Neutralisation and pH scale

strong acids

ionise COMPLETELY in water

all the acid particles dissociate to release lots of H⁺ ions

concentrated acids

a higher ratio of acid compared to water

weak acids

• do not fully ionise in solution

• only a small proportion of acid particles dissociate to release H⁺ ions

• this is REVERSIBLE

• it sets up an EQUILIBRIUM between dissociated and dissociated acid

• the equilibrium lies well to the left since only a few acid particles dissociate to release H⁺ ions

dilute acids

a small ratio of acid compared to water

pH

measure of the concentration of H⁺ ions

How does pH increase/decrease as concentration of H⁺ ions increase/decrease?

for every increase/decrease of 1 pH, the concentration of H⁺ ions decreases/increases by a factor of 10

Factor H⁺ ion concentration changes by = 10^{difference in pH}

Neutralisation

• acids release H⁺ ions when dissolved in water

• alkalis release OH^- ions when dissolved in water

• these form H₂O

neutralisation ionic equation

H⁺ + OH^- —> H₂O

Describe and explain the trends in this graph

• pH falls gradually at first as acid added

• then more rapidly as alkali is completely neutralised

• At pH 7, this is the equivalence point- how much acid neutralises alkali

• then pH falls slowly again as excess acid is added

Describe and explain the trends in this graph

• pH rises gradually at first as alkali added

• then more rapidly as acid is completely neutralised

• At pH 7, this is the equivalence point- how much alkali neutralises acid

• then pH increases slowly again as excess alkali is added