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 an Na2SO41aq2 solution is added and a white precipitate forms. What is the identity of the unknown white solid?

Key Concepts

Solubility and Dissolution

Solubility refers to the ability of a substance to dissolve in a solvent, forming a solution. In this case, the white solid dissolves in water, indicating it is soluble. The solubility of ionic compounds varies; for example, barium chloride, lead chloride, and zinc chloride all have different solubility characteristics in water, which is crucial for identifying the unknown solid.

Precipitation Reactions

A precipitation reaction occurs when two soluble salts react in solution to form an insoluble solid, known as a precipitate. In this scenario, the addition of Na2SO4 results in a white precipitate, which suggests that one of the ions from the unknown solid reacts with sulfate ions to form an insoluble compound. Identifying the precipitate can help determine the identity of the original solid.

Ionic Compounds and Their Solubility Rules

Ionic compounds consist of positively and negatively charged ions. Their solubility in water is governed by specific rules; for instance, sulfates are generally soluble except for those of barium, lead, and calcium. Understanding these rules allows us to predict the behavior of the unknown solid when mixed with Na2SO4, leading to the identification of the solid based on the formation of a precipitate.