C5 - pH Curves and Titrations

Question 1

General word equation for neutralisation reactions? When do acids and alkalis form in terms of pH?

Answer 1

Acid + alkali -> salt + water

Acids form solutions with a pH less than 7, and alkalis
form solutions with a pH more than 7.

Question 2

Describe the pH curve for adding an acid to an alkali

Answer 2

Negative , sudden drop in the middle

Question 3

Describe the pH curve for adding an alkali to an acid

Answer 3

Positive , sudden increase in the middle

Question 4

What do the sudden changes in pH curves show?

Answer 4

The end point of the reaction is when the acid and alkali exactly neutralise each other. There is a sudden change in pH at the end point.

Question 5

Describe how examples of single indicators work

Answer 5

• Phenolphthalein is pink in alkaline solutions and colourless in acidic solutions.
• Litmus is blue in alkaline solutions and red in acidic solutions.

Question 6

What is universal indicator? How does it work?

Answer 6

It is a mixed indicator. It contains several different indicators. Each one changes colour over a different range of pH values. This is why universal indicator gives a continuous colour change. It lets you find the approximate pH of a solution, but it is not suitable if you want to know the precise end point in a titration.

Question 7

What are titrations? What indicator is used and why?

Answer 7

A method to find the concentration of an acid or alkali using a neutralisation reaction. A single indicator such as phenolphthalein is used, as it gives a sudden colour change between pink and colourless at the end point.

Question 8

What is a titre?

Answer 8

The difference between the start and end readings on the burette gives the titre. This is the volume of acid needed to exactly neutralise the alkali.

Question 9

How do you work out titration calculations?

Answer 9

Watch videos and practise questions. Table thing