Which of the following solutions will have pH close to 1.0? — Ionic Equilibrium Chemistry Question

💡 Solution & Explanation

(A) Equal moles of strong acid and strong base result in a neutral solution, pH = 7. (B) Moles of HCl = $5.5\text{ mmol}$, Moles of NaOH = $4.5\text{ mmol}$. Excess HCl = $1.0\text{ mmol}$ in $100\text{ ml}$, so $[\text{H}^+] = 0.01\text{ M}$ and pH = 2.0. (C) Excess base leads to an alkaline solution (pH > 7). (D) Moles of HCl = $75 \times 0.2 = 15\text{ mmol}$, Moles of NaOH = $25 \times 0.2 = 5\text{ mmol}$. Excess HCl = $10\text{ mmol}$ in $100\text{ ml}$, so $[\text{H}^+] = 0.1\text{ M}$ and pH = 1.0. Therefore, correct answer is D.