A student used the apparatus in Fig. 4.1 to find the temperature rise produced when ethanol burns. She placed 100 cm3 of water in a metal can, recorded its ...
Question 1 Report
A student used the apparatus in Fig. 4.1 to find the temperature rise produced when ethanol burns. She placed 100 cm3 of water in a metal can, recorded its temperature, then lit the spirit burner and let it heat the water. She recorded the final temperature of the water and the mass of the burner before and after burning. The results are in Table 4.1.
Table 4.1
| measurement | reading |
|---|---|
| temperature of water at start /℃ | 18.0 |
| temperature of water at end /℃ | 46.5 |
| temperature rise /℃ | to be calculated |
| mass of burner + ethanol at start /g | 84.20 |
| mass of burner + ethanol at end /g | 83.15 |
| mass of ethanol burned /g | to be calculated |
(a) Complete Table 4.1 by calculating the temperature rise and the mass of ethanol burned. [2]
(b) Name a piece of apparatus that could be used to measure 100 cm3 of water. [1]
(c) Suggest why a metal can is used to hold the water instead of a glass beaker. [1]
(d) State whether the combustion of ethanol is exothermic or endothermic. [1]
(e) State two ways in which heat is lost so that not all the energy heats the water. [2]
(f) Describe two improvements that would give a more accurate result. [2]
(g) State one variable that must be kept the same to make a fair comparison with another fuel. [1]
Answer Details
Burning a fuel releases heat, which is used here to warm water in a metal can. You measure the temperature rise of the water and the mass of fuel burned so that the energy transferred can be compared between fuels.
(a) Temperature rise and mass of ethanol burned [2]:
\[ \Delta T = 46.5 - 18.0 = 28.5\ \text{℃} \]\[ m_{\text{ethanol}} = 84.20 - 83.15 = 1.05\ \text{g} \]so a rise of 28.5 ℃ [1] and 1.05 g of ethanol burned [1].
(b) To measure 100 cm3 of water use a measuring cylinder [1].
(c) A metal can is used because metal conducts heat better than glass, so more heat passes from the flame to the water [1].
(d) Combustion of ethanol is exothermic [1]: it gives out heat, shown by the rise in water temperature.
(e) Two ways heat is lost (any two) [2]: heat lost to the surrounding air [1]; heat lost through the sides of the can, by evaporation of water, or by incomplete combustion (accept heat used to warm the can and thermometer) [1].
(f) Two improvements for a more accurate result (any two) [2]: use a lid or draught shield to reduce heat loss [1]; insulate the can, or hold the burner a fixed distance below the can, or stir the water, or repeat and average [1].
(g) One variable to keep the same for a fair comparison with another fuel: the volume (or mass) of water heated (accept the starting temperature, or the distance of the flame below the can) [1].
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