Acids, Bases And Salt Preperations

Question 1

What does hydrochloric acid + a metal produce?

Answer 1

Metal chloride + hydrogen

Question 2

What does hydrochloric acid + a metal carbonate produce?

Answer 2

Metal chloride + water + carbon dioxide

Question 3

What does hydrochloric acid + a base (metal hydroxide) produce?

Answer 3

Metal chloride + water

Question 4

What does sulphuric acid + a metal carbonate produce?

Answer 4

Metal sulphate + water + CO2

Question 5

What does sulphuric acid + a metal make?

Answer 5

Metal sulphate + hydrogen

Question 6

What does sulphuric acid + a base (metal hydroxide) make?

Answer 6

Metal sulphate + water

Question 7

What does nitric acid + a metal produce?

Answer 7

Metal nitrate + hydrogen

Question 8

What does nitric acid + a metal carbonate produce?

Answer 8

Metal nitrate + water + carbon dioxide

Question 9

What substances are bases?

Answer 9

Metal oxides
Metal hydroxides
Ammonia

Question 10

Define acid, alkali and base.

Answer 10

A base in a proton acceptor (reacts with protons) Bases are compounds which can neutralise an acid and form a salt.

Alkalis are bases that are soluble (dissolve) in water.

All alkalis are bases, but not all bases are alkalis.

Question 11

State the general rules for predicting the solubility of ionic compounds in water.

Answer 11

• All nitrates, group one metals and ammonium compounds are soluble.
• Common chlorides are soluble, except for those of silver and lead(II).
• Common sulphates are soluble, except for those of barium, lead (II) and calcium.
• Common carbonates are insoluble, except for those of ammonium and group ones.
• Common hydroxides are insoluble except for those of group ones and calcium, which is slightly soluble.

Question 12

Describe an experiment to prepare a pure, dry sample of an insoluble salt, starting from two soluble reactants.
(Method one)

Answer 12

A (aq) + B (aq) —> C (s) + D (aq)

1. Mix A + B together
2. Filter
3. Wash the residue in the filter paper with pure/distilled water
4. Leave to dry (evaporate)

Question 13

Describe an experiment to prepare a pure, dry sample of a soluble salt starting from an insoluble reactant.
(Method two)

Answer 13

A (aq) (acid) + B (s) (metal/base/carbonate) —> C (aq) (salt) + (Water (l) or hydrogen (g) or carbon dioxide (g).

1. Add excess of the insoluble reactant (you will know when you’ve added excess because solid will remain visible). This makes sure that all the acid has been ‘used up’.
2. Filter to remove the excess insoluble reactant.
3. Heat the salt solution until it is saturated. When it is saturated, a glass, rod, when dipped into the solution and removed, will show crystals starting to form around it (because is less when solution is cooler). NB: never heat to dryness as an anhydrous powder will be obtained instead of crystals.
4. When it reaches this point, leave the solution to cool down and crystallise.

Question 14

Describe an experiment to prepare a pure, dry sample of a soluble salt, starting from an acid and alkali.
(Method three)

Answer 14

This method is called titration
A (aq) + B (aq) —> C (aq) + D (l)

1. A pipette is used to accurately measure a volume of an alkali, often 25 cm3. A pipette filler is used to draw solution into the pipette safely. The alkali is emptied into a conical flask.
2. A few drops of a suitable indicator are then added to the conical flask. This will show a change of colour when the acid and alkali have neutralised one another and the titration is complete.
3. The acid is placed in a burette and the starting volume of acid is read against the scale marked on the burette.
4. The acid from the burette is added to the conical flask, and the flask is swirled to mix its contents. When the acid in the burette has almost run in, it is added one drop at a time. Eventually, a colour change shows that the correct amount has been added to react completely with the alkali in the conical flask.
5. The volume of acid added from the burette is noted. The titration results can then be used to calculate the concentration of the acid or alkali (if the concentration of the other is known).

Universal indicator is unsuitable for titrations because it has a range of colours. Phenolphthalein is often used instead. It changes from pink in alkali to colourless in acid.

Question 15

What is an ionic equation?

Answer 15

An equation in which all the spectator ions (ions which didn’t change state in the reaction: are the same before and after) are crossed out.

Question 16

Describe an experiment to prepare a sample of pure, hydrated copper (II) sulphate crystals starting from copper (II) oxide.

Answer 16

Copper (ll) oxide + sulphuric acid —> copper sulphate + water
H2SO4 (aq) + CuO (s) —> CuSO4 (aq) + H2O (l)

Method 2

1. Put sulphuric acid into a beaker
2. Add copper (ll) oxide to acid until there is an excess
3. Mix with a glass rod
4. Filter to separate the copper (ll) oxide from the salt solution
5. Heat the solution until it is saturated
6. Leave to cool down and crystallise

Question 17

Describe an experiment to prepare a sample of pure, dry lead (II) sulphate starting from lead (II) nitrate.

Answer 17

Lead (ll) nitrate solution + sodium sulphate solution —> lead (ll) sulphate precipitate + sodium nitrate solution.
Pb(NO3)2 (aq) + Na2SO4 (aq) —> PbSO4 (s) + 2NaNO3 (aq)

Method 1

1. Mix lead (ll) nitrate and sodium sulphate together
2. Filter the mixture so that a residue is left in the filter paper
3. Wash the residue with pure/distilled water
4. Leave the residue to dry