Question

What is the pH of $ 0.025M $ $ HCl $ solution?

Answer 1

Hint: pH of a solution is the negative logarithm of concentration of $ {H^ + }\; $ ions. pH helps to identify whether a solution is acidic, basic or neutral. In the question molarity of hydrochloric acid is given, use this concentration to find out the pH using the pH formula. The formula for pH is: $ pH = - log[{H^ + }] $ .

Complete Step By Step Answer:
pH is defined as the negative logarithm of $ {H^ + }\; $ ion concentration. It is a measure of how acidic/basic water or any solution is.
The measurement was originally used by the Danish biochemist S.P.L. Sorensen to represent the hydrogen ion concentration, expressed in equivalents per liter, of an aqueous solution. Its formula is given as:
 $ pH = - log[{H^ + }] $
In the question given above we have to determine the pH of $ 0.025M $ of strong acid $ HCl $ . It is known that the hydrochloric acid $ HCl $ is a strong acid as it dissociates completely in water. And this ionization is hardly affected by the presence/absence of other solutes present in the same solution. Therefore dissociation occurs like,
 $ HCl \to {H^ + } + C{l^ - } $
So, the concentration of $ HCl $ is given as $ 0.025M $ .
Thus, we can write it as $ \left[ {{H^ + }} \right]{\text{ }} = {\text{ }}\left[ {HCl} \right]{\text{ }} = {\text{ }}0.025M $
Now that we know the value of $ {H^ + }\; $ we can substitute this value in the formula to find out the pH of the Hydrochloric acid.
Thus, $ pH = - log[{H^ + }] $
 $ \Rightarrow pH = - log[0.025] $
 $ \Rightarrow pH = - ( - 1.60206) $
 $ \Rightarrow pH = + 1.60206 $
Therefore the value of pH is $ + 1.60206 $ .

Note:
pH of solutions can be physically found out by several methods like using pH meter, pH paper, and litmus paper etc. pH has several applications. The pH of strong acid usually lies between $ 0 - 2 $ and of strong base it lies between $ 10 - 14 $ .