Notes - Double Replacement Products TERMS Soluble - substances that can be dissolved in water. Insoluble - substances that cannot be dissolved in water. Precipitate - a substance that falls out of solution when it is one of the products of a reaction. Precipitates are insoluble in water. The symbol for a precipitate is ? and would be a solid (s) for the state of matter RULES In a double replacement reaction the metal parts of each reactant switch places. Write down the new products. Look up the new products in a table of solubilities. If a product is listed as being insoluble, this product is a precipitate. Write the symbol for a precipitate, ? , after any product that is listed in the table of solubilities as being insoluble.