# Titration curves (pH)

Titration curves can be described as what happens before, after and during the equivalence point.

1. ### Titration curves for strong acid v strong base

###### Running acid into the alkali
• The pH drops very little until it reaches the equivalence point, where it drops steeply
• Then, it continues to fall by small amounts

###### Running alkali into the acid
• This is very similar to the previous curve except the pH starts off low and increases as you add more sodium hydroxide solution.

1. ### Titration curves for strong acid v weak base

###### Running acid into the alkali
• The initial gradient is steeper than before, since a strong acid is being added to a weak base
• However, after some acid is added, it slows and looks similar to before
• This is because it forms a buffer solution
• Note that, whilst the steep point is still steep, it is smaller than before
• Hence, the pH range that you need to use is smaller

###### Running alkali into the acid
• The shape is still the same as #1, due to an excess of HCl
• After the equivalence point, there is no large change in pH due to a buffer solution being formed
• Note that the equivalence point occurs when the solution is acidic

1. ### Titration curves for weak acid v strong base

###### Running acid into the alkali
• Before, the curve is the same as #1, as you have an excess of NaOH
• Again, the equivalence point occurs during a smaller pH range
• Past the MEP, a buffer solution is created, so pH change is minimal
• Note that the MEP occurs when the solution is basic

###### Running alkali into the acid
• The start of the graph shows a relatively steep curve, as you are adding a strong base to a weak acid
• This however slows as a buffer is established
• After, the curve is the same as #1

1. ### Titration curves for weak acid v weak base

###### Running alkali into the acid

• It so happens that these two are both about equally weak – in that case, the equivalence point is approximately pH 7.
• THIS IS NEVER DONE IN PRACTISE, as the endpoint would likely miss the MEP, since the pH range is so small.
###### Running acid into the alkali
• This is just a combination of graphs.
• Up to equivalence point, it is just like #2
• Equivalence point has a very small pH range
• Lack of a steep section means it is difficult to measure exactly when MEP has been reached