Chemistry · Oct / Nov 2023 · Paper 62 · Question 2
0620
As printed in the paper
The question as text
A student investigates the temperature change when aqueous sodium hydroxide neutralises dilute hydrochloric acid. The equation for the reaction is shown. NaOH + HCl → NaCl + H2O The student does six experiments. Experiment 1 ● Fill a burette with dilute hydrochloric acid. ● Run some of the dilute hydrochloric acid out of the burette so that the level of the dilute hydrochloric acid is on the burette scale. ● Fill a second burette with aqueous sodium hydroxide. ● Run some of the aqueous sodium hydroxide out of the burette so that the level of the aqueous sodium hydroxide is on the burette scale. ● Run 1.0 cm3 of dilute hydrochloric acid from the burette into a boiling tube. ● Run 9.0 cm3 of aqueous sodium hydroxide from the second burette into the same boiling tube. ● Stir the mixture with a thermometer and measure the highest temperature reached. ● Measure the pH of the mixture in the boiling tube. ● Rinse out the boiling tube with distilled water. Experiment 2 ● Run 2.0 cm3 of dilute hydrochloric acid from the burette into the boiling tube. ● Run 8.0 cm3 of aqueous sodium hydroxide from the second burette into the same boiling tube. ● Stir the mixture with a thermometer and measure the highest temperature reached. ● Measure the pH of the mixture in the boiling tube. ● Rinse out the boiling tube with distilled water. Experiment 3 ● Repeat Experiment 2 using 3.0 cm3 of dilute hydrochloric acid and 7.0 cm3 of aqueous sodium hydroxide. Experiment 4 ● Repeat Experiment 2 using 6.0 cm3 of dilute hydrochloric acid and 4.0 cm3 of aqueous sodium hydroxide. Experiment 5 ● Repeat Experiment 2 using 7.0 cm3 of dilute hydrochloric acid and 3.0 cm3 of aqueous sodium hydroxide. Experiment 6 ● Repeat Experiment 2 using 8.0 cm3 of dilute hydrochloric acid and 2.0 cm3 of aqueous sodium hydroxide.
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Show the answer and mark scheme
2(a)[4]
M1 all volumes of aqueous sodium hydroxide completed correctly (9.0, 8.0, 7.0, 4.0, 3.0, 2.0)
M2 and M3 all six temperatures completed correctly (26.0; 28.0; 30.0; 30.5; 29.0; 27.5)
M4 all temperatures completed to same number of dp and all volumes of aqueous sodium hydroxide shown to 1 dp
2(b)[5]
M1 appropriate vertical scale so that points and extrapolation to maximum extend over halfway up scale
M2 and M3 all points plotted correctly
M4 two suitable straight lines
M5 straight lines extended so that they cross / meet
2(c)(i)[3]
M1 working shown on graph from where lines cross
M2 volume of dilute hydrochloric acid correct for their graph
M3 volume of aqueous sodium hydroxide correct based on their recorded volume of hydrochloric acid
2(c)(ii)[1]
7
2(c)(iii)[1]
dilute hydrochloric acid
and
(as volume) less / low(er) / small(er) than sodium hydroxide (to be neutral / reach maximum temperature)
2(d)[3]
M1 pH: no change
M2 temperature: higher / greater / bigger
M3 explanation: polystyrene is a better insulator than glass
2(e)[1]
(volumetric) pipettes not available in those sizes / (volumetric) pipettes do not measure variable volumes
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