Electrochemistry Questions and Answers

Answer: A

Water is reduced far more readily than the strongly negative sodium ion, so on most cathodes hydrogen appears instead. The mercury cathode's large hydrogen overvoltage was the exception that made the aqueous route possible.

Answer: B

The specific measurement is on a fixed volume and so follows the ion concentration downward, while the equivalent measurement is on a fixed amount of solute and so follows the dissociation upward. The reason accounts for both halves.

Answer: C

Correct answer: the assertion is false although the reason offered is a true statement in itself

The reason is a true description of what EMF is, but the assertion fails on the method. A low resistance voltmeter draws appreciable current, and drawing current polarises the electrodes and produces a drop across the internal resistance, so the reading falls below the true EMF. The measurement must be made at essentially zero current - by a potentiometer, or by a modern electrometer of very high input impedance.

Answer: D

Nothing has to be seen, so colour and turbidity are no obstacle, and the end point comes from the intersection of two extrapolated lines rather than a single observation. Its sharpness depends on the ionic mobilities involved.

Answer: A

One faraday deposits one gram equivalent of whatever is being discharged, which is the second law exactly. Voltage, area and resistance affect the current and hence the time taken, but not the deposit for a given charge.