### 1993 WAEC Chemistry Practical (a) State; (i) One advantage: (ii) One disadvantage of evaporation of salt solutions to dryness...

WAEC 1993

(a) State;

(ii) One disadvantage of evaporation of salt solutions to dryness over crystallization.

(b)(i) List two normal salts which when dissolved in pure water are acidic to litmus

(ii) Mention the phenomenon that accounts for the behaviour of the salts in (b)(i) above.

(c)(i) Outline a suitable laboratory method for separating a mixture of glucose and starch.

(i) Give two chemical tests that would enable you to identify three solids suspected to be glucose, sucrose and starch.

##### Explanation

(a)(i) Faster rate of obtaining product

(ii) Product is less pure. There is risk of decomposition of product.

(b)(i) NH$$_4$$Cl, FeCl$$_3$$, AlCl$$_3$$, CuSO$$_4$$, FeCl$$_2$$, NH$$_4$$NO$$_3$$, etc (any two)

(ii) Hydrolysis

(c)(i) Add distilled water, stir and filter, the filtrate obtained is glucose while the residue is startch

 (ii) Add fehling's solution to a solution suspension of each sample Bricks - red ppt. formed  No visible reaction Sample is starch  Sample is glucose or sucrose Add few drops of iodine soln. to a solution/suspension of each sample Blue - black colouration  No visible reaction Sample is starch  Sample is glucose or sucrose