Principle: Coarse salt contains insoluble impurities such as sediment, as well as soluble impurities such as: Ca2, Mg2, SO42-, etc. Insoluble impurities can be removed by filtration. Ca2, Mg2, and SO42- in the soluble impurities can be removed by adding BaCl2, NaOH and Na2CO3 solutions to form a precipitate. It can also be removed by adding BaCO3 solid and NaOH solution, and then evaporating the water to obtain Purer refined salt.

Steps: Dissolution: (Weigh about 4 grams of coarse salt and add it to a 12ml beaker) Stir with a glass rod to accelerate dissolution. The liquid is turbid and contains sediment

Filtering: Adjust the iron ring to the appropriate position and place the beaker and filter. The glass rod is placed against the three layers of filter paper. The lower end of the funnel is placed against the inner wall of the beaker. The mouth of the beaker is placed against the glass rod for drainage. The edge of the liquid level is lower than the edge of the filter paper (the filter paper should be close to the funnel when making the filter). If the filtrate is turbid Can be filtered again.

The clear filtrate is filtered out and the insoluble matter is left on the filter paper

Add HCl first and then add excess BaCl2

A white precipitate of BaSO4 appears↓

BaCl2 NaSO4= BaSO4↓ NaCl

Filter and add excess Na2CO3

A white precipitate BaCO3↓CaCO3↓ appears

Na2CO3 BaCl2= BaCO3↓ NaCl

Na2CO3 Ca(OH)2= CaCO3↓ H2O CO2↑

Filter and then add excess NaOH

A white precipitate of Mg(OH)2↓ appears

NaOH MgCl2= Mg(OH)2↓ NaCl

Filter and then add HCl

Bubbles out

HCl Na2CO3= NaCl H2O CO2↑

HCl NaOH= NaCl H2O

Experimental conclusion: Coarse salt contains not only insoluble substances such as sediment, but also soluble substances such as MgCl2 BaCl2 sulfate.