The mass of silver (Molar mass of Ag: 108 gmol⁻¹ ) displaced by a quantity of electricity which displaces 5600 mL of O₂ at S.T.P. will be ______ g.

Solution

Chemistry ma’am · 4 steps

Same charge passes through both, so count the electrons from the oxygen and hand them to silver.

1. Moles of oxygen. At STP one mole of gas occupies 22.4 L. So 5600 mL = 5.6 L of O₂ is 5.6/22.4 = 0.25 mol.

   2H₂O → O₂ + 4H⁺ + 4e⁻

2. Electrons passed. Each O₂ releases 4 electrons. So 0.25 × 4 = 1 mol of electrons flowed, which is exactly 1 F.
3. Silver deposited. Ag⁺ + e⁻ → Ag needs one electron per atom, so 1 F deposits 1 mol of silver, that is 1 × 108 = 108 g.
4. So. The mass of silver displaced is 108 g.

The common slip: 54. Taking 2 electrons per O₂ instead of 4 gives only 0.5 F and 54 g of silver. Each oxygen atom goes from -2 to 0, so one O₂ needs 4.

The idea to keep. When one charge passes through two processes, convert the first product to moles of electrons, then divide by the electrons each atom of the second product needs. For O₂, always count 4.

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