Preparation of Potash Alum
Potash alum's chemical formula is
Potash alum contains potassium, aluminium, and sulphate ions in 1:1:2 ratio.
- 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.
- 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
- Bunsen burner
- Watch glass
- Funnel glass and stand
- 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.