Chemistry C2.5

C2 5.1

Water is neutral and has a pH of 7. Acids are substances that produce hydrogen ions when added to water (H+ ions). When we dissolve a susbance in water we make an aqueous solution (aq).

Hydrogen ions make solutions acidic, because they have a pH of less than 7.

Bases can react with acids to neutralise them. Alkalis are bases that dissolve in water to make hydroxide ions (OH-).

The pH scale goes from 0 to 14. A number below 7 is acidic and a number above 7 is alkali. Universal indicator is used to see what pH an aqueous solution has from its colour.

C2 5.2

Acids will react with any metal above hydrogen on the periodic table. But with very reactive metals, like sodium and potassium, this can become dangerous. When metals react with acids, they produce a salt and hydrogen.

When an acid reacts with a base (can be metal oxides or metal hydroxides too), a neutralisation reaction occurs and salt and water are bi-products.

Both of these reactions are useful to make salts.

A metal or a base that is insoluble is added at little amounts at a time until it has all reacted. The mixture is then filtered to remove the solid.

To get the salt from the water, you evaporate the water so that the salt is left behind.

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

C2 5.3

To make soluble salts you can react an acid with an alkali. This creates water with the salt. The neutralisation between the acid and the alkali can be shown by the following equation: H+(aq) + OH-(aq) -> H2O(l). However, the reaction doesn't make the aqueous look any different; we must use a pH meter to determine when the reaction is complete.

To make an insoluble salt, you mix two aqueous solutions and form…