Problem: You are presented with a white solid and told that due to careless labeling it is not clear if the substance is barium chloride, lead chloride, or zinc chloride. When you transfer the solid to a beaker and add water, the solid dissolves to give a clear solution. Next a Na2SO4(aq) solution is added and a white precipitate forms.What is the identity of the unknown white solid?

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Na2SO4(aq)

▪ sodium → group 1A → +1 charge → Na+
 ▪ sulfate → polyatomic ion → -2 charge → 
SO4


• group 1A ions are soluble with everything → Nawill not precipitate

• find a cation (positively charged ion) that is insoluble with SO42–

Sulfates (SO42-) are soluble except those of Ca2+, Sr2+, Ba2+, Ag+, and Pb2+

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Problem Details

You are presented with a white solid and told that due to careless labeling it is not clear if the substance is barium chloride, lead chloride, or zinc chloride. When you transfer the solid to a beaker and add water, the solid dissolves to give a clear solution. Next a Na2SO4(aq) solution is added and a white precipitate forms.

The figure shows three beakers with a solid in the first beaker, with a solution in the second beaker, and with a solution with a precipitate in the third one. There is a right arrow labeled as add H2O between the first and the second beakers. There is a right arrow labeled as add aqueous Na2SO4 between the second and the third beakers.


What is the identity of the unknown white solid?

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Based on our data, we think this problem is relevant for Professor Carlon's class at UCB.