pH scale and neutralisation

• the pH scale is a measure of acidity or alkalinity of a solution.
• the pH scale is from 0 to 14.
• pH can be measured using:

  • universal indicator
  • pH probe
• a solution with a pH of 7 is neutral.
• aqueous solutions of acids have a pH of less than 7.
• aqueous solutions of alkalis have a pH of more than 7.
• in a neutralisation reaction between an acid and alkali, hydrogen ions react with hydroxide ions to produce water.
• the chemical equation for neutralisation is:

  H+ + OH- react to form H2O
• an indicator is a group of chemical dyes that change colour depending on pH.
• universal indicator gradually changes colour as it it is a wide range indicator.
• a pH probe electrically measures the pH, which shows a numerical reading on a metre.
• the use of a pH probe is more accurate and precise as it removes the need of human judgement.
• an alkali is a base that dissolves in water to form a solution with a pH greater than 7.
• common acids:

  • hydrochloric - HCl
  • sulfuric - H2SO4
  • nitric - HNO3
• common bases:

  • sodium hydroxide - NaOH
  • calcium carbonate - CaCO3
• neutralisation reactions:

  1. metal oxides + acids react to form salt + water
  2. metal hydroxide + acid react to form salt + water
  3. metal carbonate + acid react to form salt + water + carbon dioxide