C4 Chemical Calculations

Question 1

What is a substance called that has a pH under 7?

Answer 1

An Acid

Question 2

If a substance is over 7 in pH the substance is a?

Answer 2

An alkali

Question 3

How can you measure the pH of a solution

Answer 3

Use an indicator (a dye that changes it’s colour depending on the pH of the solution)
Or
A pH probe attached to a pH meter that can be used to measure pH electronically

Question 4

What is a base?

Answer 4

A substance that has a pH greater than 7

Question 5

What happens when you add an acid to a base?

Answer 5

Acid + base -> salt + water

Question 6

What are titrations for?

Answer 6

Titrations allow you to find out exactly how much acid is needed to neutralise a quantity of an alkali

Question 7

Titration method…

Answer 7

• using a pipette and pipette filler add a set volume of the alkali to a conical flask. Add two or three drops of indicator too
• use a funnel to fill a burette with some acid of known concentration (make sure you do this below eye level - you don’t want to measure inaccurately or spill a bit on YOUR FACE) record the initial volume
• using a burette add acid to the alkali a bit at a time (give the flask a regular swirl) - go especially slow when you think the end point (colour change) is about to be reached
• the indicator permanently changes colour when all alkali have been neutralised (permanent colour change)
• record the final volume of the acid in the burette and use it to calculate the volume of acid needed to neutralise the alkali