Reactions of Acids

Neutralisation A neutral substance has a ph =7. It

contains equal numbers of H+ and OH-

Neutralisation is when we reduce the number of H+ ions in an acid or reduce the number of OH- ions in an alkali – so that they become neutral.

Neutralising Acids

If we add a BASE to and acid we can neutralise it.

There are 4 types of BASE: Metals, Metal oxides, Metal hydroxides

(soluble metal hydroxides are – alkali’s) and Metal Carbonates.

A new substance called a “salt” is always produced.

Naming Salts

The first part of the name comes from the base – it will be a metal name.

The second part comes from the acid.

Salts usually end in “ ide” or “ ate

Acid Base Salt

Hydrochloric Sodium

hydroxide

Sodium

chloride

Sulphuric acid Calcium

Hydroxide

Calcium

sulphate

Bases

Metals

Metal + Acid —>Salt + Hydrogen

Example Magnesium + Hydrochloric Acid —>

Magnesium chloride ( salt) + Hydrogen

Metal oxides

Metal oxide + Acid —>

Salt + Water

Example

Magnesium oxide + Carbonic Acid —>

Magnesium carbonate + Water

(salt)

Metal hydroxide ( alkali)

Metal hydroxide + Acid —>

Salt + Water

Example

Calcium hydroxide + Nitric Acid —>

Calcium nitrate + Water

Metal carbonate

Metal carbonate + Acid —>

Salt + Water + Carbon dioxide

Example

Sodium carbonate + Sulphuric Acid —>

Sodium sulphate + Water + Carbon dioxide

Ionic Equations

Step 1. Write down normal balanced equation,

remember to use valency to work out formula of compounds.

Step 2 Put in the charges of the ions in the ionic

compounds in the equations – remember – covalent compounds e.g. Water don’t have ions!

Example of Ionic Equation

Calcium oxide + Hydrochloric Acid —>Calcium chloride + Water

Step 1

Ca O + H Cl —> Ca Cl2+ H2OStep 2

Ca 2+ O 2- + H+ Cl- —> Ca 2+ (Cl-)2 +

H2O(l)

Spectator Ions

These are ions which do not change

during the reaction – they are exactly the same on the left and fight side of the arrow!

Example

H+ CL- + Na+ OH- —> Na+ Cl- + H2O

The Na+ and Cl- ions have not changed – they are the spectator ions in this reaction.

Making Insoluble Salts

We can make an insoluble salt when we mix certain salt solutions.

This is called Precipitation! Use p5 in Data booklet to check solubility of

compounds! Example Barium nitrate(s) + Sodium sulphate(s) They swap partners- Barium sulphate(i) and

Sodium nitrate(s) are formed. Barium sulphate is insoluble – it is a precipitate!

Volumetric Titrations

This is when we work out the volume or concentration of an acid or alkali required for a neutralisation reaction.

C1 V1 = C2 V2

C1 = Concentration of Acid V1 = Volume of Acid C1 = Concentration of Alkali V1 = Volume of Alkali

Examples!

Calculate the concentration of acid required id 20 cm3 neutralises 20 cm3 of 2mol/l alkali.

C1 V1 = C2 V2 We are wanting to calculate C1 C1 = C2 V2 / V1 C1 = 2 x 0.02 / 0.02

= 2 mol/l

Example 2

What volume of alkali, with a concentration of 3 mol/l, is required to neutralise 50 cm3 of 2 mol/l acid?

C1 V1 = C2 V2 V2 = C1 V1 / C2 = 2 x 0.05/ 3

= 0.03 Litres