One Faraday of electricity liberates x × 10⁻¹ gram atom of copper from copper sulphate. x is ________.

Solution

Chemistry ma’am · 4 steps

Each copper ion needs two electrons, so one mole of electrons can only make half a mole of copper.

1. What one Faraday is. One Faraday is the charge on one mole of electrons, about 96500 C. So the question is asking how much copper one mole of electrons can deposit.
2. Cathode reaction. In copper sulphate solution, copper is present as Cu²⁺. Each ion needs two electrons to become a copper atom.

   Cu²⁺ + 2e⁻ → Cu

3. Use the ratio. 2 mol of electrons give 1 mol of Cu, so 1 mol of electrons gives 1/2 = 0.5 mol of Cu. A gram atom is the same as one mole of atoms, so this is 0.5 gram atom, or about 31.75 g.
4. So. 0.5 = 5 × 10⁻¹ gram atom, so x = 5.

The common slip: 10. Taking one Faraday to deposit one gram atom of copper ignores the 2+ charge on the ion. It gives 1 gram atom, so x = 10 instead of 5.

The idea to keep. Moles deposited = Faradays passed divided by the charge on the ion. Always write the electrode reaction first, so you can see how many electrons each atom needs.

Answer from the NTA final answer key. Solution by PrepWiser.