Free Standard Hydrogen Electrode MCQs with Answers

1. The electrode potential of the standard hydrogen electrode is assigned a value of

• 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 quoted relative to it. The value 0.76 volts is the standard potential of the zinc electrode measured against it, which is why it appears as a distractor. The conditions specified are 1 molar hydrogen ions, 1 atmosphere of hydrogen gas and 298 K.

2. The standard hydrogen electrode consists of hydrogen gas at 1 atmosphere bubbled over

• 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 coating provides a large surface that catalyses the equilibrium between hydrogen gas and hydrogen ions. The solution must be exactly 1 molar in hydrogen ions and the temperature 298 K for the potential to be standard. Any reactive metal would corrode and destroy the reference.

3. A metal with a large negative standard electrode potential is

• 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 acts as a powerful reducing agent, as lithium and potassium do. Metals at the positive end of the series, such as gold and silver, hold their electrons tightly and are unreactive. The electrochemical series is simply the reactivity series expressed in volts.

4. The standard electrode potential of a half cell is measured under conditions of

• 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 K, so that values from different laboratories can be compared. Departing from these conditions changes the measured potential, which the Nernst equation quantifies. Note that 298 K is 25 degrees Celsius, not the 273 K of standard temperature for gases.

5. The order of ease of reduction of H+1, Cu+2 and Ag+1:

• A. H+1 > Cu+2 > Ag+
• B. H+1 > Ag+ > Cu+2
• C. Ag+ > Cu+2 > H+1
• D. H+1 > Cu+2 > Ag+

Explanation: The more positive the standard electrode potential, the more readily the ion accepts electrons, and the values are plus 0.80 V for silver, plus 0.34 V for copper and zero for hydrogen by definition. Silver is therefore reduced most easily and hydrogen least, which is also why copper and silver do not displace hydrogen from dilute acids. Note that options (a) and (d) were printed identically in the original paper.