4 gram of NaOH is added in water to form 500 mL solution at 298 K . What is pH of solution? (Molar mass of NaOH =40 ~g ~mol ⁻¹ )

Step-by-step solution

Finding the pH of a sodium hydroxide solution The solution contains 4 g of NaOH dissolved in 500 mL. The molar mass of NaOH is 40 g mol ⁻¹ , giving 4 40 = 0.1 mol. For a 0.5 L solution, the molarity is 0.1 0.5 = 0.2 M. As NaOH is a strong base that dissociates completely, [ OH ⁻] = 0.2 M. The pOH is calculated as - ₁₀(0.2) = - ₁₀(2 10⁻¹) = -( ₁₀2 + ₁₀10⁻¹) = -(0.3010 - 1) = 0.6990 . At 298 K, pH + pOH = 14, so pH = 14 - 0.6990 = 13.3010. This corresponds to option D .