Preparation of Potash Alum

Formula

Potash alum's chemical formula is

• KAl(SO4)2
• AlK(SO4)2

Potash alum contains potassium, aluminium, and sulphate ions in 1:1:2 ratio.

Structure

Chemical formula

• The chemical formula for potash alum is KAl(SO4)2.
• It is usually produced in its hydrate form, which has 12 molecules of water attached to it.
• It is also known as the dodecahydrate form of potash alum. AlK(SO4)2X 12H2O is the chemical formula in this form.
• The formula can also be written as K2SO4.Al2(SO4)3.24 H2O. in its double sulphate form.

Applications of Alum

• Potash alum is quite useful as an antiseptic and astringent, especially after shaving.
• It is used as a catalyst in laboratories.
• It was used to purify water by settling dissolved sediments.It is widely used in India, particularly in small cities, villages, and towns.
• It is also used in the dyeing and printing of fabrics.

Preparation

• Potash alum has been obtained from alum-K, a naturally occurring sulphate mineral.
• However, due to increased production and usage, it is also produced on an industrial scale.

Raw materials required:

Following materials are required:

• Aluminum sulphate
• Sulphuric acid
• Potassium sulphate
• Distilled water

Apparatus Required

• Bunsen burner
• Watch glass
• Funnel glass and stand
• Beakers
• Evaporating dish
• Tripod stand
• Stirring rod
• Porcelain plate
• Wire gauze
• Measuring cylinder
• Filter paper

Potash Alum Preparation

• To begin, take 5g of potassium sulphate.
• Then, after properly weighing it, powder it.
• After powdering, transfer the potassium sulphate powder to a 150 ml beaker.
• Add approximately 20ml of water to the beaker and continuously stir.
• If the solution does not become clear, it can be slightly warmed.
• Set aside the solution.
• Add 20g of powdered aluminium sulphate to a second beaker of similar size.
• Fill this beaker with 30ml of distilled water.
• Add about 2ml of concentrated sulphuric acid.
• To make a clear solution, continuously stir the solution with a glass rod.
• If the aluminium sulphate does not dissolve properly in water, you can warm the solution and add a small amount of extra sulphuric acid.
• We also require a clear solution in this beaker.
• Pour the two prepared solutions into a china dish after passing them through a filter paper.
• It aids in the separation of the solution's undissolved components.
• Set up the Bunsen burner and a tripod stand.
• Place the wire gauze over the evaporating china dish.
• Warm the solution and stir it frequently.
• Continue heating the solution until the crystallisation point is reached.
• Take the stirring rod out of the china dish and blow some air on it to check for the crystallisation point.
• The formation of a crystalline crust on the glass rod after blowing air indicates that the crystallisation point has been reached.
• Remove the dish from the heat.
• Place it over cold water after covering it with a watch glass.
• Wait until alum crystals form in the solution.
• After the crystals have formed, filter them from the mother liquor.
• Wash them with 5 - 6 ml of ice cold distilled water.
• Allow the washed crystals to dry by pressing them between filter papers.
• Your alum is prepared.
• Now, weigh the finished product.
• Record your findings.

The procedure is based on the chemical equation shown below:

Equation 1: Potash Alum Yield Calculation

Equation 2: Percentage Yield Calculation

• We know the experimental yield because we weighed the finished product at the end of the procedure.
• To calculate theoretical yield, we must first determine how many moles of potash alum were prepared during the experiment.
• Because potassium sulphate and aluminium sulphate combine in an equimolar ratio, moles of potash alum are equal to moles of reactants.
• We now know that the number of moles is equal to the ratio of actual grams to the compound's gram molecular weight.
  
  

Equation 3: Number of Moles

As a result, we need to know the gram molecular weight of three compounds in this experiment.

We can calculate the number of moles using equation 3 as shown below:

• We started with slightly more aluminium sulphate.
• But because potassium sulphate will be the limiting reagent, we should get 0.029 moles of alum from this experiment.
• We can convert the number of moles into grams using the formula below.

Potash alum weight = number of moles x gram molecular weight = 0.029 x 948.76 = 27.51 grams

We can now calculate the percentage yield of this experiment using the experimental yield to theoretical yield ratio.