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Current Question (ID: 8476)

Question:

$\text{The pH of neutral water at } 25^\circ\text{C} \text{ is } 7.0. \text{ As the temperature increases, ionisation of water increases. However, the concentration of } \text{H}^+ \text{ ions and } \text{OH}^- \text{ ions is equal. What will be the pH of pure water at } 60^\circ\text{C} \text{?}$

Options:

1. $\text{Equal to } 7.0$
2. $\text{Greater than } 7.0$
3. $\text{Less than } 7.0$
4. $\text{Equal to zero}$

Solution:

$\textbf{HINT: } \text{With increase in temperature } K_w \text{ increases.}$ $\text{The pH of neutral water at } 25^\circ\text{C} \text{ is } 7.0.$ $\text{At } 25^\circ\text{C}, [\text{H}^+] = [\text{OH}^-] = 10^{-7}$ $\text{and } K_w = [\text{H}^+][\text{OH}^-] = 10^{-14}$ $\text{On heating, } K_w \text{ increases, i.e., } [\text{H}^+][\text{OH}^-] > 10^{-14}$ $\text{As } [\text{H}^+] = [\text{OH}^-] \text{ or, } [\text{H}^+]^2 \geq 10^{-14}$ $\text{or, } [\text{H}^+] > 10^{-7}\text{M}$ $\therefore \text{pH} < 7$ $\text{With rise in temperature, pH of pure water decreases and it becomes less than } 7 \text{ at } 60^\circ\text{C}.$

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Upload a JSON file containing LaTeX/MathJax formatted question, options, and solution.

Expected JSON Format:

{
  "question": "The mass of carbon present in 0.5 mole of $\\mathrm{K}_4[\\mathrm{Fe(CN)}_6]$ is:",
  "options": [
    {
      "id": 1,
      "text": "1.8 g"
    },
    {
      "id": 2,
      "text": "18 g"
    },
    {
      "id": 3,
      "text": "3.6 g"
    },
    {
      "id": 4,
      "text": "36 g"
    }
  ],
  "solution": "\\begin{align}\n&\\text{Hint: Mole concept}\\\\\n&1 \\text{ mole of } \\mathrm{K}_4[\\mathrm{Fe(CN)}_6] = 6 \\text{ moles of carbon atom}\\\\\n&0.5 \\text{ mole of } \\mathrm{K}_4[\\mathrm{Fe(CN)}_6] = 6 \\times 0.5 \\text{ mol} = 3 \\text{ mol}\\\\\n&1 \\text{ mol of carbon} = 12 \\text{ g}\\\\\n&3 \\text{ mol carbon} = 12 \\times 3 = 36 \\text{ g}\\\\\n&\\text{Hence, 36 g mass of carbon present in 0.5 mole of } \\mathrm{K}_4[\\mathrm{Fe(CN)}_6].\n\\end{align}",
  "correct_answer": 4
}