Question: How do we know what ions are present in a solution?

What’s a solution? A liquid mixture of solute (solid) dissolved in solvent (liquid). Note: Most of the H+ and OH- combine to form H2O.

Some compounds aren’t very soluble Some compounds are relatively insoluble in water and therefore can help us identify them in solution. There are some rules to help us identify which compounds are insoluble. We use subscripts to help us identify the status of compounds in solution. e.g. NaCl(s)  Na(aq) + Cl(aq) (s) Means the substance is a solid (l) Means the substance is a liquid (g) Means the substance is a gas. (aq) means a solid substance is dissolved in solvent. H2O(l)

Solubility rules. All sodium, potassium and ammonium salts are soluble All nitrates are soluble. All chlorides are soluble except silver chloride; lead chloride is slightly soluble. All sulfates are soluble except for lead sulfate and barium sulfate; calcium sulfate and silver sulfate are slightly soluble. All carbonates and hydroxides are insoluble except those of sodium, potassium and ammonium; calcium hydroxide is slightly soluble.

Predicting precipitates: When ions dissolve the ions are separate and free to move, but ions can bump into each other and if the combination of ions happens to be insoluble a precipitate will form, and you will see a solid forming AgNO3(aq) + NaCl(aq)  AgCl(s) + NaNO3(aq) When AgNO3 was dissolved in water Ag is more attracted to water therefore it dissolves. When mixed with NaCl the silver ions are more strongly attracted to the Chloride ions therefore they bind together to form a solid.

Predicting precipitates: The actual equation happens between silver and chloride ions Ag+(aq) + Cl-(aq)  AgCl(s) The sodium ions and nitrate ions take no part in the reaction, and they are called spectator ions because they just sit back and watch.