135 g of water is electrolyzed during an experiment. If the efficiency of current is 75% then select the correct statement. (1) 168 L of O2(g) will be evolved at anode at STP (2) 84 L of H2(g) will be evolved at cathode at STP (3) 15 F electricity will be consumed (4) 20 F electricity will be consumed?

Question

135 g of water is electrolyzed during an experiment. If the efficiency of current is 75% then select the correct statement. (1) 168 L of O2(g) will be evolved at anode at STP (2) 84 L of H2(g) will be evolved at cathode at STP (3) 15 F electricity will be consumed (4) 20 F electricity will be consumed​?

Answer

Solution:

Given, 135 g of water is electrolyzed with an efficiency of 75%.

1. Calculation of moles of water electrolyzed

The molar mass of water is 18 g/mol. Therefore, the number of moles of water electrolyzed is given by:

Number of moles = 135 g / 18 g/mol = 7.5 mol

2. Calculation of moles of hydrogen and oxygen evolved

From the balanced chemical equation for the electrolysis of water, we know that 2 moles of hydrogen and 1 mole of oxygen are evolved for every 2 moles of water electrolyzed. Therefore, the number of moles of hydrogen and oxygen evolved are:

Number of moles of H2 = 7.5 mol × 2/2 = 7.5 mol

Number of moles of O2 = 7.5 mol × 1/2 = 3.75 mol

3. Calculation of volume of hydrogen and oxygen evolved at STP

The volume of a gas at STP (Standard Temperature and Pressure) is 22.4 L/mol. Therefore, the volume of hydrogen and oxygen evolved at STP are:

Volume of H2 = 7.5 mol × 22.4 L/mol = 168 L

Volume of O2 = 3.75 mol × 22.4 L/mol = 84 L

4. Calculation of electricity consumed

The Faraday constant is the amount of electric charge carried by one mole of electrons, and its value is 96,485 C/mol. Therefore, the amount of electricity consumed is given by:

Electricity consumed = Number of moles × Faraday constant × Efficiency

Electricity consumed = 7.5 mol × 96,485 C/mol × 0.75 = 546,318.75 C = 15 F

Therefore, the correct statements are:

(1) 168 L of O2(g) will be evolved at anode at STP

(2) 84 L of H2(g) will be evolved at cathode at STP

(3) 15 F electricity will be consumed

Note: The statement (4) 20 F electricity will be consumed is incorrect as the actual value of electricity consumed is 15 F.

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