Class 12 Record Experiment 6

 (Write in LHS)                     Experiment 6                          Preparation of Mohr s salt 

PREPARATION OF DOUBLE SALT OF FERROUS AMMONIUM SULPHATE  (MOHR S SALT )

(Write in RHS)                            

 Experiment 6                          

 Preparation of Mohr s salt 

AIM :- To prepare crystals of double salt of ferrous ammonium sulphate (mohr s salt) FeSO4(NH4)2SO46H2O

APPARATUS AND CHEMICALS

Two 250ml beakers, glass rod, china dish, funnel, filter paper, wash bottle, funnel stand, wire gauze, tripod stand and burner

7g of ferrous sulphate, 3.5g of ammonium sulphate, 1-2ml of dilute sulphuric acid, ethanol and distilled water.

THEORY

The additional compounds which are stable in solid state only but are broken down into individual constituents when dissolved in water are called double salts. Mohr s salt is double salt which is prepared by dissolving equimolar quantity of Ferrous Ammonium Sulphate and Ammonium Sulphate in minimum quantity of water containing dilute Sulphuric acid. The solution is filtered and heated in a china dish till point of crystallization is reached and then cooled to obtain light blue coloured crystal.

Chemical equations:

FeSO4.7 H2O  + (NH4)2SO4      →  FeSO4(NH4)2SO46H2O + H2O

PROCEDURE

1. Take a 250ml beaker and wash it with water. Transfer 7g of ferrous sulphate and 3.5g of ammonium sulphate crystals to it. Add about 2-3ml of dilute sulphuric acid to prevent the hydrolysis of ferrous sulphate

2. In another beaker boil about 20ml of water for about 5 minutes to expel dissolved air.

3. Add the boiling hot water to the contents in the first beaker in small instalments at a time. Stir with a glass rod until the salts have completely dissolved.

4. Filter the solution to remove undissolved impurities and transfer the filtrate to china dish.

5. Heat the solution in a china dish for some time to concentrate it to the crystallisation point

6. Place the china dish containing saturated solution over a beaker full of cold water. On cooling crystals of Mohr s salt separate out.

7. Decant off the mother liquor quickly. Wash the crystals in the china dish with a small quantity of alcohol to remove any sulphuric acid sticking to the crystals. 

8. Dry the crystals by placing them between filter paper pads.

(Write in LHS)  FERROUS AMMONIUM SULPHATE  (MOHR S SALT ) FeSO4(NH4)2SO46H2O

OBSERVATIONS

Weight of crystals obtained = …………g

Expected yield                         = ………..g

Colour of the crystals            = light green

Shape of the crystals             = Monoclinic

(Write in RHS)   Experiment 6                                  Preparation of Mohr s salt contd………….

PRECAUTIONS

1. Cool the solution slowly to get good crystals without disturbing.

2. Do not heat the solution for a long time as it may oxidize ferrous ions to ferric ions.

RESULT

Weight of crystals obtained = …………g

Expected yield                         = ………..g

Colour of the crystals            = light green

Shape of the crystals             = Monoclinic