Question

to prepare a crystal of Mohr salt.. ​

Answer 1

Answer:

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Answer 2

Explanation:

Ferrous Ammonium Sulphate is also called Mohr’s salt a light green color sand like crystalline solid. It is a hazardous substance and preparation of ferrous ammonium sulfate is carried out from equimolar mixture of hydrated ferrous sulphate and ammonium sulphate in water; containing a little of sulphuric acid.

Aim

To prepare Mohr’s salt: ferrous ammonium sulphate from ferrous sulfate and ammonium sulfate in the presence of acid.

Theory

The formula for ferrous ammonium sulfate is FeSO4.(NH4)2SO4.6H2O. It is prepared by dissolving equimolar mixture of hydrated ferrous sulfate and ammonium sulfate in water containing a little sulfuric acid. The solution is subjected to crystallization, ferrous ammonium sulfate separates out from the solution.

The chemical reaction is given below.

FeSO4 + (NH4)2SO4 + 6H2O → FeSO4.(NH4)2SO4.6H2O (Mohr’s salt)

The addition of sulfuric acid in this experiment prevents the hydrolysis of this salt. Ferrous ammonium sulfate is a pale green crystalline compound which does not effloresce like ferrous sulfate. It is less readily oxidised than FeSO4 and therefore, a better volumetric reagent in preference to ferrous sulfate.

Mohr’s salt is also called as double salt which contain more than one simple salt. It undergoes complete dissociation in aqueous solutions. Mohr’s salt dissociates into Fe2+, NH4+, SO42- ions and give their individual chemical test.

Mohr’s salt is light green transparent octahedral crystals. It is soluble in water giving acidic solution which turns blue litmus paper red and gives effervescence with sodium bicarbonate evolving carbon dioxide.

Ferrous Ammonium Sulphate also called mohr’s salt is prepared by dissolving equimolar mixture of hydrated ferrous sulphate and ammonium sulphate in water containing a little sulphuric acid. The solution is subjected to crystallization.

Materials Required

Conical flask

Tripod stand

Burner

Funnel

Watch glass

Glass rod

Filter paper

Wire gauze

China dish

Ferrous sulfate

Ammonium sulfate

Dilute sulphuric acid

Apparatus Setup

Preparation of Ferrous Ammonium Sulphate (Mohr's Salt)

Laboratory Preparation of Ferrous Ammonium Sulphate – Mohr’s Salt

Procedure

Weigh 7g of ferrous sulfate and 3.5g of ammonium sulfate separately.

Mix ferrous sulfate and ammonium sulfate in water in a beaker containing dilute sulphuric acid.

Gently warm the solution in order to get a clear solution.

Filter the solution in order to remove suspended impurities and concentrate the clear filtrate by heating it china dish over a sand bath till the crystallization point is reached.

Stir the solution occasionally during heating.

Keep the solution undisturbed for slow cooling. After some time crystal of ferrous ammonium sulfate will get separated from the solution.

Separate the crystals by decantation from the mother liquor and wash the crystals with cold water.

Dry the crystals between the folds of filter paper or by spreading on a porous plate.

Observations

Colour of the crystal Light green

Shape of the crystal Octahedral

Solubility in water Soluble

Action of blue litmus paper Blue litmus turns red

Results and Discussion

The yield of ferrous ammonium sulfate or Mohr’s salt is _______ gm.

Precautions

Allow slow cooling and do not disturb the solution during cooling in order to get good quality crystals.

During the process heating of the solution should be done in a short time only. Because prolonged heating forms ferric ions along with ferrous ammonium sulfate.

Suppose if the solution is yellow instead of green the experiment should be repeated.