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1PH0 · CP14.11 (melting ice)Core practical investigationsCore

CP14.11: The Melting-Ice Temperature–Time Graph

Place the crushed-ice sample in the approved arrangement and use the water bath to transfer energy to it. Record sample temperature with a suitably positioned thermometer at fixed time intervals as melting proceeds. The bath temperature is not automatically the sample temperature. Follow the centre’s heating, glassware and hot-water precautions.

35 min Video by Science School Core practical investigations
Edexcel Core Practical 9-1 GCSE P14.11 Properties of water temperature time graph for melting iceCurated by Kepler, not produced by us. Watch it before the notes below.
Open on YouTube

Before you start

  • Use your teacher’s tier checklist: this overview can include Higher-only material, and is not a tier-specific revision list.
  • Pearson Edexcel separate GCSE Physics 1PH0. Use the original core-practical reference and retain every specified subpart; two guides can develop different parts of one core reference.
  • Recall particle arrangements in solids and liquids and the distinction between temperature and internal energy.
  • Use the centre’s approved supervised method and equipment limits. These notes prepare you to explain and evaluate practical work; they do not replace carrying it out and recording the evidence.

Watch, pause, try

Video by Science School. This demonstration is specifically about the Pearson melting-ice graph. It is the phase-change part of CP14.11; the separate water heat-capacity guide covers the other required part.

Viewing focus: Record temperatures while ice changes state in a water bath

After watching, attempt these questions before opening the answers. You can also use the written lesson below.

After watching 1: Explain why a nearly flat graph while ice remains does not imply that heating has stopped.

Show answer and reasoning

Energy can change the solid–liquid arrangement and internal potential energy while temperature stays nearly constant.

After watching 2: Why must you observe the sample state as well as recording temperatures?

Show answer and reasoning

The presence of ice and liquid supports interpreting a near-plateau as melting. Temperature drift alone cannot identify every physical process or measurement fault.

What you'll be able to do

  • Record temperatures while ice changes state in a water bath
  • Explain a near-constant-temperature melting interval
  • Distinguish a temperature graph from a latent-heat measurement
1

Measure the sample rather than only the bath

Place the crushed-ice sample in the approved arrangement and use the water bath to transfer energy to it. Record sample temperature with a suitably positioned thermometer at fixed time intervals as melting proceeds. The bath temperature is not automatically the sample temperature. Follow the centre’s heating, glassware and hot-water precautions.

Use the specified Bunsen-heated water bath where required, and keep the probe in representative contact with the sample without resting it on a hotter vessel surface. Record observations of remaining ice alongside times and temperatures. Do not silently omit an unexpected reading; note a possible probe-position or timing problem and use repeats to assess it.

The CP14.11 instructions specify a thermometer recording crushed-ice temperature as it melts using a Bunsen burner and a beaker-of-water bath. Preserve that required method alongside the separate joulemeter-based water heat-capacity determination.

2

Explain the melting interval microscopically

During ideal melting of a pure substance at constant pressure, energy can increase the internal energy by changing particle arrangement without increasing temperature. In the school model, the average kinetic-energy indicator stays approximately constant while energy increases the potential part associated with separating particles from the solid structure. Melting does not split water molecules into hydrogen and oxygen.

A temperature–time graph can therefore show a near-flat interval while ice and water coexist, followed by a rise once the ice has melted and the liquid warms. Real readings may drift because of thermal gradients, impurities, sensor lag or changing contact. A perfectly horizontal segment should not be forced onto data that do not support it.

Time / sSample temperature / °CSample observation
00.0Ice and water
600.1Ice and water
1200.2Ice and water
1800.3Some ice remains
2401.0Liquid after melting
3005.0Liquid warming
3609.0Liquid warming
Scroll horizontally to see the full code or table.
Original illustrative sample readings with a small melting-region drift. They are not a prescribed dataset or a perfectly uniform-temperature model.

Interpret a melting interval and subsequent warming

Compare an interval while ice remains with a later liquid-warming interval. Does a nearly flat temperature graph mean zero energy transfer?

Sample temperature: Temperature / °C against Time / sData points are joined by straight guides. A dashed line joins the two selected measurements. Use the selectors below to read values and compare intervals; this line gives an average gradient, not an instantaneous tangent.906.75904.51802.252700360Time / sTemperature / °C

Blue: data with straight joining guides. Gold: selected interval. Scroll the plot horizontally on a small screen.

Try Δy ÷ Δx on paper first. Keep the sign and use the units on the axes.

A secant gives average temperature change per second, not heat-transfer power. Relate each interval to the sample observations and recognise the model’s real-measurement limitations.
3

Keep the graph inference within the measured quantities

The duration of a plateau depends on sample mass, transfer rate and losses. A temperature–time graph alone does not determine a numerical specific latent heat. That would also require a suitable measurement of the energy transferred to the changing sample and the mass that changes state, with other energy transfers evaluated.

An average temperature gradient can be calculated for a chosen interval, but it must not be called the heat-transfer rate without a further energy model. A near-zero slope during melting does not mean zero energy input. Compare the graph with the observed phase state and describe a targeted improvement such as more representative probe placement or smaller consistent time intervals near the transitions.

4

Worked applications

Attempt these problems on paper before opening the worked reasoning. Explain your steps as well as giving a final answer.

Example 1A sample is 0.1 °C at 60 s and 0.3 °C at 180 s while visible ice remains. Find the average temperature gradient and interpret it cautiously.
1ΔT = 0.3 − 0.1 = 0.2 K.
2Δt = 180 − 60 = 120 s.
3Gradient = 0.2/120 ≈ 0.00167 K s⁻¹.
Answer
A small positive drift, approximately 0.00167 K s⁻¹; it does not show that energy transfer stopped.
Example 2After the ice has melted, the sample rises from 1.0 to 7.0 °C in 90 s. Find the signed average temperature gradient.
1ΔT = 7.0 − 1.0 = 6.0 K.
2Gradient = 6.0/90.
Answer
+0.0667 K s⁻¹ during the stated warming interval.
Example 3Two melting samples show 180 s and 240 s near-plateau intervals. Can their specific latent heats be ranked from these times alone?
1Sample masses may differ.
2Input rates and transfers to vessels/surroundings may differ.
3A latent-heat calculation needs relevant energy and mass information, not time alone.
Answer
No; the plateau durations do not isolate a material property without the additional measurements and controls.

Common mistakes to avoid

Saying a plateau means no energy transfer.
Explain the internal-energy change during melting.
Calling temperature gradient a power without an energy model.
Keep K s⁻¹ distinct from J s⁻¹.

Key takeaways

  • You can record temperatures while ice changes state in a water bath.
  • You can explain a near-constant-temperature melting interval.
  • You can distinguish a temperature graph from a latent-heat measurement.

Apply it in an exam

Question 1: Two melting samples show 180 s and 240 s near-plateau intervals. Can their specific latent heats be ranked from these times alone?

Show answer and reasoning

No; the plateau durations do not isolate a material property without the additional measurements and controls.

  • Sample masses may differ.
  • Input rates and transfers to vessels/surroundings may differ.
  • A latent-heat calculation needs relevant energy and mass information, not time alone.

Explore further

Return to this tomorrow

Close the notes and answer from memory. Revisit any explanation you cannot yet reconstruct.

  • Which temperature should the sample graph use?
  • What is additionally needed to determine specific latent heat numerically?

Test yourself

Answer a few questions, then review anything you missed.

Next step

Keep practising

Start with the quiz above to check the key ideas. You can also choose another topic from the practice library.

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