Lesson 20 - Chemical Reactions - Indicators to show Acids and Bases: 9S2 Science

Learning Intentions

To investigate the use of indicators to determine acids and bases.

Acids and Bases

An acid is a substance that produces hydrogen ions ($H^+$) when dissolved in water. Acids usually have a $pH$ less than 7 ($pH < 7$). Examples include hydrochloric acid ($HCl$), sulfuric acid ($H_2SO_4$), and nitric acid ($HNO_3$).

A base is a substance that neutralises an acid. Bases produce hydroxide ions ($OH^-$) when dissolved in water and usually have a $pH$ greater than 7 ($pH > 7$). Examples include sodium hydroxide ($NaOH$), potassium hydroxide ($KOH$), and calcium hydroxide ($Ca(OH)_2$).

Indicators

An indicator is a substance that gives a visible sign, usually a color change, to show the presence of a chemical species or the endpoint of a reaction. Indicators are most commonly used to test $pH$ levels in acid-base titrations.