Acids and Bases Acids and Bases
Acids Acidsgenerally have certain properties… • (a) Have a SOUR taste • (b) Change the colour of litmus indicator from BLUE to RED • (c) Conduct ELECTRICITY • (d) CORRODE most metals • (f) NUTRALISEbases. Acids are often found in foods
Bases Bases generally have certain properties… (a) Have a BITTER taste (b) Change the colour of litmus indicator from REDto BLUE (d) have a SOAPY feel (e) NUTRALISE acids. BASES are also called alkalis. Bases are generally used as cleaning agents
The pH Scale • The strength of acids and bases is measured on the “pH scale”. • Pure water has a pH value of 7, because it is neither acidic or basic, its Neutral. • Acids have a pH < 7 • Bases have a pH > 7 • The further away from 7 the pH gets, the stronger the acid or base. The strength of acids and bases is measured on the “pH scale”. Pure water has a pH value of 7, because it is neither acidic or basic, its Neutral. Acids have a pH < 7 Bases have a pH > 7 The further away from 7 the pH gets, the stronger the acid or base.
Indicators • An indicator is a chemical, or mixture of chemicals that react and change colour in the presence of an acid or a base. • Common indicators include: • Universal indicator • Methyl orange • Litmus • Phenolpthalein • Bromothymol blue
Universal Indicator Universal Indicator is a mixture of indicators and it allows us to not only determine whether the substance is an acid or base, but it gives some idea of the actual pH of the solution….
What have you learnt??? Questions • List the following as either an acid or base and put them in order from strongest to weakest: • pH 12, pH 5 pH 5.5, pH 1, pH 7, pH 9, pH 3 • Where is the most common place to find an acid and a base? • What is the pH of a substance that is neutral? • List 3 properties of an acid • List 3 properties of a base