Salts

Making soluble salts You need to be able to describe the reactions of acids with bases and metals. You should be able to work out the particular salt formed in the reaction.  

Acids and bases When acids react with bases, a salt and water are made: acid + metal oxide → salt + water acid + metal hydroxide → salt + water Remember that most bases do not dissolve in water. But if a base can dissolve in water, it is also called an alkali.

Reactive metals Acids will react with reactive metals, such as magnesium and zinc, to make a salt and hydrogen: acid + metal → salt + hydrogen The hydrogen causes bubbling during the reaction, and can be detected using a lighted splint.

Naming saltsThe name of the salt produced in a neutralization reaction can be predicted.The first part of the name is 'ammonium' if the base used is ammonia.Otherwise, it is the name of the metal in the base.the second part of the name comes from the acid used: Chloride (if hydrochloric acid is used) Nitrate (if nitric acid is used) Sulfate (if sulfuric acid is used) Examples:Hydrochloric acid + Copper oxide → Copper chloride + waterSulfuric acid + Sodium hydroxide → Sodium sulfate + water

Ammonia salts Many artificial fertilisers are ammonium salts, made by the reaction of an acid with ammonia solution. For example:       Acid                               Alkali                                Fertiliser    Nitric acid              Ammonia solution                 Ammonium nitratePhosphoric acid        Ammonia solution                 Ammonium phosphate  Sulfuric acid          Ammonia solution                 Ammonium sulfate

Crystallising salt solutions You may be asked to describe how to make a soluble salt.If the base dissolves in water, you need to add just enough acid to make a neutral solution.Check a small sample with universal indicator paper.If ammonia solution is used, you can add a little more than needed to get a neutral solution.Warm the salt solution to evaporate the water. You get larger crystals if you evaporate the water slowly.

Copper oxide, and other transition metal oxides or hydroxides, do not dissolve in water.If the base does not dissolve in water, you need an extra step.You add the base to the acid until no more will dissolve and you have some base left over (called an excess).You filter the mixture to remove the excess base, then evaporate the water in the filtrate to leave the salt behind.

Making insoluble salts Insoluble salts do not dissolve in water. They can be made by mixing appropriate solutions of ions together. Soluble and insoluble salts Soluble                                                         InsolubleAll nitrates                                                      NoneMost sulfates                                                  Lead sulfate, barium sulfateMost chlorides, bromides and iodides               Silver chloride, silver bromide,                                                                      silver iodide, lead chloride,                                                                     lead bromide, lead iodideSodium carbonate, potassium carbonate          Most other carbonatesSodium hydroxide, potassium hydroxide          Most other hydroxides

Notice that all nitrates and most chlorides are soluble. This is why many of the chemicals you use in the laboratory are nitrates or chlorides. If you want to make an insoluble salt, you can react together two soluble salts in a precipitation reaction.

Making an insoluble salt Silver chloride is insoluble - you can see this from the table. You need a soluble silver salt and a soluble chloride salt to make it. Silver nitrate and sodium chloride are both soluble. When you mix their solutions together, you make soluble sodium nitrate and insoluble silver chloride:silver nitrate + sodium chloride → sodium nitrate + silver chlorideAgNO3(aq) + NaCl(aq) → NaNO3(aq) +AgCl(s)The silver chloride appears as tiny particles suspended in the reaction mixture - it forms a precipitate. The precipitate can be filtered, washed with water on the filter paper, and then dried in an oven. Using precipitation reactions Precipitation reactions can be used to remove unwanted ions in solution. This is useful for treating drinking water and waste water.

Soluble Salts

Naming Salts

Crystallising Salt Solutions

Insoluble Salts