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RedoxElectrolysisCritA_May2020

Last updated over 5 years ago
25 questions
QUESTIONS (levels adjusted for an open book test)
Strand i. describe scientific knowledge
1

Identify the row with both correct statements for the following electrochemical processes:
[Level 1-2]




1

Water in swimming pools can be purified using a chlorinating cell, where an aqueous solution of sodium chloride is electrolysed to produce chlorine. Identify the products formed at the anode and cathode.
[Level 5-6]

1

In a voltaic cell the redox reactions occur spontaneously. Which statement(s) accurately describe the processes of a voltaic cell? [Level 1-2]

1

In the electrolysis of molten sodium chloride, sodium ions: [Level 5-6]

1

The reactivity series lists metals in order of reactivity. The most easily oxidised metals can be found
[Level 3-4]

1

Which of the following equations represents the reduction of a metal? [Level 3-4]

For the following half-equations (a and b)
a) Cu(s) → Cu2+(aq) + 2e-
b) Ag+(aq) + e- → Ag(s)
1

i. Identify which is oxidation and which is reduction. [Level 1-2]

1

ii. Combine the half-equations to form a balanced redox equation. [Level 7-8]

Strand ii apply scientific knowledge and understanding to solve problems set in familiar and unfamiliar situations
A student performed the electrolysis of molten lead (II) bromide (PbBr2) using the apparatus show.

henniscience.weebly.com

The student made a number of observations
  • The light bulb did not light up straight away
  • Brown gas was observed at the positive electrode
  • Molten metal was observed at the negative electrode.
1

i. Explain why the bulb did not initially light up. [level 7-8]

1

ii. Write the half-equation for the reaction taking place at the positive electrode [level 5-6]

1

iii. Write the half-equation for the reaction taking place at the negative electrode [level 5-6]

1

iv. Explain why lead is formed at the negative electrode and why this reaction taking place at the negative electrode is viewed as a reduction reaction?
[level 3-4]

The diagram shows a voltaic cell:

Source: Harwood, Richard, and Ian Lodge. Cambridge IGCSE Chemistry Coursebook. Cambridge University Press, 2014.
1

i. State and explain the direction of electron flow in the external circuit. [level 3-4]

1

ii. State and explain whether oxidation or reduction occurs at each electrode. [level 5-6]

1

iii. State which electrode is the cathode and which is the anode. [level 3-4]

1

iv. Explain the function of the salt bridge. [level 7-8]

1

v. Explain whether the voltage will increase or decrease when the nickel half-cell is replaced by a Cu/Cu2+ half-cell. [level 5-6]

iii. analyse information to make scientifically supported judgments.
A student added different metals to solutions of metal ions and recorded the observations

1

i. Identify what is the most reactive metal [level 1-2]

1

ii. Identify what is the least reactive metal [level 1-2]

1

iii. For the metals tested, write a reactivity series, starting with the most reactive.
[level 3-4]

1

iv. With the aid of chemical reactions (half equations and overall balanced equation), explain the observations for the reaction of magnesium with copper sulphate. [level 7-8]

Aluminium metal can be obtained from the redox reaction between aluminium oxide (alumina) and solid carbon. The product of this redox reaction is carbon dioxide.
1

i. Write down a balanced equation for the redox reaction between aluminium oxide and carbon. [level 5-6]

1

ii. Identify the element that is oxidized and the element that is reduced. Justify your answers. [level 7-8]

Using a simple voltaic cell, as shown, a student carried out an experiment to investigate the order of reactivity of tin, nickel and iron.

The following results were obtained:

1

i. Explain why the student decided to have copper as metal X in each experiment?
[level 3-4]

1

ii. List these metals in order of reactivity (most reactive first). [level 3-4]