JEE Main 2022 · 27 June · evening · Numerical answer · +4 / −0
pH value of 0.001 M NaOH solution is ____________.
Answer and solution
Answer 11
Solution
Chemistry ma’am · 3 steps
NaOH is a strong base, so find pOH from the hydroxide concentration first, then subtract from 14.
- Full dissociation. NaOH is a strong base and dissociates completely: NaOH → Na⁺ + OH⁻. So [OH⁻] = 0.001 M = 10⁻³ M.
- Find pOH. pOH = -log[OH⁻] = -log(10⁻³) = 3.
pH + pOH = 14 (at 25°C)
- So. pH = 14 - 3 = 11.
The common slip: 3. Taking -log(0.001) as the pH directly gives 3, which is the pOH. A basic solution must have pH above 7.
The idea to keep. For a base, the log of the concentration gives pOH, not pH. Always finish with pH = 14 - pOH.
Answer from the NTA final answer key. Solution by PrepWiser.