Which statement is not true?

Options

A. `pH of 1xx10^(-8)M HCl` is 8
B. 96500 coulomb deposits 1 g equivalent of copper
C. Conjugate base of `H_(2)PO_(4)^(-)` is `HPO_(4)^(2-)`
D. pH + pOH = 14 for all aqueous solution

Explanation

To determine which statement is not true, we will analyze each statement one by one.

### Step 1: Analyze Statement 1
**Statement:** The pH of 1 × 10⁻⁸ molar HCl is 8.

- **Explanation:**
- HCl is a strong acid and dissociates completely in solution.
- The concentration of H⁺ ions from the HCl is 1 × 10⁻⁸ M.
- However, in very dilute solutions, we must also consider the contribution of H⁺ ions from water, which is 1 × 10⁻⁷ M.
- Therefore, the total concentration of H⁺ ions in the solution is:
\[ [H^+] = 1 \times 10^{-8} + 1 \times 10^{-7} = 1.1 \times 10^{-7} \text{ M} \]
- Now, we calculate the pH:
\[ pH = -\log(1.1 \times 10^{-7}) \approx 6.96 \]
- Since the pH is approximately 6.96, the statement claiming the pH is 8 is **not true**.

### Step 2: Analyze Statement 2
**Statement:** 96500 coulombs deposit 1 gram equivalent of copper.

- **Explanation:**
- According to Faraday's laws of electrolysis, 1 Faraday (96500 coulombs) will deposit 1 gram equivalent of a substance.
- For copper, which has a valency of 2, 1 gram equivalent corresponds to 63.5 grams of copper.
- Therefore, this statement is **true**.

### Step 3: Analyze Statement 3
**Statement:** The conjugate base of H₂PO₄⁻ is HPO₄²⁻.

- **Explanation:**
- The conjugate base is formed by removing one H⁺ ion from the acid.
- Starting with H₂PO₄⁻, if we remove one H⁺, we get HPO₄²⁻.
- Thus, this statement is **true**.

### Step 4: Analyze Statement 4
**Statement:** pH + pOH = 14 for all aqueous solutions.

- **Explanation:**
- The relationship pH + pOH = 14 holds true at 25°C for pure water and dilute aqueous solutions.
- This is derived from the ion product of water (K_w) at 25°C, where K_w = 1 × 10⁻¹⁴.
- Therefore, this statement is **true**.

### Conclusion:
The statement that is **not true** is **Statement 1**: "The pH of 1 × 10⁻⁸ molar HCl is 8."

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