Using the equation pH = -log [H+], a solution with a [H+] = 10-9 M has a pH of which of the following?
A.
5
B.
1
C.
9
D.
10
The correct answer and Explanation is :
To calculate the pH of a solution with a hydrogen ion concentration ([H^+]) of (10^{-9} \, \text{M}), we can use the formula:
[
\text{pH} = -\log [H^+]
]
Substituting the given concentration into the equation:
[
\text{pH} = -\log (10^{-9})
]
Using logarithmic properties, we find:
[
\text{pH} = -(-9) = 9
]
Thus, the pH of the solution is 9, which corresponds to option C.
Explanation
pH is a logarithmic scale used to specify the acidity or basicity of a solution. It is defined as the negative logarithm (base 10) of the hydrogen ion concentration ([H^+]) in moles per liter. A pH of 7 is considered neutral, indicating equal concentrations of hydrogen ions and hydroxide ions in pure water.
When the pH is below 7, the solution is acidic, meaning there are more hydrogen ions than hydroxide ions. Conversely, when the pH is above 7, the solution is basic or alkaline, indicating a higher concentration of hydroxide ions.
In our case, a solution with ([H^+] = 10^{-9} \, \text{M}) has a pH of 9, which places it in the basic range. This is interesting because the solution is only slightly basic. It’s important to note that, at standard temperature (25°C), the pH scale typically ranges from 0 to 14, where values less than 7 indicate acidity and values greater than 7 indicate basicity.
Furthermore, in dilute solutions where ([H^+]) approaches (10^{-7} \, \text{M}), water’s autoionization (the process where water molecules dissociate into hydrogen ions and hydroxide ions) also becomes significant, which can slightly affect the pH calculation. In our case, the calculated pH of 9 accurately reflects the basic nature of the solution.