Titrations

Question 1

What happens in a titration?

Answer 1

An acid and an alkali neutralise.

Acid + alkali —> salt + water

Question 2

What happens during a neutralisation reaction?

Answer 2

• 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

Question 3

What indicators can be used in a titration?

Answer 3

• Phenolphthalein: pink to colourless
• Litmus: blue to red
• Screened methyl orange: green to pink

Question 4

Why is universal indicator (UI) not used?

Answer 4

It gives a gradual colour change and is harder to see when the end point is.

Question 5

What are titrations used for?

Answer 5

To find the concentration of an alkali from a known concentration of acid or vice versa.

Question 6

How do we use titrations to find the concentration?

Answer 6

• 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

Question 7

A 23.8cm^3 solution of 0.11mol/dm^3 of HCl reacts with 25.0cm^3 of NaOH. Find the concentration of NaOH.

Answer 7

• 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