Chemistry · Oct / Nov 2020 · Paper 61 · Question 2
0620
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The question as text
A student investigated the mass of lead(II) iodide precipitate formed when aqueous potassium iodide reacts with aqueous lead(II) nitrate. The equation for the reaction is shown. 2KI(aq) + Pb(NO3)2(aq) → PbI2(s) + 2KNO3(aq) The student did seven experiments. Experiment 1 ● Using a 50 cm3 measuring cylinder, 25 cm3 of aqueous potassium iodide was poured into a beaker. ● Using a clean 50 cm3 measuring cylinder, 10 cm3 of aqueous lead(II) nitrate was added to the aqueous potassium iodide in the beaker. The solutions were mixed together. ● The mass of the precipitate of lead(II) iodide formed was found. Experiment 2 ● Experiment 1 was repeated using a larger volume of aqueous lead(II) nitrate than in Experiment 1. Experiment 3 ● Experiment 1 was repeated using a larger volume of aqueous lead(II) nitrate than in Experiment 2. Experiment 4 ● Experiment 1 was repeated using a larger volume of aqueous lead(II) nitrate than in Experiment 3. Experiment 5 ● Experiment 1 was repeated using a larger volume of aqueous lead(II) nitrate than in Experiment 4. Experiment 6 ● Experiment 1 was repeated using a larger volume of aqueous lead(II) nitrate than in Experiment 5. Experiment 7 ● Experiment 1 was repeated using a larger volume of aqueous lead(II) nitrate than in Experiment 6.
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2(a)[2]
Measuring cylinder readings:
16; 23; 29; 39; 44; 48
2(b)[5]
M1 and M2 all points plotted correctly
M3 ruler drawn straight line through first 4 points
M4 ruler drawn straight line through last three points
M5 straight lines have been extended so that they meet / cross
2(c)[2]
working on graph
correct reading from their working on graph
2(d)[1]
all potassium iodide reacted / used-up
2(e)[2]
maximum mass of precipitate is 2.55 g
maximum mass reached at half volume of plotted graph
2(f)(i)[1]
(more) accurate / precise (than a measuring cylinder)
2(f)(ii)[1]
(pipette measures a) fixed volume / 25 cm3
2(g)[3]
filter
wash / rinse residue
dry and weigh
Tests on solid Y
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