Question

The pH of 0.1M ammonium hydroxide is.
A. 14
B. \[ < 13\]
C. \[ > 13\]
D. \[ < 7\]

Answer 1

Hint: pH is a way of measuring the acidity or basicity of a given compound. It represents the number of \[{H^ + }\] ions present in the given compound. The acidic character of a compound is dependent on the concentration of the \[{H^ + }\] ions present in it.

Formula used: \[pOH = - \log \left[ {O{H^ - }} \right]\]

Complete step by step answer:
The higher the number of \[{H^ + }\] ions present, the greater is the acidic character of that compound. Mathematically, it is equivalent to the negative logarithmic value of the concentration of the \[{H^ + }\] ions in a compound. It can be represented as:
 \[pH = - log[{H^ + }]\]
in case of concentration of \[O{H^ - }\] , \[pOH = - \log \left[ {O{H^ - }} \right]\] .
pH is measured on a scale of 1 to 14, where 1 means the most acidic while 14 means most basic. Chemically neutral substances lie at the center of this scale, i.e. at 7. This is because the acidic character of a neutral substance is balanced by its basic character. To put it in simpler terms, let us understand another small concept: the basic character of a substance is determined by the concentration of \[O{H^ - }\] ions in the compound and is put in perspective by a measure known as the pOH scale.
There is a relation between pH and pOH, which is, \[pH\,\, + pOH = 14\]
Now, moving back to the question, ammonium hydroxide is a weak base.
Now, for 0.1M ammonium hydroxide, the pOH is,
 \[
  pOH = - \log \left[ {O{H^ - }} \right] \\
  pOH = - \log 0.1 \\
  pOH = \log 10 \\
  pOH = 1 \\
 \]
But as ammonium hydroxide is a weak base complete dissociation will not ben taken. So the pH of this solution will be almost 7.
Therefore, the correct answer is, B.

Note:In neutral substances, the concentration of \[O{H^ - }\] and \[{H^ + }\] is equivalent and they cancel each other out to give the neutral characteristic. we know that water is a neutral substance and hence its pH is 7. And as per the explanation above, the number of \[{H^ + }\] ions is equal to the number of \[O{H^ - }\] ions and hence they cancel out their acidic and basic properties to give water its neutral nature.