Essential Chemistry Practicals: Salts, Titration & Electrolysis

Required Practical 1: Making Soluble Salts

Aim

To prepare a pure, dry sample of a soluble salt from an insoluble base, for example, making copper(II) sulfate from copper(II) oxide.

Method

1. Add excess copper(II) oxide to warm sulfuric acid and stir.
2. Filter the solution to remove the excess, unreacted base.
3. Gently evaporate the water from the filtrate to crystallize the salt.
4. Leave the solution to cool and then dry the resulting crystals.

Key Points to Remember

• Ensure excess base is used to neutralize all the acid.
• Avoid boiling the solution; use gentle heating to prevent it from spitting.
• Filter carefully to remove all unreacted solid for a pure salt solution.

Required Practical 2: Neutralization by Titration

Aim

To determine the concentration of an acid or an alkali using a titration.

Method

1. Use a pipette to accurately measure a known volume of alkali into a conical flask.
2. Add a few drops of a suitable indicator, such as phenolphthalein.
3. Slowly add acid from the burette, swirling the flask continuously, until the indicator changes color permanently.
4. Record the final volume of acid used from the burette.

Key Points to Remember

• Always rinse the equipment first with distilled water and then with the solution it will contain.
• Ensure the burette is read at eye level from the bottom of the meniscus.
• Repeat the titration until you achieve concordant results (readings within 0.10 cm³ of each other).

Required Practical 3: Electrolysis of Aqueous Solutions

Aim

To investigate the products formed during the electrolysis of different aqueous salt solutions, such as sodium chloride and copper(II) sulfate.

Method

1. Set up the electrolysis circuit using inert graphite electrodes.
2. Add the chosen salt solution to a beaker.
3. Switch on the power supply and observe any gas production or deposits at each electrode.
4. Test any gases produced. For example, hydrogen gives a 'squeaky pop' with a lit splint, while chlorine bleaches damp litmus paper.

Key Points to Remember

• At the cathode (negative electrode), hydrogen gas is produced if the metal in the salt is more reactive than hydrogen.
• At the anode (positive electrode), oxygen or a halogen (like chlorine) is formed, depending on the ions present in the solution.
• You should be able to write the half-equations for the reactions occurring at each electrode.

Required Practical 4: Temperature Changes in Reactions

Aim

To investigate the temperature changes that occur during exothermic and endothermic reactions.

Method

1. Measure a set volume of a reactant (e.g., an acid) into an insulated polystyrene cup.
2. Record the initial temperature of the solution.
3. Add a measured amount of the second reactant (e.g., an alkali), stir, and place a lid on the cup.
4. Record the maximum or minimum temperature reached during the reaction.
5. Repeat the experiment with different concentrations or reactants to compare the energy changes.

Key Points to Remember

• Use a lid on the polystyrene cup to reduce heat loss to or heat gain from the surroundings.
• Ensure accurate and precise temperature readings are taken.
• Plot a graph of the temperature change against the variable being tested (e.g., concentration).