H – C – C - C – C  C– H 1mk    H H CH3

b) i) Propyl ethanoate  1mk ii) 3 – Bromo 2methy pent -1-ene 1mk 3- bromo 2- methyl pent – l – ene OR 3, 2 – bromomethylpent – l- ene 4.

Anode – ½ mk Cathode – ½ mk

i) U- oxygen  ½ mk V- hydrogen  ½ mk Anode rexn - ii) 4OH (aq) D2 (q)+ 2H2O(l) + 4e1

5. a) From the equation 54g of Al react with 7200cm3 3g ?  ½

3 x 72000  ½ = 4000 cm3 54 = 4 litres  ½ b) 54g produce 267g of AlCl3 3g ?  ½

3 x 267 = 14.83g ½ 54  ½ 6. i) X- hydrogen bond ½ mk W- covalent bond ½mk ii) Hydrogen bond exists in water molecule due to unequal sharing of electrons between O-H but methane has van der waals forces which are weaker  mk or WTTe 1 7. Copper metal :- increases  ½ because it absorbs / combines with oxygen to form copper ½ (II) oxide Sulphur powder :- Reduces ½ because it combines with oxygen to form sulphur (iv) oxide ½ which escapes ½ reducing mess

8. a) Ammonium chloride / NH4Cl(s)  1

b) Rate NH3 = 60  40 ½ Rate Hcl t t

3 = 60 x t = /2  ½ t 40 c) Graham law constant pressure and temperature the rate of diffusion of a gas is inversely proportional 9. a) sulphur (iv) oxide  1 b) Removes ammonia gas by reacting with it  1

10. Half- life is the time taken for a radio active isotope substance to decay into half its original mass 1mk

1 b) 1 ½ ¼ /8 t1 = 3 half – lifes  1 2 2 x 3 = 6 hours

11. C H O 26.7 2:2 71.1 RAM 12 1 16 No. of moles 26.7 = 2.23 2.2 = 2.2 71.1 = 4.44 12 1 16 All 3 correct ½ mk

Mole ratio 2.23 = 1 2.2 = 1 4.44 = 2 2.2 2.2 2 All 3 correct ½ mk

Mole ration 1: 1: 2

EF CHO2  ½ b) (CHO2)n = 90 45n = 90 n = 2 ½

MF = C2H2O4 ½

12. i) A hydrolysis mk ii) B Bromopropanolmk

iii) C Acidified KMnO4 or K2 Cr2 O7mk

13. a) - Purple colour is deposited at the bottom of the crucible due to iodine subliming - White solid of NaCl remains in the beaker b) To cool iodingevapour to iodine solid.

2 14. H H H H     H – C – C - H + Cl – Cl H - C – C - C– Cl + HCl  1mk     H H H H

Broken Formed

6(H- C) = 416 x 6 5(H- C) = 414 x 5 = 2070 = 2484 CL- Cl = 432 x 1 = 4320 H – Cl = 340 x 1 = 340 Cl- Cl = 243 x 1 = 243 C - C = 348 = 348 - 3190 C - C = 348 mk + 3075 mk

H = +3075 – 3190 = - 115 Kjmol -1mk

15. Q i) Potassium1/ sodium 1/ cal calcium1 / magnesium1

R – copper (ii) oxide / Cuo 1

ii) Redox (Reduction & oxidation)1

Because Cuo is reduced to copper metal while H2 is oxidized to H2O1

16. Mass of the solute = 142 – 23 = 119g ½

Mass of water 192 - 142 = 50 g ½

Solubility = 119 x 100 = 238g/ 100g of water1 501 + 17. a) i) NH 4  1 ii) OH-  1

b) H2S in a weak acid while H2SO4 is a strong acid

18. i) C ii) A 19. Protons : 301 Neutrons = 65 – 30 = 321

3 20. - Hot platinum wire continues to glow - Brown fames / gas given out in the flask 1 - Platinum is a catalyst for oxidation of ammonia1 the reaction is exothermic and takes place on its surface. Hence , the heat produced keeps the wire glowing 4NH3(g) + 5O2(g) NO(g) + 6H2O

NO is immediately oxidised by air to from nitrogen (iv) oxide, a brown gas 1

2NO(g) + O2(g) 2NO2 (g)

- -1 21. ClO 3 = x- 6 = x = +51

- ClO 4 = x – 8 x = +7 1

22. LJK2 or KJL  1

23. Zn(s) + 2HNO3(aq Zn (NO3)2(aq) + H2O(l) 1

Na2CO3(s) Na2CO3(aq) 1

Na2CO3(aq) + Zn(NO3)2(aq) Zn CO3(s) + 2NaNO3(aq) 1

2- 2+ CO (aq) + Zn (aq) ZnCO3(s) 1 Max 3 3 24. a) wet / moisture 1

b) Yellow solid1 colourless liquid1 formed in the lower jar Explanation Max 1

H2S is oxidized to sulphur (yellow solid )while SO2 is reduced1 to sulphur OR 1 reduced

2H2S(g) + SO2(g) 3S(s) + 2H2O

Oxidised  1 25. In the experiment magnesium reacts with both oxygen1 and nitrogen1 while zinc reacts with oxygen only1. 26. P1 = 760mmHg 3 V1 = 600cm

T1 = 273 + 25 = 298 K  ½

T2 = 273 + 50 = 323K  ½ P2 = 780 mmHg

P1V1 = P2V2 T1 T2 4

V2 = P1V1 T2 T1 P2

V2 = 760mmHg x 600cm3 x 323K ½ 298k x 780mmHg

= 633.7cm3 ½ (- ½ if units not given) 27 .a) When it does not lather with soap easily 1

b) Boiling 1 c) - Permit any one  1 - distillation - addition Na2CO3 28. a) They prevent air and water from coming in contact with the metals since theycoat the metal 1 b) Because the material used for galvanizing e.g. Zinc is more reactive than iron. Once scratched they form oxides which prevent rusting1

29. a) NH4Cl is soluble; NaHCO3 is insoluble  ½ Hence separated by filtration  ½

b) By ½ heating NaHCO3 which decomposes to Na2CO3 NaHCO3(s) Na2CO3(s) + H2O(l) + CO2

c) Ammonium chloride is reacted with slaked lime / calcium hydroxide Ca(OH)2(aq) + NH4Cl(aq) Cacl2(aq) + H2O(l) + NH3(g) 30. - Increasing pressure - Lowering temperature - Increasing concentration of reactants