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Date November 2017 Marks available 1 Reference code 17N.3.sl.TZ0.1
Level SL Paper 3 Time zone TZ0
Command term Suggest Question number 1 Adapted from N/A

Question

A student set up a simple voltaic cell consisting of a copper electrode and a zinc electrode dipped in sodium chloride solution.

The student gradually increased the distance, d, between the electrodes to study the effect on the initial current, I, passing through the light bulb.

The student hypothesized that the initial current would be inversely proportional to the distance between the electrodes.

The following data was collected over five trials.

The data did not support the student’s hypothesis. He investigated other possible relationships by plotting a graph of the average current against the distance between the electrodes. He obtained the following best-fit line with a correlation coefficient (r) of −0.9999.

Sketch a graph that would support the student’s hypothesis.

[1]
a.

Suggest what the correlation coefficient of −0.9999 indicates.

[1]
b.i.

State the equation of the straight line obtained using the data.

[1]
b.ii.

Outline how current flows in the sodium chloride solution.

[1]
b.iii.

Markscheme

OR

OR

Correct labels of axes required for mark.

Accept d–1 instead of  1 d .

Accept I–1 instead of 1 I .

Plot of I vs d should not be linear.

a.

negative correlation

OR

model/prediction matches results

OR

99% of variance accounted for

b.i.

I = – 0.001631 d + 0.09939

OR

y = – 0.001631 x + 0.09939

Accept correctly rounded values for m and b in equation.

Do not accept “y = mx + b”.

b.ii.

ions move «across electrolyte»

b.iii.

Examiners report

[N/A]
a.
[N/A]
b.i.
[N/A]
b.ii.
[N/A]
b.iii.

Syllabus sections

Core » Topic 11: Measurement and data processing » 11.2 Graphical techniques
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