Chemistry 2008 JAMB Past Questions - Question 25: If a given quantity of electricity liberates 0.65g of Zn²+, what amount of Hg²+ would be liberated by the same quantity of current?

Correct Answer

B

Explanation

1. **Faraday's constant:** The key concept is Faraday's constant, which represents the charge associated with one mole of electrons (approximately 96485 coulombs per mole). This constant tells us that a specific amount of electrical charge transfers a specific amount of electrons, regardless of the metal involved.

2. **Moles of electrons:** When 0.65g of Zn²⁺ is liberated, the corresponding number of electrons transferred can be calculated:

  - Moles of Zn²⁺ = mass of Zn²⁺ / molar mass of Zn²⁺
  - Moles of Zn²⁺ = 0.65g / 65.38 g/mol ≈ 0.0100 mol
  - Since each Zn²⁺ ion gains 2 electrons, moles of electrons transferred = 2 * moles of Zn²⁺ ≈ 0.0200 mol

3. **Moles of Hg²⁺:** Assuming the same amount of electricity liberates Hg²⁺ ions, the moles of Hg²⁺ will be equal to the moles of electrons transferred:

  - Moles of Hg²⁺ = moles of electrons transferred ≈ 0.0200 mol

4. **Mass of Hg²⁺:** Finally, calculate the mass of Hg²⁺ liberated:

  - Mass of Hg²⁺ = moles of Hg²⁺ * molar mass of Hg²⁺
  - Mass of Hg²⁺ ≈ 0.0200 mol * 200.59 g/mol ≈ 4.01 g

Therefore, approximately **4.01g of Hg²+** would be liberated by the same quantity of current that liberates 0.65g of Zn²⁺.