Required Practical 2: Enthalpy change
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Explain how you could improve the standard method of measuring enthalpy change and explain how you could measure the temperature change (6 marks)
Apparatus: • Use a burette/pipette (instead of a measuring cylinder) • Use a polystyrene cup (instead of a beaker) / insulate beaker • Reweigh the watch glass after adding the solid • Use powdered solid Temperature Measurements: • Measure and record the initial temperature of the solution for a few minutes before addition • Measure and record the temperature after the addition at regular intervals (eg each minute) for 8+ minutes/until a trend is observed Temperature Determination: • Plot a graph of temperature against time • Extrapolate to the point of addition • Determine ΔT at the point of addition
Explain how you could reduce percentage uncertainty of using the thermometer (2 marks)
• Increase the magnitude of temperature change - By increasing the concentration of the acid/alkali added
Outline a simple practical experiment including the measurements to be taken, in order to determine the enthalpy of combustion for an unknown alcohols (5 marks)
• Weigh the spirit burner (alcohol) before and after combustion • Water in a calorimeter / beaker • Measure volume of water (or mass) • Burn the alcohol to heat the water • Measure temperature rise in water
Suggest one improvement that would reduce errors due to heat loss in the student’s experiment (1 mark)
• Reduce the distance between the flame and the beaker • Put a sleeve around the flame to protect from drafts • Add a lid