Electrolysis of 600 mL aqueous solution of NaCl for 5 min changes the pH of the solution to 12 .
The current in Amperes used for the given electrolysis is ___________ . (Nearest integer).

Solution

Chemistry ma’am · 3 steps

The pH tells you how much hydroxide was made, and each hydroxide ion cost exactly one electron.

1. Where OH⁻ comes from. At the cathode water is reduced: 2H₂O + 2e⁻ → H₂ + 2OH⁻. Each electron that passes produces one OH⁻ ion. Na⁺ stays as a spectator, so the solution becomes NaOH.
2. Moles of OH⁻. pH 12 means pOH 2, so [OH⁻] = 10⁻² mol L⁻¹. In 0.6 L that is 0.01 × 0.6 = 6 × 10⁻³ mol of OH⁻, which also equals the moles of electrons.

   I = nF/t = (6 × 10⁻³ × 96500)/300 = 579/300 = 1.93 A

3. So. With t = 5 × 60 = 300 s, the current is 1.93 A, which rounds to 2.

The common slip: 116. Putting t = 5 instead of 300 s gives 579/5 ≈ 116 A. Always convert minutes to seconds before dividing.

The idea to keep. In NaCl electrolysis, moles of OH⁻ formed equal moles of electrons passed. Get them from the final pH and volume, then use Q = nF with time in seconds.

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