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To investigate the thermal properties of water, students placed hot water in two thin plastic cups and measured their rate of cooling. The sides of one cup were covered with tissue paper soaked in hot water; the other cup was left uncovered. The temperature was recorded with a thermometer every 4 minutes for 20 minutes. The temperature in the laboratory was 18 °C.
[Source: © International Baccalaureate Organization 2017]
[Source: © International Baccalaureate Organization 2017]
Calculate the change in temperature in each cup after 20 minutes.
Uncovered:
Covered with wet tissue paper:[1]
State two conditions that must be the same for each cup at the start of the experiment.[2]
Predict the temperature of the water in the cups after 3 hours.[1]
Explain, with reference to the thermal properties of water, how this experiment helps demonstrate how humans respond to overheating.[3]
Answer/Explanation
Markscheme
uncovered: 50 °C
covered with wet tissue paper: 55 °C
Both needed
Accept range 49 to 51 °C and 54 to 56 °C
Units required
Accept negative numbers (–50 °C and –55 °C)
Working on its own without an answer is insufficient for the mark (eg: 80 – 30)
a. volume/mass/amount of water they contain
b. temperature of water
c. placed in similar environment/on similar surface
OWTTE
d. «container must be» the same shape/size/volume/surface area
Do not award “ambient room temperature” or “material of cups”
Do not accept “type of water”[Max 2 Marks]
18 °C
OR
room temperature
If the answer is given as a numerical value then units are required
a. water has a high latent heat/high heat of vaporization
b. energy required to evaporate water «from the tissue paper»
c. evaporation of water leads to cooling
d. sweat produced by skin in response to heat
e. «evaporation of» sweat cools the body
Do not accept specific heat[Max 3 Marks]