**Determine the equivalent mass and number of molecules of water of crystallisation in a sample of Mohr’s salt FeSO**_{4} (NH_{4})_{2} SO_{4}.nH_{2}0. Provided N/20 KMnO_{4}

_{4}(NH

_{4})

_{2}SO

_{4}.nH

_{2}0. Provided N/20 KMnO

_{4}

Chemistry Lab ManualNCERT Solutions Class 12 Chemistry Sample Papers

**Determine the equivalent mass and number of molecules of water of crystallisation in a sample of Mohr’s salt FeSO _{4} (NH_{4})_{2} SO_{4}.nH_{2}0. Provided N/20 KMnO_{4}**

**Chemical equations**

**Theory**

Normality of ferrous ammonium sulphate can be determined by directly titrating it against standard (N/20) KMnO_{4} solution.

Eq. mass = Strength/normality

Substituting the value of strength and value of normality as calculated above, the equivalent mass of Mohr’s salt can be calculated. Suppose it comes out to be E.

Since Eq. mass of mohr’s salt is equal to its molecular mass, therefore molecular mass of Mohr’s salt is also equal to E.

**Indicator**

KMnO_{4} is a self-indicator.

**Endpoint**

Colourless to permanent pink (KMnO_{4}in burette).

**Procedure**

- Rinse and fill the burette with N/20 KMnO
_{4}. solution. - Weigh exactly 4.90 g of Mohr’s salt and dissolve in water to prepare exactly 250 ml of solution using a 250 ml measuring flask. Rinse the pipette with the prepared Mohr’s salt solution and pipette out 20.0 ml of it in a washed titration flask.
- Add one test tube (~ 20 ml) full of dilute sulphuric acid (~ 4 N) to the solution in titration flask.
- Note the initial reading of the burette.
- Add KMnO
_{4}solution into the titration flask from the burette till a permanent light

pink colour is imparted to the solution in the titration flask on addition of a last single drop of KMnO_{4}solution. - Note the final reading of the burette.
- Repeat the above steps 4-5 times to get three concordant readings.

**Observations**

**Calculations**