Chemistry: Acids, Bases and Salts

Question 1

Describe neutrality and relative acidity and
alkalinity in terms of pH (whole numbers
only) measured using full-range indicator and
litmus.

Answer 1

Neutral - pH of 7.
Acidic - pH < 7
Alkaline - pH > 7
Universal indicator - Colour determines pH. Red to Blue, neutral = green.
Blue litmus paper turns red under acidic conditions, Red goes to blue under alkaline conditions. Purple litmus paper - neutral

Question 2

Describe the characteristic reactions of acids
with metals, bases (including alkalis) and
carbonates.

Answer 2

Acids are neutralised by bases and carbonates to form a salt and water (+ CO2), acid reacts with metal to form a salt and release hydrogen gas.

Question 3

Describe and explain the importance of
controlling acidity in the environment (air,
water and soil).

Answer 3

Soil - Plants prefer a neutral pH to grow.
Air - Can cause acid rain, erodes buildings.
Water - Harms the environment.

Question 4

Describe the preparation, separation and
purification of salts using techniques
selected from section C2.1 and the reactions
specified in section C8.1.

Answer 4

Filtration, evaporation, leave to cool.

Question 5

Suggest a method of making a given
salt from suitable starting material, given
appropriate information.

Answer 5

Depends.

Question 6

Identify:
aqueous cations:
•	 ammonium, copper(II), iron(II), iron(III)
and zinc by means of aqueous sodium
hydroxide and aqueous ammonia as
appropriate (formulae of complex ions
are not required)

Answer 6

2Cu + 2NaOH –> 2NaCuO + H2
NB: Metal + Base –> Salt + Hydrogen Gas
Fe(3+) + NaOH –> NaFeO + H2
Fe(3+) + NaOH –> Na(Fe2O3) +

Question 7

Identify:
anions:
•	 carbonate by means of dilute acid and
then limewater
•	 chloride by means of aqueous silver
nitrate under acidic conditions
•	 nitrate by reduction with aluminium
•	 sulfate by means of aqueous barium ions
under acidic conditions

Answer 7

Carbonate: Reaction of carbonates with acids produces a salt, water and carbon dioxide gas, which can be identified by bubbling the gas through limewater, positive result turns limewater milky white,
Chloride: Ag+(aq) + Cl-(aq) → AgCl(s)
To test for halide ions:
add a few drops of dilute nitric acid to the sample
add a few drop of dilute silver nitrate solution
Observe and record the colour of any precipitate that forms. Chloride = white
Nitrate: