Titrations and pH curves Flashcards
What does a titration show you?
Exactly how much alkali is needed to neutralise a quantity of acid
What is the first stage of doing a titration?
- Measure out acid of a known concentration using a pipette and add into a flask with an appropriate indicator
What is an indicator?
They change colour at a certain pH
What is the second stage of doing a titration?
- Do a rough titration to get an approximate idea of where the solution changes colour which is the end of point
What is the end point?
The point at which all of the acid is just neutralised
What is the third stage of doing a titration?
Repeat step one and do an accurate titration
Run the alkali in to within 2cm3 of the end point then add drop by drop
What has happened if you don’t notice exactly when the solution changes colour?
you have overshot and the results wont be accurate
How many times should you repeat and why?
A few times
until you have 3 concordant results within 0.1cm3 of each other then work out a mean
Describe the curve when a strong base is added to a strong acid?
The graph will start at around pH 1 and end at around pH 13
Describe the curve when a weak base is added to a strong acid?
The graph will start at around pH 1 and end at around pH 9
Describe the curve when a strong base is added to a weak acid?
The graph will start at around pH 5 and finish at around pH13
Describe the curve when a weak base is added to a weak acid?
The graph will start at around pH 5 and finish at about pH 9
What is the part of the graph that is almost vertical equivalent to?
The end point
What type of titration are you best using a pH meter for and why?
Weak acid/weak base
The colour will change very gradually and it is very tricky to actually see an end point
How do you decide which pH indicator to use?
Look at the pH range it covers and it should cover the whole vertical range
