Redox Equilibria | Edexcel International A Level Chemistry Multiple Choice Questions 2017

11 mark

The standard hydrogen electrode uses an electrode of platinum coated in a finely divided form of the metal called platinum black.

What is the purpose of this coating?

to increase the rate of the equilibrium between the hydrogen gas and the hydrogen ions
to provide an inert protective coating for the electrode
to increase the electrical conductivity of the electrode
to ensure that the conditions remain standard

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1a1 mark

An electrochemical cell is made from the electrode systems shown by these half‐equations.

Ag⁺(aq) + e⁻ ⇌ Ag (s) $E^{⦵}$ = +0.80V

V $O_{2}^{+}$ (aq) + 2H⁺(aq) + e⁻ ⇌ VO²⁺ (aq) + H₂O (l) $E^{⦵}$ = +1.00V

The apparatus used to measure the value for $E_{cell}^{⦵}$ under standard conditions is shown.

q3-paper-5-jan-2022-edexcel-ial-chemistry

a)

Which silver compound could be used as the electrolyte in the left‐hand half‐cell?

silver nitrate
silver hydroxide
silver chloride
silver carbonate

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1b1 mark

b)

The electrolyte in the right‐hand half‐cell is prepared using equal volumes of

1 mol dm⁻³ acidified VO₂⁺(aq) and 1 mol dm⁻³ acidified VO²⁺(aq)
2 mol dm⁻³ acidified VO₂⁺ (aq) and 2 mol dm⁻³ acidified VO²⁺(aq)
1 mol dm⁻³VO₂⁺ (aq) and 1 mol dm⁻³ HCl (aq)
1 mol dm⁻³ VO²⁺(aq) and 1 mol dm⁻³ HCl (aq)

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1c1 mark

c)

Which is the equation for the overall cell reaction under standard conditions?

VO²⁺(aq) + Ag⁺(aq) + H₂O(l) $\to$ ${VO}_{2}^{+} (aq)$ + Ag(s) + 2H⁺(aq)
${VO}_{2}^{+} (aq)$ + Ag(s) + 2H⁺(aq) $\to$ VO²⁺(aq) + Ag⁺(aq) + H₂O(l)
VO²⁺(aq) + 3Ag(s) + 2H⁺(aq) $\to$ ${VO}_{2}^{+} (aq)$ + 3Ag⁺(aq) + H₂O(l)
${VO}_{2}^{+} (aq)$ + 3Ag⁺(aq) + H₂O(l) $\to$ VO²⁺(aq) + 3Ag(s) + 2H⁺(aq)

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1d

1 mark

d)

Which is the value of

E_{cell}^{⦵}

in volts?

−1.80
−0.20
+0.20
+1.80

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1e1 mark

Which is the cell diagram for this cell, using the conventional representation of half‐cells?

Ag(s) | Ag⁺(aq) || [ ${VO}_{2}^{+} (aq)$ + 2H⁺(aq)] | [VO²⁺(aq) + H₂O(l)] | Pt(s)
Ag(s) | Ag⁺(aq) || [ ${VO}_{2}^{+} (aq)$ + 2H⁺(aq)] , [VO²⁺(aq) + H₂O(l)] | Pt(s)
Ag(s) | Ag⁺(aq) || [ VO²⁺(aq) + H₂O(l)] | [ ${VO}_{2}^{+} (aq)$ + 2H⁺(aq)] | Pt(s)
Ag(s) | Ag⁺(aq) || [ VO²⁺(aq) + H₂O(l)] , [ ${VO}_{2}^{+} (aq)$ + 2H⁺(aq)] | Pt(s)

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1a1 mark

The apparatus shown was used to measure the standard electrode potential for the reduction of Cr_{2 $O_{7}^{2 -}$}ions to Cr³⁺ ions in acid solution:

Cr_{2 $O_{7}^{2 -}$}(aq) + 14H⁺(aq) + 6e^–→ 2Cr³⁺(aq) + 7H₂O(l)

q1-paper-5-oct-2021-edexcel-ial-chemistry

a)

Which material should be used for each electrode?

		Electrode 1	Electrode 2
☐	A	Na₂Cr₂O₇	Cr₂O₃
☐	B	H₂	Cr
☐	C	Pt	Cr
☐	D	Pt	Pt

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1b1 mark

b)

Solution 1 is

0.33 mol dm^–3H₃PO₄(aq)
0.50 mol dm^–3 H₂SO₄(aq)
1.00 mol dm^–3HCl (aq)
1.00 mol dm^–3 CH₃COOH (aq)

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1c

1 mark

c)

Solution 2 contains 14.71g of K₂Cr₂O₇ .

What mass of Cr₂(SO₄)₃⋅18H₂O should also be used?

[M_r values: K₂Cr₂O₇ = 294.2 Cr₂(SO₄)₃⋅18H₂O = 716.3]

8.95 g
17.91 g
19.62 g
35.82 g

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1d1 mark

d)

Solution 2 is best acidified with

H₂SO₄
HCl
HBr
H₂CrO₄

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Electrode system	$E^{⦵}$ / V
Bk³⁺ + e^– ⇌ Bk²⁺	–2.80
Cu²⁺ + e^– ⇌ Cu⁺	+0.15
Bk⁴⁺ + e^– ⇌ Bk³⁺	+1.67
Au⁺ + e^– ⇌ Au	+1.69
Au²⁺ + e^– ⇌ Au⁺	+1.80
Ag³⁺ + e^– ⇌ Ag²⁺	+1.80
Ag²⁺ + e^– ⇌ Ag⁺	+1.98
Cu³⁺ + e– ⇌ Cu²⁺	+2.40

		Metals used for the electrode
		Fe³⁺/ Fe²⁺ electrode system	Ti²⁺/ Ti electrode system
□	A	iron	titanium
□	B	iron	platinum
□	C	platinum	titanium
□	D	platinum	platinum

		Concentration of the original solution
		FeSO₄	Fe₂(SO₄)₃
□	A	1 mol dm^–3	0.5 mol dm^–3
□	B	1 mol dm^–3	1 mol dm^–3
□	C	2 mol dm^–3	1 mol dm^–3
□	D	2 mol dm^–3	2 mol dm^–3

Edexcel International A Level Chemistry

Topic Questions

5.1 Redox Equilibria