Page 237 - Chemistry

3
(ii) Moles of NaCl in 25cm
Mole ratio is 1 : 1
Moles of NaCl = 0.0024 moles1 (1 mk)

3
(iii) Moles of NaCl in 500 cm
3
If 25cm = 0.0024 moles
3
∴ 500 cm = ?
3
= 500 cm 1 x 0.0024 moles
3
25 cm
= 0.048 moles 1 (2 mks)

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(iv) Mass of NaCl in 10cm
Mass = moles x R.F.M.
= 0.048 x 58.5 = 2.808g

(v) Mass of water = mass of solution – mass of NaCl
= (10.70 – 2.808)g 1
= 7.892 g 1 (2 mks)

(vi) If 7.892 of H 2O 2.808g 1
100g of H 2O ?
100g x 2.808 1
7.892g
= 35.6g /100g of H 2O1

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20. Add 100cm of 2M √ potassium hydroxide or 200cm3 of 1M potassium hydroxide to the acid.
Heat the solution until it is saturated and cool to obtain crystals. Dry the crystals between
filter papers

21. (a) 139g of solution contains 39g solute
90kg of solution contains 39 x 90 = 25.25g
139
Mass of solvent = 90 – 25= 64.75g
o
(b) 80 C

22. (a) Calcium hydrogen carbonate/Magnesium hydrogen carbonate;
(b) Water boils off and is condensed leaving the salt;
(c) Provides minerals used to strengthen bones

23. (a) Delivery tube should not dip into solution
- Thistle funnel should did into the solution
- Gas jar was no water/ little water in trough ( 1 each max 2)
(b) Oxygen

24. a) acidity water with Nitric add aqueous lead nitrate or
- silver nitrate formation of white precipitates shows presence
penalize fully for uric acid 1 ½ mk of chloride ions
2+
b) provide essentials minerals e.g. Ca ions

25. a) I- Cu (OH) 2 or copper (II)hydroxide√1
2+
b) Cu(NH 3) 4 √1
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