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Current Question (ID: 21063)

Question:

$\text{The pH of an ammonium phosphate solution, if the } pK_a \text{ of phosphoric acid and the } pK_b \text{ of ammonium hydroxide are } 5.23 \text{ and } 4.75 \text{ respectively, is:}$

Options:

1. $8$
2. $6$
3. $7$
4. $10$

Solution:

$\text{Hint: Use formula } \text{pH} = 7 + \frac{1}{2} (pK_a - pK_b)$ $\text{Since } (\text{NH}_4)_3\text{PO}_4 \text{ is salt of a weak acid } (\text{H}_3\text{PO}_4) \text{ and weak base } (\text{NH}_4\text{OH}).$ $\text{pH} = 7 + \frac{1}{2} (pK_a - pK_b)$ $= 7 + \frac{1}{2} (5.23 - 4.75)$ $= 7.24 \approx 7$ $\text{Hence, the answer is option third.}$

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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
}