Payal has to arrange the following in DECREASING order of hydroxide ion concentration. wine (pH 4.0), milk of magnesia (pH 10.5), blood (pH 7.4) Which of the following arrangements is correct?

Options

A. wine -`gt` milk of magnesia -`gt` blood
B. blood -`gt` milk of magnesia -`gt` wine
C. milk of magnesia -`gt` blood -`gt` wine
D. wine -`gt` blood -`gt` milk of magnesia

Answer

To arrange the given substances in decreasing order of hydroxide ion concentration, we first need to understand the relationship between pH and hydroxide ion concentration. The pH scale ranges from 0 to 14, where:

- pH < 7 indicates an acidic solution (higher concentration of H⁺ ions and lower concentration of OH⁻ ions).
- pH = 7 indicates a neutral solution (equal concentration of H⁺ and OH⁻ ions).
- pH > 7 indicates a basic solution (lower concentration of H⁺ ions and higher concentration of OH⁻ ions).

### Step-by-Step Solution:

1. **Identify the pH values:**
- Wine: pH = 4.0
- Milk of Magnesia: pH = 10.5
- Blood: pH = 7.4

2. **Classify the solutions based on pH:**
- Wine (pH 4.0) is acidic.
- Blood (pH 7.4) is slightly basic.
- Milk of Magnesia (pH 10.5) is basic.

3. **Determine the hydroxide ion concentration:**
- The hydroxide ion concentration can be calculated using the formula:
\[ [OH⁻] = 10^{-(14 - \text{pH})} \]
- For Wine (pH 4.0):
\[ [OH⁻] = 10^{-(14 - 4)} = 10^{-10} \text{ M} \]
- For Blood (pH 7.4):
\[ [OH⁻] = 10^{-(14 - 7.4)} = 10^{-6.6} \text{ M} \approx 2.51 \times 10^{-7} \text{ M} \]
- For Milk of Magnesia (pH 10.5):
\[ [OH⁻] = 10^{-(14 - 10.5)} = 10^{-3.5} \text{ M} \approx 3.16 \times 10^{-4} \text{ M} \]

4. **Arrange in decreasing order of hydroxide ion concentration:**
- Milk of Magnesia (pH 10.5) has the highest hydroxide ion concentration.
- Blood (pH 7.4) has a moderate hydroxide ion concentration.
- Wine (pH 4.0) has the lowest hydroxide ion concentration.

### Final Arrangement:
1. Milk of Magnesia (pH 10.5)
2. Blood (pH 7.4)
3. Wine (pH 4.0)

### Correct Answer:
**Milk of Magnesia > Blood > Wine**

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