Investigate water's specific heat capacity using an electric heater, measured electrical energy and temperature rise; also investigate temperature during melting of crushed ice using a heated water bath.Original labelled apparatus schematic; not to scale. Follow the stated measurements and safety instructions.
For heating water, use a measured water mass in an insulated vessel, immersion heater, joulemeter or voltage/current/time measurements, thermometer or probe and stirrer. A lid reduces heat losses.
For melting, use crushed ice in a beaker supported in a beaker water bath, thermometer/probe, stirrer, stopwatch and a teacher-approved Bunsen heating setup.
Keep electricity dry and the immersion heater submerged as specified by its manufacturer. Do not power a dry heater; take care with hot water, hot glass and Bunsen flames.
Electrical heating and calculation
Find water mass by subtracting empty vessel mass from vessel-plus-water mass. Record mass in kilograms when using specific heat capacity in J/kg/°C.
Place the heater and probe in the water without contact between them. Insulate the sides and use a lid with suitable openings; do not seal a heated vessel under pressure.
Record initial temperature after gentle stirring. Start the energy measurement and heat the water for a known interval, stirring gently so the thermometer represents bulk temperature.
Record final temperature and energy supplied; ΔT = final minus initial temperature. A joulemeter directly measures electrical energy; otherwise E = VIt if voltage and current are approximately constant.
Calculate c = E/(mΔT). The accepted water value is about 4,200 J/kg/°C, but a classroom measured value depends on the method and losses.
Some supplied energy warms the vessel/heater and surroundings. Using all electrical energy as though it heats only the water usually overestimates c.
Measure temperature rise rather than just final temperature. Heating from different initial temperatures changes the energy needed and heat-loss conditions.
Repeat the procedure over comparable intervals or plot supplied energy against temperature rise for fixed water mass. Ideally gradient = mc; losses and apparatus heat capacity can affect the measured slope.
Melting ice and temperature–time graphs
Use a suitable amount of crushed ice and place the sample beaker in a heated water bath. Put the probe in contact with the sample rather than measuring the bath's temperature.Melting-ice setup: the sample beaker sits in a heated water bath. Record sample temperature, not bath temperature, at regular times.
Record sample temperature at regular time intervals while stirring carefully. Keep heating conditions reasonably steady and note when ice remains and when all has melted.
During melting of pure ice at normal atmospheric pressure, temperature stays approximately 0°C while solid and liquid coexist. Energy changes the arrangement of particles instead of raising temperature.
After all the ice melts, continued heating raises the water’s temperature. Draw a temperature–time graph and identify the melting region. Real readings may vary because different parts of the sample have different temperatures or because impurities are present.
A flat section (plateau) can show a change of state under suitable conditions. Energy is still being transferred. To calculate latent heat as well, you would need to measure the energy absorbed during melting and the mass of ice melted.
Crushed ice helps temperature equalise. Avoid a probe touching the vessel or exposed to hot bath water; stir consistently and use a suitable measurement interval.
Precision and evaluation
Check or calibrate temperature probes, read scales at eye level and record times consistently. A temperature change uses two readings. If a thermometer always reads 2 °C too high, that error cancels when you subtract. If its scale is wrong, for example each 1 °C change reads as 1.1 °C, the error may not cancel.
Increase a small temperature rise to reduce relative reading uncertainty, while recognising that longer heating and higher temperatures increase heat losses. Insulation reduces rather than eliminates losses.
Use the same heater position and stirring procedure in repeat trials. A local hot spot gives an unrepresentative temperature rise and can underestimate calculated c.
Distinguish mass, temperature, energy and their units in all workings. State why an improvement addresses a specific loss or measurement problem, rather than just asking for more accurate equipment.
Exam skills: planning, precision and evaluation
State what you change (the independent variable), what you measure (the dependent variable) and what you keep the same (control variables). Explain how you keep each control variable constant, rather than just saying “make it fair”.
Accuracy means how close a result is to the true value. Precision means how close repeated measurements are to each other. Resolution is the smallest change an instrument can show. More digits on a display do not automatically mean a more accurate result.
Repeat measurements for each condition, calculate a mean and describe how spread out the results are. This helps assess and reduce the effect of random errors. Repeating cannot fix an error that pushes results consistently in one direction (a systematic error), such as unaccounted heat loss included in the energy assigned to water.
Repeatability means getting similar results when the same person repeats the same method with the same equipment. Reproducibility means getting similar results when someone else, or different suitable equipment, repeats the experiment. Results can be consistent but still inaccurate.
Check that instruments read zero correctly and are calibrated where needed. Read scales at eye level: looking from an angle can give a wrong reading (parallax error). Choose suitable ranges, measurement intervals and scale divisions (resolution).
Write down the original readings straight away in a table, with units in the headings. Use decimal places that match the instrument’s resolution. Keep the original data and round only when needed. Do not discard a result just because it differs from your prediction.
An anomalous result does not fit the pattern of the other results. Repeat that measurement and check the method. Only leave it out of a mean if you have a clear reason; state which result you excluded and why.
For continuous variables, plot the independent variable on the horizontal axis and the dependent variable vertically. Use sensible scales, units and a best-fit line or curve; do not automatically join every point or force the graph through zero.
Find the gradient of a straight best-fit line using a large triangle: vertical change ÷ horizontal change. For a curve, draw a tangent to estimate the gradient at one point. Explain what the gradient shows in this experiment, include its units and use measured values to support your conclusion.
Uncertainty describes the possible range around a measurement. For one reading on a scale, half the smallest division is a useful classroom estimate unless the question says otherwise. If you subtract two readings, both have uncertainty. Percentage uncertainty = absolute uncertainty ÷ measured value × 100. Follow the method specified in the question.
Use results as evidence and then explain what they mean. A pattern linking variables (a correlation) does not prove that one causes the other. If the ranges of repeat results overlap, a claimed difference may be less convincing. Keep conclusions within the range tested and suggest an improvement that tackles a specific error.
Mr Kidman's Classroom