INTRODUCTION
PREPARATION OF MOHR’S SALT
aim:
To study Mohr’s salt.
THEORY:
Mohr’s Salt, also referred to as ammonium ferrous(II)
sulphate, is an inorganic compound that consists of two
primary cations - the ammonium cation (NH4+) and the
ferrous cation (Fe2+).It is categorized as a double salt of
ammonium sulphate and ferrous sulphate.
It is commonly used as a laboratory reagent. When
dissolved in water, it yields an aqua complex
[Fe(H2O)6]2+ which has an octahedral molecular
structure. Mohr’s Salt is named after the German
scientist Karl Friedrich Mohr who discovered it. Mohr's
salt has a molar mass of 392.21 g/mol and it appears as a
blue green solid.
STRUCTURE OF MOHR’S SALT:
Preparation:
Mohr's salt is prepared by dissolving an equimolar
mixture of hydrated ferrous sulphate and ammonium
sulphate in water; containing a little of sulphuric acid
and the crystallization from the solution. On
crystallization light green crystals of ferrous
ammonium; sulphate separate out.
Ferrous sulphate FeSO4.7H2O
Ammonium sulphate (NH4)2 SO4\
Mohr's Salt FeSO4-(NH4)2SO4.6H2O
MATERIALS REQUIRED:
Apparatus :
Two beakers, china dish, funnel, funnel stand, glass rod, wash
bottle, tripode stand, wire gauze, ferrous sulphate crystals,
ammonium sulphate crystals,dilute sulphuric acid.
CHEMICALS:
Before coating, steel sheet or rod is passed through sulphuric acid.
This treatment produces large quantities of iron(II) sulphate as a
by product. A little more sulphuric acid may be added to ensure
that the final solution remains slightly acidic.
Since ammonia solution is moderately alkaline, the change from
excess sulphuric acid to excess ammonia may be detected either
with an indicator eg:- litmus paper, or by measuring the pH of the
mixture with a pH meter.
PROCEDURE:
1. Take a clean 250ml beaker, transfer 7g of FeSO4 and 3.5g
of (NH4)2SO4 crystals to it. Add 2.3ml dilute H2SO4(to
prevent hydrolysis).
2. In another beaker boil 20ml H2O for 5 minutes(to expand
air).
3. Add boiling hot H2O to the content in small quantities. Stir
until salts have completely dissolved.
4. Filter it and heat the filtrate in a china dish till it
concentrate to crystallisation point.
5. Place the china dish over the beaker full of cold H2O, cool
it and collect the crystals.
Observation:
Weight =
Colour =
Result: