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1989 WAEC Chemistry Practical (a) A mixture consist of sodium chloride, ammonium chloride and lead (II) tetraoxosulphate (VI). Describe...

Chemistry
WAEC 1989

(a) A mixture consist of sodium chloride, ammonium chloride and lead (II) tetraoxosulphate (VI). Describe how you would obtain each component in a pure state.

(b) You are required to determine the concentration of a solution of tetraoxosulphate (VI) acid by titrating it against sodium trioxocarbonate (IV) solution of known concentration.

(i) Name the indicator you would use 

(ii) List two precautions you would take to ensure accurate readins

(iii) State the colour of the sodium trioxocarbonate (IV) solution after adding the named indicator and then at the end point. 

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Explanation

(a) Heat the mixture. Ammonium chloride is sublime and collected in the cold upper part of the test-tube. The resulting solid is cooled and stirred with water to dissolve sodium chloride. Filter, wash, and dry the residue to obtain lead (lI) tetraoxosulphate (VI). Evaporate the filtrate to dryness to obtain sodium chloride crystals.

 

(b)(i) Methyl orange (or phenolphthalein)

(ii) Any two of the following;

- Ensure that there are no air bubbles in the burette

- Read off burette at eye level

- Ensure that burette is not leaking

- Rinse the conical flask with distilled water

- Take three concordant readings.

(ii) with methyl orange: yellow \(\to\) pink/orange with phenolphthalein: pink \(\to\) colourness.


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