Gravimetry Analysis Part-4: Solution based Problems and MCQ with Answers

SOLUTIONS PROBLEM IN GRAVIMETRY :-

  • Process carried out in dilute solution.
  • Reagents mixed slowly with constant stirring.
  • Ppt carried in hot solution if stability permits
  • Advantage of heating :- solubility is increases, reduction in degree of supersaturation, coagulation occur
  • Crystalline ppt digested as long as possible.
  • Ppt should be washed with dilute solution of electrolytes.
  • If contamination high re- dissolve in appropriate solvent and then re ppt for purity.

Digestion of precipitation :-  Digestion is a process keeping the precipitation within the mother liquor for a certain period of time to encourage densification of nuclei.

During digestion, small particle dissolve in larger one grow

This process help  produce larger crystal that are more easily filtered from solution.

IMPURITIES IN PRECIPITATION :-

Co- precipitation :– The simultaneous precipitation of more than one compound from a solution.

Inclusion :- it is crystallographic defect.

Example :- In NaCl crystsl Na  is replaced by k produced kcl.

If positive error occur due to inclusion so weight of ppt is increase.

If negative error occur due to inclusion so weight of ppt is decrease.

Occlusion :– occur when foreign ions get trapped in growing crystal

Mechanical Entrapment :- small amount of solution is entrapped.

Both occlusion and Entrapment are at minimum when the rate of ppt is low.

Surface adsorption :- Impurities are adsorption on the surface of ppt.

Post precipitation :-  It is the precipitation that occur as a layer upon the already formed precipitate.

Post precipitation always give positive error.

MCQ

1. Impurity are absorbed in surface of the ppt is called

A. Inclusion

B. Mechanical Entrapment

C. Surface adsorption

D. Post precipitation

2.  Crystal graphic defect is called as

A. Inclusion

B. Mechanical Entrapment

C. Surface adsorption

D. Post precipitation

3. Which error gives always positive error ?

A. Inclusion

B. Mechanical Entrapment

C. Surface adsorption

D. Post precipitation

4. Inclusion error is give

A. Positive error

B. Negative error

C. A and B

D. None of the above

5. when foreign ions get trapped in growing crystal  is called

A. Inclusion

B. Mechanical Entrapment

C. Surface adsorption

D. Occlusion

6. Which sentence is false about heating solution ?

A. Increase solubility of the solution

B. Increase degree of supersaturation.

C. Decrease degree of supersaturation

D. All of the above

7. Which sentence is  true about digestion ?

A. It is produced difficult in filtration

B. It is produced small ppt

C. It is produced larger ppt

D. All of the above

Answer key

1. C

2. A

3. D

4. C

5. D

6. B

7. C

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