Free Electrochemistry MCQs with Answers

• A. loss of electrons and an increase in oxidation number
• B. gain of electrons and a decrease in oxidation number
• C. gain of hydrogen only
• D. loss of oxygen only

Explanation: The modern definition is in terms of electrons, so oxidation is loss and reduction is gain, remembered as OIL RIG.

• A. plus 2
• B. plus 6
• C. minus 2
• D. plus 4

Explanation: Hydrogen contributes plus 1 each and oxygen minus 2 each, so 2 plus x minus 8 equals zero and x is plus 6.

• A. the sulphate ion
• B. copper ions
• C. zinc
• D. copper metal

Explanation: Zinc goes from an oxidation number of zero as the metal to plus 2 in the sulphate, so it has lost electrons and is oxidised, which also…

• A. loses electrons and is itself oxidised
• B. gains electrons and is itself reduced
• C. neither gains nor loses electrons
• D. always contains oxygen

Explanation: An oxidising agent oxidises something else by taking its electrons, so it is itself reduced in the process, and the same reasoning in…

• A. minus 2
• B. zero
• C. minus 1
• D. plus 2

Explanation: Hydrogen is plus 1, so the two oxygens must total minus 2 between them, giving minus 1 each, which is the exception to the usual rule of…

• A. a neutralisation reaction
• B. a displacement reaction
• C. a precipitation reaction
• D. a disproportionation reaction

Explanation: In disproportionation one species with an intermediate oxidation state changes into two products, one at a higher and one at a lower…

• A. the number of atoms of oxygen is the same in both
• B. the number of electrons lost equals the number gained
• C. the charges on both sides are zero
• D. the coefficients are all whole numbers greater than one

Explanation: Electrons cannot appear in the final equation, so the two half equations are scaled until the electrons cancel exactly on addition, which…

• A. hydroxide ions
• B. oxygen gas
• C. water molecules to the side deficient in oxygen
• D. hydrogen gas

Explanation: Water supplies the missing oxygen, and hydrogen ions are then added to the opposite side to balance the hydrogen introduced, which is…

• A. 0.00 volts by convention
• B. 1.00 volt
• C. minus 1.00 volt
• D. 0.76 volts

Explanation: No single electrode potential can be measured in isolation, so the hydrogen electrode is defined as zero and every other potential is…

• A. a zinc rod in zinc sulphate solution
• B. platinised platinum foil dipping in 1 molar hydrogen ion solution
• C. a copper rod in copper sulphate solution
• D. a carbon rod in pure water

Explanation: Platinum is used because it is chemically inert and does not itself take part in the reaction, while the finely divided platinum black…

• A. cathode
• B. salt bridge
• C. anode
• D. voltmeter

Explanation: The anode is by definition the electrode at which oxidation occurs and reduction occurs at the cathode, and this holds for both galvanic…

• A. allow electrons to pass between the two solutions
• B. complete the circuit by allowing ions to migrate and keeping both solutions electrically neutral
• C. prevent the cell from producing any current
• D. act as a catalyst for the reaction

Explanation: As the cell runs, positive charge builds up in one half cell and negative charge in the other, which would stop the reaction almost…

• A. a strong reducing agent that is easily oxidised
• B. a strong oxidising agent
• C. chemically unreactive
• D. unable to form ions

Explanation: A large negative value means the metal releases electrons readily and prefers to exist as its ion, so it is easily oxidised and therefore…

• A. plus 3
• B. plus 12
• C. plus 6
• D. plus 7

Explanation: Seven oxygens contribute minus 14, and the overall charge is minus 2, so the two chromium atoms must total plus 12, giving plus 6 each.

• A. lose electrons there
• B. gain electrons and are reduced there
• C. are attracted to the anode
• D. react with chlorine there

Explanation: Positive sodium ions migrate to the negative cathode, each accepting one electron to become a sodium atom, which is reduction.

• A. a reducing agent because it gains electrons
• B. neither an oxidising nor a reducing agent
• C. a catalyst
• D. an oxidising agent because it accepts electrons from sodium

Explanation: Each chlorine atom accepts one electron and falls from zero to minus 1, so chlorine is reduced and is therefore the oxidising agent, while…

• A. 1 molar solution, 298 K and 1 atmosphere pressure
• B. any concentration at 273 K
• C. 0.1 molar solution at 373 K
• D. pure water at room temperature

Explanation: Standard conditions fix the concentration of every solution at 1 molar, the pressure of any gas at 1 atmosphere and the temperature at 298…

• A. Zn + 2HCl gives ZnCl2 + H2
• B. 2H2 + O2 gives 2H2O
• C. NaOH + HCl gives NaCl + H2O
• D. 2Mg + O2 gives 2MgO

Explanation: In neutralisation no element changes its oxidation number, since hydrogen stays at plus 1, oxygen at minus 2 and both sodium and chlorine…

• A. displace a metal lower in the series from its salt solution
• B. be displaced by a metal lower in the series
• C. never react with acids
• D. always be a poor conductor

Explanation: A more reactive metal gives up electrons more readily, so it reduces the ions of a less reactive metal and takes their place in solution…

• A. plus 1
• B. equal to its group number
• C. minus 1
• D. zero

Explanation: An uncombined element has not gained or lost any electrons, so its oxidation number is zero, and this holds for atoms such as helium and…