Precipitation reaction between barium chloride and dilute sulphuric acid

Experiment 3: PRECIPITATION REACTION BETWEEN BARIUM CHLORIDE AND DILUTE SULPHURIC ACID.

OBJECTIVE

TO CARRY OUT THE PRECIPITATION REACTION BETWEEN BARIUM CHLORIDE AND DILUTE SULPHURIC ACID AND TO OBTAIN THE PRECIPITATE IN A PURE AND DRY STATE.

APPARATUS REQUIRED

1. beaker
2. test tube
3. filter paper
4. funnel
5. glass rod
6. burner

CHEMICAL REQUIRED

1. BaCl₂ solution
2. Dilute H₂SO₄
3. AgNO₃ solution

THEORY

The reaction in which partner radicals are exchanged and thereby water-insoluble compound formed from a water-soluble compound is called a precipitation reaction.

When sulphuric acid is added to the barium chloride solution, a white ppt of barium sulphate is obtained.

BaCl_{2}+H_{2}SO_{4}\rightarrow BaSO_{4}+2HCl

The purity of the precipitate can be checked by treating the ppt-washed water with a few drops of AgNO₃ solution and BaSO₄ solution separately. The presence of chloride and sulphate ions is indicated by the formation of a white ppt. respectively with these two reagents.

PROCEDURE

A test tube full of barium chloride solution was taken in a beaker and warmed slightly. Dilute sulphuric acid was added a little at a time with constant stirring of the mixture with the help of a glass rod. A white precipitate was formed. The precipitate is allowed to settle down at the bottom of the beaker. The upper layer formed was a clear solution known as a supernatant liquid.

A few drops of sulphuric acid are added carefully along the side of the beaker to check the completeness of precipitation. If it is not completed, a precipitate will be formed as soon as sulphuric acid touches the upper clear solution (supernatant liquid). In such cases, more sulphuric acid has to be added.

When precipitation is completed, the solution was filtered. The precipitate was washed some time with water by decantation. The last drops of filtrate were washed with silver nitrate and barium chloride solution to confirm that the precipitate was free from soluble chloride and sulphate. Finally, the precipitate was transferred onto the filter paper. The precipitate was dried carefully on asbestos placed over a tripod stand with the help of a burner.

OBSERVATION TABLE [COMPLETENESS OF PRECIPITATE]

TEST OF PURITY OF PRECIPITATE

TEST REACTION

\begin{align*}
CO_{3}^{--} +BaCl_{2} &\rightarrow  \underset{white\ ppt.}{BaCO_{3}} +2Cl^{-}\\
Cl^{-}+AgNO_{3} &\rightarrow \underset{white\ ppt.}{AgCl}+NO_{3}^{-}
 \end{align*}

RESULT

Hence, the precipitate of Barium Sulphate was obtained in the pure and dry state.

CONCLUSION

Precipitate of pure and dry Barium sulphate can be obtained by treating BaCl₂ solution with dilute H₂SO₄ solution followed by washing and drying.

PRECAUTIONS

1. The precipitation should be complete.
2. During washing by decantation, there should not be loss of the precipitate.
3. All the glassware should be handled with care.