Number of equivalents of HCl present in 100 mL of its solution whose pH is 4:

Options

A. `10^(-4)`
B. `10^(-3)`
C. `10^(-2)`
D. `10^(-5)`

Answer

To find the number of equivalents of HCl present in 100 mL of its solution with a pH of 4, we can follow these steps:

### Step 1: Understand the relationship between pH and hydrogen ion concentration.
The pH of a solution is defined as:
\[ \text{pH} = -\log[H^+] \]
Given that the pH is 4, we can find the concentration of hydrogen ions \([H^+]\).

### Step 2: Calculate the concentration of hydrogen ions.
Using the pH value:
\[ 4 = -\log[H^+] \]
To find \([H^+]\), we rewrite the equation:
\[ [H^+] = 10^{-4} \text{ M} \]

### Step 3: Convert the volume from mL to L.
The volume of the solution is given as 100 mL. We need to convert this to liters:
\[ 100 \text{ mL} = 0.1 \text{ L} \]

### Step 4: Calculate the number of moles of hydrogen ions.
Using the concentration and volume, we can find the number of moles of \([H^+]\):
\[ \text{Number of moles} = \text{Concentration} \times \text{Volume} = 10^{-4} \text{ mol/L} \times 0.1 \text{ L} = 10^{-5} \text{ moles} \]

### Step 5: Determine the n-factor for HCl.
For HCl, which is a strong acid, it dissociates completely in solution to give one hydrogen ion per molecule. Therefore, the n-factor (valency factor) for HCl is 1.

### Step 6: Calculate the number of equivalents.
The number of equivalents can be calculated using the formula:
\[ \text{Number of equivalents} = \text{Number of moles} \times \text{n-factor} \]
Substituting the values we have:
\[ \text{Number of equivalents} = 10^{-5} \text{ moles} \times 1 = 10^{-5} \text{ equivalents} \]

### Final Answer:
The number of equivalents of HCl present in 100 mL of its solution whose pH is 4 is \(10^{-5}\).

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