Estimation of Barium as Barium Chromate (BaCrO₄)

 Estimation of Barium as Barium Chromate (BaCrO₄)

Aim

To estimate the amount of barium present in the given solution by gravimetric method by precipitating it as barium chromate (BaCrO₄).

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Principle

Barium ions react with potassium chromate in slightly acidic medium to form a yellow insoluble precipitate of barium chromate (BaCrO₄).

The precipitate is filtered, washed, dried and weighed. From the weight of BaCrO₄ obtained, the amount of barium present in the sample is calculated.

Reaction

$$Ba^{2+} + CrO_4^{2-} \rightarrow BaCrO_4 \downarrow$$

The precipitate BaCrO₄ is yellow and insoluble in water.

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Requirements

Chemicals

Given barium solution

Potassium chromate (K₂CrO₄) solution
Acetic acid
Distilled water

Apparatus

Beaker

Glass rod
Funnel
Filter paper / Gooch crucible
Porcelain crucible
Oven / hot plate
Desiccator
Weighing balance

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Procedure

1. Take 25 mL of the given barium solution in a beaker.

2. Add a few drops of acetic acid to make the solution slightly acidic.

3. Heat the solution gently.

4. Add potassium chromate solution slowly with constant stirring.

5. A yellow precipitate of barium chromate (BaCrO₄) forms.

6. Heat the mixture for a few minutes to allow the precipitate to settle.

7. Filter the precipitate through filter paper or a Gooch crucible.

8. Wash the precipitate with warm distilled water until free from impurities.

9. Dry the precipitate in an oven, cool in a desiccator and weigh.

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Observation Table

Sr. No.	Observation	Value
1	Weight of empty crucible	W₁ g
2	Weight of crucible + BaCrO₄	W₂ g
3	Weight of BaCrO₄ obtained	(W₂ − W₁) g

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Calculation

Molecular weight of BaCrO₄ = 253.3 g/mol
Atomic weight of Ba = 137.3 g/mol

$$\text{Weight of Ba} = \frac{137.3}{253.3} \times (W_2 - W_1)$$

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Result

The amount of barium present in the given solution was determined gravimetrically as barium chromate (BaCrO₄).