1
Q
What happens in a titration?
A
An acid and an alkali neutralise.
Acid + alkali —> salt + water
2
Q
What happens during a neutralisation reaction?
A
- Only alkali is present at the beginning
- As an acid is added it starts the neutralise the alkali and the pH slowly drops
- The point where all the acid reacts with the alkali is called the end point and the pH changes very suddenly
3
Q
What indicators can be used in a titration?
A
- Phenolphthalein: pink to colourless
- Litmus: blue to red
- Screened methyl orange: green to pink
4
Q
Why is universal indicator (UI) not used?
A
It gives a gradual colour change and is harder to see when the end point is.
5
Q
What are titrations used for?
A
To find the concentration of an alkali from a known concentration of acid or vice versa.
6
Q
How do we use titrations to find the concentration?
A
- Find how many moles of acid were used
- Equate the known number of moles to the alkali number of moles
- Acid moles = alkali concentration X alkali volume
- Alkali concentration = acid moles/alkali volume
7
Q
A 23.8cm^3 solution of 0.11mol/dm^3 of HCl reacts with 25.0cm^3 of NaOH. Find the concentration of NaOH.
A
- Convert 23.8cm^3 into dm^3, 23.8/1000 = 0.0238dm^3
- Moles of acid = 0.11 X 0.0238 = 0.00262
- Convert 25cm^3 into dm^3, 25/1000 = 0.025
- 0.00262 = 0.025 X alkali concentration
- Alkali concentration = 0.00262/0.025 = 0.105mol/dm^3
