What is the end-point of a titration?

when the indicator just changes colour. At that point the acid has exactly neutralised the alkali.

Which piece of apparatus is the acid added from?

a burette. A burette lets you add any volume and read it accurately.

Why is the flask swirled during a titration?

to mix the solutions. Otherwise the colour change is patchy and the end-point is missed.

Why is universal indicator not used in titrations?

Its colour changes gradually, so there is no sharp end-point. A single, sudden colour change is needed.

After a rough titration, how should the acid be added near the end-point?

a drop at a time. One drop can be enough to change the colour.

Titrations · Cambridge IGCSE Co-ordinated Sciences (9

In plain words

A titration finds exactly how much acid cancels out an alkali. You drip acid from a burette into the alkali, with an indicator in it, and stop the instant the colour changes. That instant is called the end-point.

Three things to know

Measure out the alkali with a pipette into a conical flask. Add a few drops of indicator. Add acid from the burette, swirling, until the indicator just changes colour.
Methyl orange is yellow in alkali and red in acid. Thymolphthalein is blue in alkali and colourless in acid; phenolphthalein is pink in alkali and colourless in acid.
Do a rough run first, then repeat adding the acid drop by drop near the end, until two results agree closely.

Worked example

A burette reads 1.20 cm³ at the start of a titration and 24.70 cm³ at the end. How much acid was added?

Volume added = final reading − start reading.
= 24.70 − 1.20.
= 23.50 cm³.

Tips and tricks

Read a burette from the bottom of the curve (the meniscus), with your eye level with it.
Stand the flask on a white tile so the colour change is easy to see, and swirl after every addition.

5 questions, about 2 minutes.

It lands in your notebook with its questions as flashcards.

Titrations: 5 questions and answers

These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.

What is the end-point of a titration?
- when the burette is empty
- when the indicator just changes colour (the answer)
- when the flask is full
- when the solution boils
At that point the acid has exactly neutralised the alkali.
Which piece of apparatus is the acid added from?
- a pipette
- a burette (the answer)
- a measuring cylinder
- a beaker
A burette lets you add any volume and read it accurately.
Why is the flask swirled during a titration?
- to cool it
- to mix the solutions (the answer)
- to dissolve the glass
- to remove bubbles
Otherwise the colour change is patchy and the end-point is missed.
Why is universal indicator not used in titrations?
- It is too expensive.
- Its colour changes gradually, so there is no sharp end-point. (the answer)
- It is not affected by acids.
- It is a solid.
A single, sudden colour change is needed.
After a rough titration, how should the acid be added near the end-point?
- all at once
- a drop at a time (the answer)
- from a beaker
- without swirling
One drop can be enough to change the colour.

5 questions

Tap an answer and you’ll see straight away whether it’s right, and why.

Worksheet

3 questions, 7 marks. Write your answers on paper, then check them.

Titrations

Cambridge IGCSE Co-ordinated Sciences (9–1) 0973 · 7 marks · papermunch.org

Name ______________________________ Date ______________

Describe how to carry out a titration to find the volume of hydrochloric acid needed to neutralise 25.0 cm³ of sodium hydroxide solution.[4]
Show answerHide answer
Use a pipette to put 25.0 cm³ of the alkali in a conical flask and add a few drops of indicator. Fill a burette with acid and note the reading. Add acid, swirling, until the indicator just changes colour. Note the reading and subtract. Repeat until results agree.
I got this one
Explain why a titration is repeated.[2]
Show answerHide answer
To check the result is reliable, and to get results that agree closely so that a mean can be taken.
I got this one
Explain why the flask is placed on a white tile.[1]
Show answerHide answer
So that the colour change of the indicator can be seen clearly.
I got this one

Answers: Titrations

1. Use a pipette to put 25.0 cm³ of the alkali in a conical flask and add a few drops of indicator. Fill a burette with acid and note the reading. Add acid, swirling, until the indicator just changes colour. Note the reading and subtract. Repeat until results agree.
2. To check the result is reliable, and to get results that agree closely so that a mean can be taken.
3. So that the colour change of the indicator can be seen clearly.