Chemistry: Acids, Bases and Salts
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Describe neutrality and relative acidity and alkalinity in terms of pH (whole numbers only) measured using full-range indicator and litmus.
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
Describe the characteristic reactions of acids with metals, bases (including alkalis) and carbonates.
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.
Describe and explain the importance of controlling acidity in the environment (air, water and soil).
Soil - Plants prefer a neutral pH to grow. Air - Can cause acid rain, erodes buildings. Water - Harms the environment.
Describe the preparation, separation and purification of salts using techniques selected from section C2.1 and the reactions specified in section C8.1.
Filtration, evaporation, leave to cool.
Suggest a method of making a given salt from suitable starting material, given appropriate information.
Depends.
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)
2Cu + 2NaOH –> 2NaCuO + H2 NB: Metal + Base –> Salt + Hydrogen Gas Fe(3+) + NaOH –> NaFeO + H2 Fe(3+) + NaOH –> Na(Fe2O3) +
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
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: