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B. Sc. (3rd Sem) Honours with Chemistry BCHE-602 (Inorganic Chemistry Practicals-II) L

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Continuous evaluation 30

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End semester exam 20 Total marks 50 Credits 2.0

Course Objectives: To develop skills in the synthesis and quantitative analysis by doing titrations in different branches of inorganic chemistry. (A) Iodo / IodimetricTitrations (i) Estimation of Cu(II) and K2Cr2O7 using sodium (ii) (iii)

thiosulphate solution (Iodimetrically). Estimationof(i)arseniteand(ii)antimonyintartaremeticiodimetrically Estimation of available chlorine in bleaching powderiodometrically.

(B) Inorganic preparations (i) Cuprous Chloride,Cu2Cl2 (ii) Preparation of Manganese(III) phosphate,MnPO4.H2O (iii) Preparation of Aluminium potassium sulphate KAl(SO4) 2.12H 2O (Potash alum) or Chromealum.

What is Potash alum? Potash alum is also called potassium aluminium sulfate is a chemical compound commonly encountered as the dodecahydrate. It is a double salt widely used in medicine and in the water purification process. Potash alum is not a complex salt. The chemical formula of potash alum is K2SO4.Al2(SO4)3.24H2O.

Aim: To prepare potash alum from potassium sulfate and aluminium sulfate through crystallization.

Theory:

The formula for potash alum is K2SO4.Al2(SO4)3.24H2O. It is prepared by crystallizing the alum from a concentrated solution containing equimolar amounts of potassium sulfate and aluminium sulfate. It is a colourless, crystalline solid with a sour taste. The crystal of potash alum is octahedral in shape. It is commonly known as ‘fitkari’. The chemical reaction is given below. K2SO4(aq) + Al2(SO4)3(aq) → K2SO4.Al2(SO4)3.24H2O(s) (Potash Alum) While dissolving aluminium sulphate in warm water a little amount of dilute sulfuric acid is added in order to prevent the hydrolysis of this salt. When a solution containing two inorganic salts in a definite proportion is allowed to crystallize a double slat is said to have separated. The name alum is given to the special series of double salts. Aluminium is the most abundant metal and the recycling of aluminium products by melting and recasting into other metal products are used in the production of various aluminium compounds. In that one of the most useful compounds is potash alum.

Materials Required: 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.

Potassium sulphate Aluminium sulphate Dil. sulfuric acid Distilled water Beaker Conical flask Tripod stand Funnel Burner China dish Wire gauze Filter paper

Apparatus Setup:

Laboratory Preparation of Potash Alum from Aluminium Sulphate and Potassium Sulphate

Procedure: 1.

Weigh 12.5g of potassium sulfate and dissolved in a minimum quantity of distilled water in a beaker. Stir to dissolve the crystals. 2. Take a conical flask, in that dissolve 50g of aluminium sulfate in warm water and add 3ml of dilute sulfuric acid to make the solution clear. 3. Filter the solutions if it is not clear. 4. Mix the two clear solutions in a china dish. 5. Place the china dish on a wire gauze over a burner. 6. Stir the solution and concentrate the solution till the crystallization point is reached. 7. Place the solution over a beaker containing cold water for a few hours. 8. Crystals of potash alum will get separated, filter then from the mother liquor and wash them with a small quantity of cold water. 9. Dry the crystals by pressing gently between the folds of the filter paper. 10. Weigh them on the chemical balance to know the yield.

Observations: Colour of the crystal

Colourless

Shape of the crystal

Octahedral

Solubility in water

Soluble

Action of blue litmus paper

Blue litmus turns red

Results and Discussion: 1. 2.

The yield of Potash alum is _______ gm. Expected yield is ______ gm.

Precautions: 

To prevent hydrolysis of aluminium sulfate, dilute sulfuric acid should be added while preparing the saturated solution.

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During crystallization do not disturb the solution.

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For dissolving salts always use warm water.

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The concentrated solution should be cooled slowly....