(a) Distinguish between a conductor and an electrolyte (b)(i) State Faraday's first law of electrolysis (ii) Describe how you would investigate Faraday's la...

Answer Details

(a) Conductor vs electrolyte

A conductor is a substance that allows electricity to pass through it without undergoing any chemical change; it conducts by the movement of free electrons (for example, a metal). An electrolyte is a substance which, in the molten state or in aqueous solution, conducts electricity and is chemically decomposed by it; it conducts by the movement of ions.

(b)(i) Faraday's first law

The mass of a substance liberated or deposited at an electrode during electrolysis is directly proportional to the quantity of electricity (charge) passed through the electrolyte.

(ii) Investigation

• Weigh a clean, dry copper cathode and record its mass.
• Set up an electrolytic cell containing copper(II) tetraoxosulphate(VI) solution with two copper electrodes, connected in series with an ammeter, a rheostat and a switch.
• Pass a steady current I (read on the ammeter) for a measured time t (with a stopwatch); the charge is Q = It.
• Remove, wash, dry and re-weigh the cathode to find the mass of copper deposited.
• Repeat for different values of Q, then plot a graph of mass deposited against Q. A straight line through the origin confirms that mass is proportional to charge.

(c) Relative atomic mass

\[Q = It = 0.45 \times (25 \times 60) = 675\,C\]

For a divalent metal, M²⁺ + 2e^- → M, so 2 × 96500 C deposit 1 mole of metal.

\[\text{moles of metal} = \frac{675}{2 \times 96500} = 3.497 \times 10^{-3}\,mol\]

\[\text{RAM} = \frac{0.222}{3.497 \times 10^{-3}} \approx 63.5\]

The relative atomic mass of the metal is about 63.5 (the metal is copper).

(d) Two applications of electrolysis

• Electroplating of metals (for example, coating with silver, chromium or nickel).
• Purification (refining) of metals such as copper; also the extraction of reactive metals such as aluminium and sodium.