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Lesson: Electroplating and Coulometry

In this lesson, we will learn how to calculate the molar mass of a material from the electroplating current and rate of deposition.

Worksheet • 5 Questions

Q1:

An electrode is electroplated with 1.296 g of an elemental metal over a period of 3.00 hours. A constant current of 195 mA is maintained during this process. Given that an ion of the metal has a 2+ charge, determine the relative atomic mass of the metal deposited on the electrode.

Q2:

An electrolytic cell is constructed from a copper plate anode and a copper mesh cathode immersed in an acidic aqueous solution of copper(II) sulfate. A constant current of 140 mA passes through the cell for 60.0 minutes. Calculate the increase in mass of the copper cathode.

Q3:

After the electrolysis of an aqueous solution of copper(II) sulfate, a deposit of 0.50 g of copper is left on the cathode.

How many moles of electrons are required to generate this deposit of copper?

  • A 1 . 6 × 1 0 − 2 mol
  • B 1 . 7 × 1 0 − 2 mol
  • C 7 . 9 × 1 0 − 3 mol
  • D 3 . 4 × 1 0 − 2 mol
  • E 9 . 0 × 1 0 − 3 mol

Taking the charge of an electron to be 1 . 6 × 1 0 − 1 9 C, what is the total charge required to produce this deposit?

  • A 2 . 5 × 1 0 − 2 1 C
  • B 2 . 7 × 1 0 − 2 1 C
  • C 1 . 3 × 1 0 − 2 1 C
  • D 5 . 4 × 1 0 − 2 1 C
  • E 1 . 4 × 1 0 − 2 1 C

Q4:

The atomic mass of an aqueous metal ion is estimated by electroplating the metal onto a cathode and comparing the current in the electrolytic cell to the mass of metal deposited. A student guesses that the oxidation state of the metal ion is +2. In reality, the oxidation state of the metal ion is +4. How does the calculated atomic mass compare to the true atomic mass?

  • AThe calculated mass is half the true mass.
  • BThe calculated mass is four times the true mass.
  • CThe calculated mass is one-quarter of the true mass.
  • DThe calculated mass is double the true mass.
  • EThe calculated mass is equal to the true mass.

Q5:

The atomic mass of an aqueous metal ion can be estimated by electroplating the metal onto a cathode and comparing the current in the electrolytic cell to the mass of metal deposited. Which of the following effects could not cause the atomic mass of the metal to be underestimated?

  • AThe concentration of the dissolved metal is higher than expected.
  • BThe cathode material has more negative electrode potential than the dissolved metal.
  • CHydrogen gas is also produced at the cathode of the cell.
  • DThe oxidation state of the dissolved metal is higher than expected.
  • ESome of the deposited metal breaks away from the cathode.
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