DP Chemistry (last assessment 2024)

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Question 19M.2.hl.TZ1.7

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Date May 2019 Marks available [Maximum mark: 2] Reference code 19M.2.hl.TZ1.7
Level hl Paper 2 Time zone TZ1
Command term Formulate Question number 7 Adapted from N/A
7.
[Maximum mark: 2]
19M.2.hl.TZ1.7

An aqueous solution of silver nitrate, AgNO3 (aq), can be electrolysed using platinum electrodes.

Formulate the half-equations for the reaction at each electrode during electrolysis.

Cathode (negative electrode):

Anode (positive electrode):

[2]

Markscheme

Cathode (negative electrode):
Ag+ (aq) + e− → Ag (s)    [✔]


Anode (positive electrode):
2H2O(l) → O2 (g) + 4H+ (aq) + 4e−    [✔]

 

Note: Accept 4OH− (aq) → O2 (g) + 2H2O(l) + 4e−

Accept multiple or fractional coefficients in both half-equations.

Examiners report

Very few answers were correct, even for stronger candidates. Many failed to formulate the correct half equation for the reaction at the anode and used the nitrate ion instead of oxidation of H2O. Some candidates lost one of the marks for using equilibrium arrows in an electrolysis equation.

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