Year 7 Science · Unit 4 · Lesson 6
Master Worksheet
Learning Goals
Find the error: Leo’s report
Leo’s report
Question: does the number of layers of cloth wrapped around a cup of hot water affect how much the water cools in 10 minutes? (1) Independent variable: the temperature drop of the water after 10 minutes. (2) Controlled variables: the same cup, the same starting temperature and the same volume of water. (3) In my results table I wrote the unit next to every number, like 22 °C, 16 °C. (4) On my line graph I put the temperature drop along the bottom and the number of layers up the side. (5) Conclusion: wrapping cups is a good idea.
1. Four of Leo’s five numbered sentences contain an error. For each one, give its number and rewrite it correctly.
Read the data: wrapping a cup of hot water
Scenario
Leo corrected his report and repeated the experiment. Each cup started with 200 mL of water at 70 °C. He measured how much the temperature dropped in 10 minutes, three times for each number of layers.
| Layers of cloth | Trial 1 | Trial 2 | Trial 3 | Average |
|---|---|---|---|---|
| 0 | 22 | 21 | 23 | 22 |
| 1 | 16 | 17 | 15 | 16 |
| 2 | 12 | 13 | 5 | |
| 3 | 10 | 9 | 11 | 10 |
| 4 | 9 | 9 | 9 | 9 |
Source: sample class results.
2. Identify the result in Table 1 that does not fit the pattern (an anomalous result) and suggest one thing that could have caused it.
3. Calculate the average for 2 layers, leaving out that result.
Answer °C
4. Plot the averages on the grid, using your answer to Question 3 for 2 layers. Label both axes with names and units, and draw a smooth trend line.
5. Describe the trend, including how the shape of the line changes. Then write a conclusion that answers Leo’s question, using data.
Plan an investigation: sugar and water temperature
A classmate claims: “The warmer the water, the faster a teaspoon of sugar dissolves in it.” Plan a fair test of this claim. The number in brackets is the marks for each part.
Testable prediction (1)
If … then …
Variables (3)
Method (3)
Results table: write the headings with units, and fill in the first column (2)
6. Evaluate this statement: “Measuring the dissolving time only once at each temperature is enough to be sure of the trend.” Use evidence from Leo’s results in Table 1.
Find the error: Leo’s report
1. (1) The independent variable is the number of layers of cloth; the temperature drop is the dependent variable (1). (2) is correct. (3) Write the unit once, in the column heading, e.g. “Temperature drop (°C)” (1). (4) Number of layers (independent) along the bottom, temperature drop up the side (1). (5) The conclusion must answer the question with the trend and data, e.g. more layers gave a smaller drop (1). [4 marks]
Read the data: wrapping a cup of hot water
2. Trial 3 at 2 layers, 5 °C (1). Cause, e.g. read the thermometer too early, a lid was left on, or the water started cooler (1). [2 marks]
3. (12 + 13) ÷ 2 (1) = 12.5 °C (1). [2 marks]
4. “Layers of cloth” across, “Temperature drop (°C)” up (1); five averages plotted: 22, 16, 12.5, 10, 9 (1); a smooth curve, not joined dot-to-dot (1). [3 marks]
5. Decreasing: more layers, smaller drop (1). Steep at first (22 to 16 °C for the first layer), then levelling off (10 to 9 °C from 3 to 4 layers) (1). Conclusion: yes, more layers reduced the cooling, from 22 °C with none to 9 °C with four (1). [3 marks]
Plan an investigation: sugar and water temperature
Prediction: if the water is warmer, then the sugar will dissolve in less time (1). Independent: water temperature, e.g. 20, 40, 60, 80 °C (1); dependent: time to dissolve, in seconds (1); controlled, two of: volume of water, amount and type of sugar, stirring, cup (1). Method: heat the water to each temperature and check it with a thermometer (1); add one level teaspoon of sugar and start the stopwatch (1); stop it when no crystals remain; repeat three times at each temperature (1). Table: Water temperature (°C) | Trial 1 (s) | Trial 2 (s) | Trial 3 (s) | Average (s) (1); four temperatures in column 1 (1). [9 marks]
Question 6
Marking guide: 1 disagree; 1 a single result could be a mistake and you could not tell; 1 Table 1: trial 3 at 2 layers (5 °C) would have wrecked the trend if it were the only result; 1 repeating shows anomalies, which can be left out; 1 averages of repeats give more reliable values; 1 so the trend and conclusion can be trusted. [6 marks]
Model answer: I disagree. One result could be a slip, and you would not know. In Leo’s Table 1, trial 3 at 2 layers gave 5 °C; alone, it would make 2 layers look better than 4. Because he repeated, the other trials (12 and 13 °C) showed it was an anomaly. Averages of repeats are more reliable, so the trend and conclusion can be trusted.
Common error: averaging the anomaly in (10 °C for 2 layers), which bends the curve.