To Separate sand and calcium carbonate

Experiment 2: TO SEPARATE SAND AND CALCIUM CARBONATE.

OBJECTIVE

TO SEPARATE SAND AND CALCIUM CARBONATE IN THE PURE AND DRY STATE FROM THE GIVEN MIXTURE OF SAND AND CALCIUM CARBONATE BY THE PHYSIOCHEMICAL METHOD.

APPARATUS REQUIRED

Porcelain basin, filter paper, glass rod, funnel, wash bottle, tripod stand and wire gauze.

CHEMICAL REQUIRED

A mixture of sand and CaCO₃, dil.HCl, Na₂CO₃, AgNO₃

THEORY

Both sand and CaCO₃ are insoluble in water but CaCO₃ is dissolved in mineral acid. When the mixture of Sand and CaCO₃ is treated with dil HCl, CaCO₃ is decomposed to give CaCl₂ solution while sand is unaffected.

Sand + CaCO₃ + 2HCl → Sand + CaCl₂ + CO₂ + H₂O

On filtration, the sand remains as residue while calcium chloride solution is obtained as filtrate. The sand is washed with water till it is free from Cl^– ion. Filtrate on treating with precipitating reagent as Na₂CO₃ solution produces a white precipitate of CaCO₃. The mixture is heated, and filtered and the residue is washed with hot water and then dried to get pure CaCO₃.

CaCl_{2}+Na_{2}CO_{3}\rightarrow \underset{White\ ppt.}{CaCO_{3}}+2NaCl

PROCEDURE

A mixture of sand and calcium carbonate of about 3 gm is taken in a beaker and dil HCl is added in minimum amounts till the evolution of CO2 is stopped. The reaction mixture is filtered and filtrate of the first time is collected in which residue contains sand. But Filtrate contains CaCl₂ solution. The residue is washed several times and the washed sand is dried. The filtrate is made slightly alkaline and then sodium carbonate solution is added The reaction mixture is warmed, and filtered and the precipitate of CaCO₃ is washed by water to get the free form of chloride ion. The presence of Cl^– is checked by the AgNO₃ solution. The precipitate is dried.

OBSERVATION TABLE

PURITY TEST FOR SAND (AgNO₃ test)

TEST REACTION

Cl^{-}+AgNO_{3}\rightarrow \underset{Curdy\ white\ ppt.}{AgCl}+NO_{3}^{-}

PURITY TEST FOR CaCO₃ [TEST FOR Cl^– and CO₃^—]

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

RESULT

Calcium carbonate was separated from the mixture of sand and calcium carbonate.

CONCLUSION

The mixture containing acid soluble and acid insoluble substances can be separated by dissolution followed by precipitation.

PRECAUTION

1. Precipitation should be completed.
2. CaCO₃ should be completely dissolved in dil. HCl.
3. Cl^– ion should be completely washed away.
4. The stem of the funnel should be touched with a beaker.