DP Chemistry (first assessment 2025)

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Question SPM.2.SL.TZ0.3

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Date May Specimen-2023 Marks available [Maximum mark: 7] Reference code SPM.2.SL.TZ0.3
Level SL Paper 2 Time zone TZ0
Command term Determine, Draw, Sketch, Suggest Question number 3 Adapted from N/A
3.
[Maximum mark: 7]
SPM.2.SL.TZ0.3

In a simulation, equal masses of potassium and lithium are added to water and the time taken for the metals to fully react is recorded. Five different increasing masses of each metal are used, and the reaction is timed.

(a)

Sketch the graphs on the axes to show the expected results of this experiment.

[2]

Markscheme

separate curves/lines for Li and K sketched AND both increasing  ✔
steeper gradient for Li
OR
curve/line for Li higher  ✔

(b)

Suggest a reason why comparing the time for complete reaction of equal masses is not a valid measure of reactivity.

[1]

Markscheme

equal masses «of different substances» do not contain equal amounts/moles  ✔

(c)

Lithium carbide, Li2C2, is one of many compounds of lithium and carbon. Determine the percentage covalent character and bonding type in this compound by using sections 9 and 17 of the data booklet.

[2]

Markscheme

«Avg electronegativity = 1.8
Δ electronegativity = 1.6»
% covalent character = 45-55  ✔
ionic  ✔

(d)

Draw the Lewis formula of the anion in the salt Li2C2.

[2]

Markscheme

[:C≡C:]2-
2- charge  ✔
:C≡C:  ✔