Understanding pH and Hydrogen Ion Concentration

The pH scale is a logarithmic scale used to measure the acidity or alkalinity of a solution. It ranges from 0 to 14, where pH 7 is considered neutral, pH less than 7 indicates acidity, and pH greater than 7 indicates alkalinity. pH is defined as the negative logarithm (base 10) of the concentration of hydrogen ions (H+) in a solution.

Calculating pH from Hydrogen Ion Concentration

To calculate the pH from the hydrogen ion concentration, we can use the formula: pH = -log[H+]. In this case, the hydrogen ion concentration is given as 10000 nM (nanomolar).

Conversion of Concentration Units

Before calculating the pH, we need to convert the concentration from nanomolar (nM) to molar (M) as the pH calculation requires the concentration in molar units.

1 nanomolar (nM) = 1 × 10^-9 moles per liter (M)

Therefore, the hydrogen ion concentration of 10000 nM can be converted to 1 × 10^-5 M.

Calculating pH

Now, we can calculate the pH using the formula: pH = -log[H+].

Taking the negative logarithm of 1 × 10^-5 M, we get:

pH = -log(1 × 10^-5) = -(-5) = 5

Therefore, the pH of the solution with a hydrogen ion concentration of 10000 nM is 5.

Explanation of the Correct Answer

The correct answer is given as between 4.5 and 5.5. This range is appropriate because the pH scale is logarithmic, meaning that each unit represents a tenfold difference in acidity or alkalinity. Since the solution has a pH of 5, it is slightly acidic. The range of 4.5 to 5.5 indicates that the pH is closer to 5 than to 4.5 or 5.5. Hence, the correct answer falls within this range.