Neutralisation Worksheet

Acids and alkalis react together to form new products in a neutralisation reaction.

If exactly the right amount of alkali is added to an acid, the resulting solution will have a pH of seven because the acid and alkali will 'cancel' each other out.

Indicator scale for pH

This means that the pH of the acid increases towards seven during neutralisation, but the pH of the alkali decreases towards seven.

Neutralisation reactions are performed every day. For example in the treatment of acid indigestion, or a farmer adding quicklime (an alkali) to his fields to neutralise acidic soil.

Acids and alkalis can also be used to treat insect stings:

Calamine lotion (an alkali) can be used to treat bee stings which are acidic.

Vinegar (an acid) can be used to treat wasp stings which are alkaline.

...Just don’t get the two mixed up or it may make the sting more painful – ouch!

Using the table below, decide which of the following substances would neutralise an alkali.

Tick all you agree with.

vinegar

lemon juice

chalk

bicarbonate of soda

quicklime

fizzy drink

calamine lotion

Type this sentence out again in the answer box below, filling out the gap with the correct word. Don't forget the full stop!

When an acid is neutralised its pH _________ towards pH 7.

Type this sentence out again in the answer box below, filling out the gap with the correct word. Don't forget the full stop!

When an alkali is neutralised its pH _________ towards pH 7.

Which of the following would neutralise a bee sting?

Vinegar

Lemon juice

Baking soda

Which of the following would neutralise a wasp sting?

Vinegar

Milk of magnesia

Baking soda

Use the previous information to match the substances on the right with those that they would neutralise on the left.

Column A	Column B
Vinegar	Hydrochloric acid
Sodium hydroxide	Bicarbonate of soda

ANSWERS

ANSWERS

Question 2

Tick the substances below that would neutralise an acid:

CORRECT ANSWER

chalk
bicarbonate of soda
quicklime
calamine lotion

EDDIE SAYS

All of the ticked substances are alkaline and would therefore neutralise an acid. Vinegar, lemon juice and most fizzy drinks are themselves acids.

ANSWERS

Question 3

Using the table below, decide which of the following substances would neutralise an alkali.

Tick all you agree with.

CORRECT ANSWER

vinegar
lemon juice
fizzy drink

EDDIE SAYS

These substances are acidic, so they would neutralise an alkali. As you've already noted, the rest are alkalis anyway.

ANSWERS

Question 4

Type this sentence out again in the answer box below, filling out the gap with the correct word. Don't forget the full stop!

When an acid is neutralised its pH _________ towards pH 7.

CORRECT ANSWER

When an acid is neutralised its pH increases towards pH 7.
When an acid is neutralised its pH rises towards pH 7.

EDDIE SAYS

During neutralisation the pH of an acid increases towards 7 and the pH of an alkali decreases towards 7. Think about it: you start with an acid (pH is below 7). To get it to neutral (pH7) the pH of the mixture is going to have to increase, isn't it? For example, starting pH = 3. End pH = 7. It's risen and it'll take an alkali of, say, pH 11 to do that. OK?

ANSWERS

Question 5

Type this sentence out again in the answer box below, filling out the gap with the correct word. Don't forget the full stop!

When an alkali is neutralised its pH _________ towards pH 7.

CORRECT ANSWER

When an alkali is neutralised its pH decreases towards pH 7.
When an alkali is neutralised its pH falls towards pH 7.

EDDIE SAYS

Neutralisation of an acid or alkali moves the pH towards 7.

Alkalis have a pH greater than 7 so the pH will decrease during neutralisation and acids have a pH of less than 7 so their pH will increase during neutralisation. So, say the alkali starts at pH9. To get it to pH7 the pH value must .... decrease! That'll need an acid, e.g. pH=2.

ANSWERS

Question 6

Which of the following would neutralise a bee sting?

CORRECT ANSWER

Baking soda

EDDIE SAYS

Bee stings are acidic so an alkali such as baking soda will neutralise the sting. There's a little rhyme to help you remember this: "Vinegar - Vasp, Bicarb - Bee". In other words, wasp stings are treated with vinegar (an acid) and bee stings with bicarb(onate of soda) - an alkali. Worth remembering, that!

ANSWERS

Question 7

Which of the following would neutralise a wasp sting?

CORRECT ANSWER

Vinegar

EDDIE SAYS

Wasp stings are alkaline so an acid such as vinegar would neutralise the sting. Remember that little rhyme: "Vinegar - Vasp, Bicarb - Bee". In other words, wasp stings are treated with vinegar (an acid) and bee stings with bicarb(onate of soda) - an alkali.

ANSWERS

Question 8

Use the previous information to match the substances on the right with those that they would neutralise on the left.

CORRECT ANSWER

Column A	Column B
Vinegar	Bicarbonate of soda
Sodium hydroxide	Hydrochloric acid

EDDIE SAYS

Remember, vinegar is a weak acid, so needs a weak alkali (bicarb of soda) to neutralise it. Similarly, the strong alkali sodium hydroxide (it's really nasty stuff!) can be neutralised by the strong acid, hydrochloric acid. Mind you, this last reaction will get fairly warm as it goes on - one to be careful with!