Acids, Alkalis and salts

Pure water is neutral and has a pH value of 7.

Acids are substances which produce hydrogen ions, H+(aq), when added to water.

When a substance is dissolved in water we use  the state symbol (aq) which stand for aqueous solution, to describe it being dissolved in water.

Bases react with acids to neutralise them.

Alkalis are bases that are dissolved in water to make the solution alkaline. Alkalis produces hydroxide ions, OH-(aq), in a solution. (They ahave a pH value greater than 7).

Indicators have different colours in acidic and alkaline solutions. Universal indicator (UI) and full range indicators have different colours at different pH values.

Acids will react with metals that are above hyrogen in the reactivity series.

However, the reactions of acids with very reactive metals, such as sodium and potassium, are too violent to be carried out safely.

When a metal reacts with a acid they produce a salt and hydrogen gas.

                              Acid      +     metal ---->   a salt    +    hydrogen

                       H2SO4(aq)   +   Zn(s)   ---> ZnSO4 (aq)  +   H2(g)

Metal oxide and metals hydroxide are bases. When an acid reacts with a bases neutralisation reaction take place and a salt and water are produced.Theses reactions can be used to make salts

                             Acid      +    base   ---->   a salt    +    Water 

                       2HCL(aq)   +   MgO(s)  ---> MgCl2 (aq)  +   H2O(l)

A metal, or a base that is insoluable in water, is added a little at a time to the acid, until all of the acid has reacted. leaving a solution of salt  dissolved in water.

The solid salt is formed when the water is avapourated from the solution so that it crystallises.

Crystallisation is a separation method that is used to seperate a solid that is dissolved in a liquid and has formed a solution.

Chlorides are made from hydrochloric acid, nitrates from nitric acid and sulfates from sulfuric acid.