What type of reaction occurs when a soluble salt reacts to form a precipitate?

• A. Single displacement
• B. Double displacement
• C. Synthesis
• D. Decomposition

Answer: (B)

When soluble salts are dissolved, their ions are free in solution. If those ions swap partners and one of the new combos is insoluble, it will come out as a solid—the precipitate. This swapping of ions from two salts is a double displacement (metathesis) reaction, and the solid formed is the precipitate. For example, AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq) shows the ions pairing to form an insoluble product (AgCl) and a soluble one (NaNO3).

Other types don’t describe this exact situation: single displacement involves an element kicking another out of a compound, synthesis is two substances combining into one new substance, and decomposition is a compound breaking down into simpler substances.