Acids and bases
An acid releases ions in water; a base releases ions (or accepts ions, in the broader definition). The pH scale runs from 0 (strongly acidic) through 7 (neutral) to 14 (strongly alkaline).
Neutralization
When an acid reacts with a base, the and ions combine to form water, and the remaining ions form a salt: acid + base salt + water.
Example 1: Write the equation for the neutralization of hydrochloric acid with sodium hydroxide.
-- the salt formed is sodium chloride.
Preparing salts
Soluble salts are commonly prepared by titration (reacting a measured acid with a base using an indicator to find the exact neutralization point) or by reacting an acid with an excess of a metal, insoluble base, or carbonate and then filtering off the unreacted excess. Insoluble salts are prepared by precipitation -- mixing two soluble solutions so their ions combine to form an insoluble solid that can be filtered out.
Example 2: Describe how to prepare solid copper(II) sulfate crystals from copper(II) oxide and dilute sulfuric acid.
Add excess copper(II) oxide to warm dilute sulfuric acid until no more dissolves (this ensures all the acid has reacted). Filter off the unreacted excess oxide, then heat the blue filtrate gently to evaporate some water and leave it to cool -- copper(II) sulfate crystals form as the solution cools.
Indicators
Litmus turns red in acid and blue in alkali. Phenolphthalein is colourless in acid and pink in alkali. Universal indicator gives a range of colours corresponding to the approximate pH value, making it useful for estimating strength as well as identifying acid or base.