Page 234 - Chemistry

(b) - Addition of Na 2CO 3(s)
- Addition of Ca(OH) 2(s)
- Addition of aqueous ammonia (award 1mk each for any two; Total =2mks)
2+
6. – Provides essential minerals e.g. Ca for strong bornes and teeth 1
- It has a better taste

7. a) The acid is water H 2O
Reason H 2O has donated a proton (H+)
2-
+
b) 2H (g) + CO 3 (aq) ___________ CO 2(g) + H 2O (l)
8. Magnesium carbonate reacts w ith rain water
o Containing caborn (iv) oxide dissolved.
o Forming magnesuin hydrogencarbonate
o Or MgCO 3(s) + CO 2(g) + H 2O (l) + Mg (HCO 3) 2 (aq)

9. (a) Lead ions  1
(b) Lead (II) hydroxide  1
(c) [Pb(OH) 4] 2-  1

10. a) Solubility of a salt is mass of a salt that dissolves in 100g of water at a given temperature. √1
b) Mass of Q that crystallizes out = 19.0 – 7.4 √ ½ = 11.6 g.
Mass of R that crystallizes out = 33 – 20.7 √ ½ = 12.3g.
Total mass of crystals = 12.3 + 11.6 √ ½ = 23.9g √ ½

11. Mass of dry salt = 16.86 – 15.86 √ ½
= 1.00g √ ½
Mass of water = 26.86 – 16.86 = 10g√ ½
Mass of salt in 60g of water = 60x1 = 6 g √ ½
10
12. (a) This is the maximum mass of a salt that will dissolve in 100g of water of a given
temperature
3
(b) 15g dissolve in 25cm water
3
? dissolve in 2100cm water
= 15 x 100 = 60g/100gwater
25
(c) (i) in graph paper
(ii) Every point on the solubility curve is a saturated point of a solution which contains a
maximum amount of salt X at a graph temperature
(iii) I 16g 
II 25g 
(iv) 25 – 16 = 9g/100g water 
(v) - Extraction of Na 2co 3 from Lake Magadi

- Extraction of Nacl from sea water

13. Add Methyl benzene to the mixture and stir to dissolve iodine. Filter and crystallize the
filtrate to obtain sodium chloride crystals.

14. (a) (ii) 72g /100g water  1.0
3
(iii) 100cm dissolve 72g
3
1000cm dissolve = (1000 x 72)
 ½
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