Neutralisation

L.O: TO understand neutralisation reactions in terms of ions

20/04/23

Universal Indicator and the pH scale

Strong acid Strong alkaliNeutral

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Universal Indicator is a mixture of liquids that will produce a range of colours to show how strong the acid or alkali is:

Stomach acid

Lemon juice

Water Soap Oven cleaner

Baking powder

An acid contains hydrogen ions, H+

An alkali contains hydroxide ions, OH-

Making water into acids and alkalis Making water into acids and alkalis

Some compounds react with water to create acidic or alkaline solutions

Alkalis, in aqueous solutions produce OH- (aq) hydroxide ions

Acids, in aqueous solutions contain H+ (aq) hydrogen ions

In the HCl gas fountain why does the water turn red with Universal indicator?

The same thing can be done with ammonium hydroxide. What colour would the universal indicator turn?

In neutralisation these ions react what do they form when put together?

OH-(aq)

+ H+(aq)

20/04/23

Neutralisation reactionsWhen acids and alkalis react together they will NEUTRALISE each other:

OHNa

Sodium hydroxide

ClH

Hydrochloric acid

The sodium “replaces” the hydrogen from HCl

ClNa

Sodium chloride

H2O

Water

General equation: H+(aq) + OH-

(aq) H2O(l)

Match the reactants to their products

hydrochloric acid + sodium hydroxide calcium nitrate + water

hydrochloric acid + potassium hydroxide calcium chloride + water

hydrochloric acid + calcium hydroxide sodium sulphate + water

nitric acid + sodium hydroxide calcium sulphate + water

nitric acid + potassium hydroxide sodium nitrate + water

nitric acid + calcium hydroxide sodium chloride + water

sulphuric acid + sodium hydroxide potassium nitrate + water

sulphuric acid + potassium hydroxide potassium chloride + water

sulphuric acid + calcium hydroxide potassium sulphate + water

20/04/23

Making saltsWhenever an acid and alkali neutralise each other we are left with a salt, like a chloride or a sulphate. Complete the following table:

Hydrochloric acid

Sulphuric acid

Nitric acid

Sodium hydroxide

Sodium chloride + water

Potassium hydroxide

Potassium sulphate + water

Calcium hydroxide

Calcium nitrate + water

Your task is to find out what volume of acid is needed to neutralise your concentration of alkali

Set up your burette as your teacher has shown you

Add 10ml of your alkali using a pipette to a conical flask and add a few drops of universal indicator

Fill up your burette with your alkali

Slowly add the alkali swirling the conical flask as you go

Stop when your solution becomes neutral

Record the volume of acid needed

Class results

Alkali concentration (mol / dm3)

Volume of acid to netralise (ml)

Conclusion

What is the pattern / trend

in terms of ions why does a higher concentration need less acid to neutralise (4 marks)

How accurate do you think the burettes are?

Are our results reproducible?