Chem question

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2010-04-24 7:17 pm

Smithsonite (or zinc carbonate) is a mineral ore of zinc. It reacts with nitric acid to give a salt A which can be used to set dyes on fabrics in the dyeing industry. The procedures for preparing the salt A from Smithsonite are as follows:
Stage 1: Dissolve small portions of powdered Smithsonite in 100.0 cm^3 of 1.0M nitric acid in a beaker with constant stirring, until it is in excess.
Stage 2: Filter the solution from Stage 1 to get a clear aqueous solution of salt A.
Stage 3: Evaporate the filtrate from Stage 2 to obtain the crystals of salt A.

Question:
Why is it necessary to have Smithsonite added in excess?

回答 (1)

[匿名]

2010-04-24 9:53 pm

✔ 最佳答案

The smithsonite should be excess because the excess insoluble smithsonite can be easily removed by filtering. After filtering, there will be no nitric acid left hence a pure zinc nitrate solution can be obtained. If the nitric acid is in excess, the zinc nitarte solution will have some nitric acid as impurity beacuse the excess nitric could hardly be removed.

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