Question 119 marks
Question
You are going to investigate the temperature change when anhydrous lithium chloride dissolves in water. Read all of the instructions carefully before starting the experiments. Instructions You are going to do five experiments. Experiment 1 • Use the 50 cm3 measuring cylinder to pour 40 cm3 of distilled water into the 100 cm3 beaker. • Use the thermometer to measure the initial temperature of the water. Record this initial temperature in Table 1.1. • Add a 2.0 g sample of anhydrous lithium chloride to the water in the beaker. • Continually stir the mixture in the beaker using the thermometer. • Measure the highest temperature reached by the mixture in the beaker. Record this highest temperature of the mixture in Table 1.1. • Empty the beaker and rinse the beaker with distilled water. Experiment 2 • Repeat Experiment 1 using 30 cm3 of distilled water instead of 40 cm3. Experiment 3 • Repeat Experiment 1 using 25 cm3 of distilled water instead of 40 cm3. Experiment 4 • Repeat Experiment 1 using 20 cm3 of distilled water instead of 40 cm3. Experiment 5 • Repeat Experiment 1 using 15 cm3 of distilled water instead of 40 cm3. (a) Complete Table 1.1. Table 1.1 mass of initial highest anhydrous volume of temperature experiment temperature temperature lithium chloride water / cm3 change / °C / °C reached / °C /g 1 2.0 40 2 30 3 25 4 20 5 15 [5] (b) Complete a suitable scale on the y-axis and plot your results from Experiments 1 to 5 on Fig. 1.1. Draw a line of best fit. temperature change / °C 0 10 15 20 25 30 35 40 45 volume of water / cm3 Fig. 1.1 [4] (c) Extrapolate the line on your graph in Fig. 1.1 to deduce the temperature change when Experiment 1 is repeated with 45 cm3 of water instead of 40 cm3 of water. Show clearly on Fig. 1.1 how you worked out your answer. temperature change = …… [3] (d) The energy, in J, given out when 2.0 g of anhydrous lithium chloride dissolves is calculated using the equation shown. energy given out = temperature change × 4.2 × volume of water Calculate the energy given out when 2.0 g of anhydrous lithium chloride dissolves in Experiment 5. energy given out = …… J [1] (e) Estimate the temperature change when Experiment 1 is repeated using 4.0 g of anhydrous lithium chloride instead of 2.0 g. Give a reason for your answer. temperature change …… reason …… [2] (f) Explain why the results obtained would be more accurate if the beaker used in each experiment was replaced by a polystyrene cup. …… [2] (g) (i) Explain why using a burette instead of a measuring cylinder is an improvement. …… [1] (ii) Explain why standing the beaker in a water-bath is not an improvement. …… [1] [Total: 19]
Mark scheme
1(a) initial and final temperatures recorded for all five experiments and all experiments have a mass of 2.0 g of lithium chloride 1 all temperature readings and calculated temperature changes are to same precision 1 all temperature changes calculated correctly 1 temperature changes continually increase down table 1 temperature change for experiment 1 is approximately half the change for experiment 4 1 1(b) y-axis scale is linear and points extend over halfway up scale 1 all points plotted correctly 2 best fit line 1 1(c) extrapolation shown on graph, this must be a smooth continuation of line to at least a volume of 45 1 correct reading from their extrapolation at 45 1 °C 1 1(d) correct evaluation of experiment 5: 1 ∆T × 4.2 × 15 1(e) temperature change which is twice temperature change stated in table for Experiment 1 1 twice as much lithium carbonate dissolved / used (so twice as much energy given out) 1 1(f) polystyrene is a better insulator than glass / it is an insulator 1 less heat loss (to the surroundings) 1 1(g)(i) (burette more) accurate (than measuring cylinder) 1 1(g)(ii) water-bath would keep temperature constant 1