Question

What is the concentration of \( \text{H}^+ \) ions if the pH is 2.7?

• A. \( 2.00 \times 10^{-3} \, \text{M} \)
• B. \( 1.99 \times 10^{-3} \, \text{M} \)
• C. \( 1.80 \times 10^{-3} \, \text{M} \)
• D. None of the above

Hint:

To calculate \( [\text{H}^+] \) from pH, use the formula \( [\text{H}^+] = 10^{-\text{pH}} \). Ensure the pH value is correctly substituted.

Answer 1

The Correct Option is B

The pH of a solution is related to the concentration of hydrogen ions (\( \text{H}^+ \)) by the equation: \[ \text{pH} = -\log [\text{H}^+] \] Given that the pH is 2.7, we can rearrange the equation to solve for \( [\text{H}^+] \): \[ [\text{H}^+] = 10^{-\text{pH}} = 10^{-2.7} \] Calculating \( 10^{-2.7} \): \[ 10^{-2.7} \approx 2.00 \times 10^{-3} \, \text{M} \] However, considering significant figures and more precise calculation: \[ 10^{-2.7} \approx 1.99 \times 10^{-3} \, \text{M} \] Thus, the concentration of hydrogen ions is approximately \( 1.99 \times 10^{-3} \, \text{M} \).