9.03.3 Acids and Metals

Syllabus

(HT only) Students should be able to:

• explain in terms of gain or loss of electrons, that these are redox reactions

• identify which species are oxidised and which are reduced in given chemical equations.

Knowledge of reactions limited to those of Magnesium, Zinc & Iron with Hydrochloric & Sulphuric acids

Only reasonably reactive metals react with dilute acids - Gold and Copper do not.

They also make salts that are named in the same way, but instead of water they produce Hydrogen gas that would pop when lit.

So, generally Acid + Metal --> Salt + Hydrogen

Hydrochloric Acid + Sodium --> Sodium Chloride + Hydrogen

Sulphuric Acid + Calcium --> Calcium Sulphate + Hydrogen

Nitric Acid + Lithium --> Lithium Nitrate + Hydrogen

On the AQA syllabus we are only required to know about the reactions of Magnesium, Zinc and Iron with Hydrochloric and Sulphuric acid.

Learn the OILRIG Acronym - it will come in useful again and again.

You'll soon be learning all about electrons.

When one substance loses electrons another one must gain them.

So, when one substance is oxidised another must be reduced.

We sometimes call this Redox.

In the reaction between metals and acids, the metals lose and the Acids gain electrons - so both Oxidation and Reduction happen.

Hydrogen ions (H+) have a +1 charge.

Hydrogen atoms (in H2 molecules) have no charge.

The positive charge is cancelled out when each Hydrogen ion picks up a tiny negative particle called an electron - represented as e-.

2H+ + 2e- --> H2

The Hydrogen ions gain electrons so they are said to be reduced.

Where do the electrons come from?

They come from the metal atoms, which lose them to form positive metal ions and are Oxidised.

Mg --> Mg2+ + 2e-

Don't worry too much if Oxidation/Reduction doesn't mean much so far - we will return to it more than once.