Question

What is the pH of 0.01 M solution of HCl?
(a) 1
(b) 10
(c) 5
(d) 2

Answer 1

Hint: pH is a scale which is used to determine the acidity or basicity of a compound. It is expressed as a negative log of proton concentration. A higher value of pH more than 7 indicates basic solution while a lower value of pH less than 7 indicates solution is acidic.

Complete step by step answer:
Let us see the dissociation of HCl in an aqueous solution.
\[{{H}^{+}}+C{{l}^{-}}\to HCl\]
\[H\to {{H}^{+}}+{{e}^{-}}\]
\[Cl+{{e}^{-}}\to C{{l}^{-}}\]
HCl dissociates as proton (\[{{H}^{+}}\]) and chloride anion (\[C{{l}^{-}}\]) in an aqueous solution.
From the above reaction (i), we can see that 1 mole of \[{{H}^{+}}\]reacts with 1 mole of \[C{{l}^{-}}\]to give 1 mole of Hydrochloric acid – HCl.
Therefore, 0.01 M solution of HCl will produce 0.01 M of \[{{H}^{+}}\].
pH is defined as the negative log of the hydrogen ion concentration. Mathematically, it is expressed as –
pH = - log [\[{{H}^{+}}\]]
Putting the value of hydrogen ion concentration, we get –
pH = - log [0.01]
pH = - log (\[{{10}^{-2}}\])
pH = 2 log 10
Since, log 10 = 1,
Therefore, pH = 2
Hence, the answer is – option (d) – the pH of 0.01 M solution of HCl is 2.

Additional Information:
Like pH, we can also calculate the value of pOH. It is the concentration of hydroxyl ions present in an aqueous solution. It is related to pH as
=>pOH = 14 – pH.

Note: “pH is a scale used to specify the acidity or basicity of an aqueous solution. Lower pH values correspond to solutions which are more acidic in nature, while higher values correspond to solutions which are more basic or alkaline”. A pH value equal to 7 indicated a neutral compound.