The pH of millimolar HCl is

Options

A. 1
B. 2
C. 3
D. 4

Explanation

To find the pH of a millimolar HCl solution, follow these steps:

### Step 1: Understand the concentration
- The term "millimolar" refers to a concentration of 1 millimole per liter, which is equivalent to \(10^{-3}\) moles per liter (M). Therefore, if we have a millimolar HCl solution, its concentration can be expressed as:
\[ [\text{HCl}] = 1 \, \text{mM} = 10^{-3} \, \text{M} \]

### Step 2: Recognize that HCl is a strong acid
- HCl is a strong acid, which means it completely ionizes in solution. The ionization can be represented as:
\[ \text{HCl} \rightarrow \text{H}^+ + \text{Cl}^- \]
- Since HCl completely dissociates, the concentration of hydrogen ions \([\text{H}^+]\) in the solution will be equal to the concentration of HCl:
\[ [\text{H}^+] = 10^{-3} \, \text{M} \]

### Step 3: Calculate the pH
- The pH of a solution is calculated using the formula:
\[ \text{pH} = -\log[\text{H}^+] \]
- Substituting the concentration of hydrogen ions into the formula:
\[ \text{pH} = -\log(10^{-3}) \]
- Using the properties of logarithms, this simplifies to:
\[ \text{pH} = 3 \]

### Conclusion
- Therefore, the pH of a millimolar HCl solution is:
\[ \text{pH} = 3 \]

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