MDCAT Chemistry chapter 9: Chemistry · Electrochemistry MCQs with answers
By Team Megalecture · Updated 4 Nov 2026
29 exam-style questions on Chemistry · Electrochemistry, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.
Ten Chemistry · Electrochemistry questions with answers
Try each one, then open the answer. These ten stay the same; the test draws new ones every time.
1. A galvanic cell is made from a nickel electrode in 1 M Ni2+ (E° = −0.25 V) and a silver electrode in 1 M Ag+ (E° = +0.80 V). Its standard emf is
A
0.55 V
B
1.85 V
C
1.05 V
D
−1.05 V
Show answer
Answer: C. Silver has the higher E°, so it is the cathode: E°cell = 0.80 − (−0.25) = 1.05 V. E° values are not multiplied by the 2 in 2Ag+ (doing so gives 1.85 V), and 0.55 V ignores the negative sign of nickel.
2. Concentrated aqueous copper(II) chloride is electrolysed between inert carbon electrodes. The products at the cathode and the anode respectively are
A
hydrogen and chlorine
B
copper and chlorine
C
copper and oxygen
D
chlorine and copper
Show answer
Answer: B. Cu2+ (E° = +0.34 V) is reduced much more easily than water, so copper is deposited on the cathode; in a concentrated chloride solution Cl− ions are discharged at the anode as Cl2. Hydrogen forms at the cathode only with ions that are hard to reduce, such as Na+.
3. Galvanised iron is iron coated with zinc. Even where the zinc layer is scratched, the exposed iron does not rust. Given E°: Zn2+/Zn −0.76 V and Fe2+/Fe −0.44 V, the reason is that
A
zinc has the less negative E°, so zinc is reduced in preference to iron
B
zinc has the more negative E°, so zinc is oxidised in preference to iron
C
zinc is less reactive than iron and simply seals the iron off from air and water
D
zinc makes the iron the anode, so the iron gives up its electrons more slowly
Show answer
Answer: B. Where zinc and iron touch in moist air they form a cell in which zinc, with the more negative E°, is the anode: zinc is oxidised (sacrificial protection) and the iron, as the cathode, is not. A coating of a less reactive metal such as tin protects only while it is unbroken.
4. In acid solution nitrate ions are reduced to nitrogen monoxide: NO3− + xH+ + ye− → NO + 2H2O. In the balanced half-equation
A
x = 2, y = 3
B
x = 4, y = 5
C
x = 4, y = 2
D
x = 4, y = 3
Show answer
Answer: D. Nitrogen falls from +5 to +2, so y = 3 electrons, and the four hydrogen atoms in 2H2O need x = 4. Charges check: −1 + 4 − 3 = 0 on the left, 0 on the right.
5. In the cell notation Zn(s) | Zn2+(aq) || Cu2+(aq) | Cu(s), what does the double vertical line (||) stand for?
A
the boundary between a metal and a solution of its ions
B
the external wire through which the electrons flow
C
the voltmeter connected between the two electrodes
D
the salt bridge joining the two half-cells
Show answer
Answer: D. A single line marks a phase boundary, such as between Zn(s) and Zn2+(aq), and the double line marks the salt bridge that links the two solutions. The anode half-cell is written on the left and the cathode half-cell on the right.
6. The cell Mg | Mg2+(1 M) || Cu2+(1 M) | Cu has a standard emf of 2.71 V, and E°(Cu2+/Cu) = +0.34 V. What is E°(Mg2+/Mg)?
A
+2.37 V
B
−3.05 V
C
−2.37 V
D
+3.05 V
Show answer
Answer: C. Magnesium is the anode (left), so E°cell = E°cathode − E°anode: 2.71 = 0.34 − E°(Mg), giving E°(Mg2+/Mg) = −2.37 V. Subtracting the wrong way round (E°(Mg) − 0.34 = 2.71) gives +3.05 V.
7. What is the oxidation number of manganese in potassium permanganate, KMnO4?
A
+6
B
+7
C
+4
D
+2
Show answer
Answer: B. (+1) + x + 4(−2) = 0 gives x = +7, the highest oxidation state of manganese. +6 is manganese in K2MnO4 and +4 in MnO2.
8. Magnesium burns in oxygen: 2Mg(s) + O2(g) → 2MgO(s). What happens to the oxidation numbers?
A
Mg rises from 0 to +2 (reduced); O falls from 0 to −2 (oxidised)
B
Mg rises from 0 to +2 (oxidised); O stays at −2 throughout
C
Mg rises from 0 to +2 (oxidised); O falls from 0 to −2 (reduced)
D
Mg stays at +2 throughout; O stays at −2 throughout
Show answer
Answer: C. Atoms of a free element have oxidation number zero, so both Mg and the O atoms in O2 start at 0. Each Mg loses two electrons to form Mg2+ (oxidation), and each O atom gains two to form O2− (reduction).
9. Equal volumes of 0.1 mol dm−3 hydrochloric acid and 0.1 mol dm−3 ethanoic acid are tested in turn with the same battery and bulb. The bulb glows brightly with the HCl but only dimly with the ethanoic acid because
A
HCl is almost completely ionised, but ethanoic acid is only slightly ionised
B
HCl solution conducts by free electrons, but ethanoic acid conducts by its ions
C
HCl is an ionic compound, but ethanoic acid is a covalent compound
D
ethanoic acid is a non-electrolyte, so only the water in it conducts
Show answer
Answer: A. Current in an electrolyte is carried by mobile ions. HCl is a strong electrolyte that ionises almost completely in water, whereas ethanoic acid is a weak electrolyte, so its solution has far fewer ions to carry the charge. Pure HCl is itself covalent; it forms ions only on reacting with water.
10. A copper electrode in 1 M Cu2+ is joined to the standard hydrogen electrode, and electrons flow through the wire from the hydrogen electrode to the copper. This shows that
A
E°(Cu2+/Cu) is negative; Cu2+ is reduced more easily than H+
B
E°(Cu2+/Cu) is positive; copper is oxidised more easily than H2
C
E°(Cu2+/Cu) is negative; copper is oxidised more easily than H2
D
E°(Cu2+/Cu) is positive; Cu2+ is reduced more easily than H+
Show answer
Answer: D. Electrons arrive at the copper, so Cu2+ + 2e− → Cu happens there and H2 is oxidised at the SHE. A half-cell that is reduced when paired with the SHE has a positive reduction potential (+0.34 V for copper).
Chemistry · Electrochemistry: questions students ask
How many Chemistry · Electrochemistry MCQs are there?
29, each with the answer and a short explanation, across 2 topics: Oxidation numbers and redox, Electrode potentials and cells. Every chapter test draws ten of them, so you can take it many times.
Is the MDCAT Chemistry chapter 9 test free?
Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.
How is the chapter test marked?
The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.
