Topic 2f Acids, bases and salt preparations

Alkalies are part of a wider group of comounds

That can neutralise an acid called bases

Base

A substance that can react with an acid and neutralise it

Alkali

A base that is soluble in water

How does a base neutralise an acid

It accepts the proton - the hydrogen ion - that is donated by the acid

What is another word for bases

Proton acceptors

What is always formed when a metal reacts with an acid

A metal salt and hydrogen

Metal + acid -->

Metal salt + hydrogen

A metal reacting with an acid

Is not always a neutralisation reaction, as the products are not necessarily neutral

The metal salt is always

An ionic compaound, with the first part of the name being the metal ion and the second part being the negative ion

Potassium + hydrochloric acid -->

Potassium chloride + hydrogen

2K + 2HCl -->

2KCl + H2

Observations when magnesium reacts with hydrochloric acid

Fizzing and rise in temperature

Observations when calcium reacts with hydrochloric acid

Very vigorous reaction, lots of fizzing

Metal carbonates are

Bases that are mostly insoluble in water

Metal carbonate + acid -->

Metal salt + water + carbon dioxide

Metal carbonates react with and neutralise acids to form

A metal salt, water and carbon dioxide

Calcium Carbonate + sulphuric acid -->

Calcium sulfate + water + carbon dioxide

Metal hydroxide + acid -->

Metal salt + water

Sodium hydroxide + nitric acid -->

Sodium nitrate + water

Metal oxides are bases, but

As they are not soluble or a source of hydroxide ions they are not alkalis

All alkalis produce

OH- ions in an aqueous solution

Metal oxide + acid -->

Metal salt + water

Copper oxide + sulphuric acid -->

Copper sulphate + water

Metal oxides react with acids to form

Metal salt and water

Ammonia + acid -->

Ammonium salt

Ammonia + hydrochloric acid -->

Ammonium chloride

Why do we want pure samples of metal salts

Because they can be useful, but they must be pure

What is the first step to prepare salts (make a pure sample)

Add an excess of base to the acid. This is when you can see unreacted base in the liquid

What do you do with the saturated base/acid mixture to prepare a pure sample of metal salts

Put it through the filter paper to remove the excess base. The solution will be the solution of the metal salt.

What do you do with the metal salt solution to prepare a pure sample of metal salts

Remove the water from the solution by evaporation

What salt compounds are soluble

Common sodium, potassium and ammonium compounds

All... are soluble

Nitrates

Common Chlorides

Are soluble, except those of silver and lead(II)

Common sulphates

Are soluble, except for those of barium, calcium ad lead

Common carbonates,

Are insoluble, except for those of sodium, potassium and ammonium

Common hydroxides

Are insoluble except for those of sodium, potassium and calcium

Calcium hydroxide is

Slightly soluble