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Last updated date: 20th Jun 2024
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Hint:The pH is defined as the potential of hydrogen which tells us about the concentration of hydrogen ions in the aqueous solution. It tells us whether the given solution is acidic or basic. The pH scale ranges from 0-14, pH less than 7 specifies acidity and pH greater than 7 specifies basicity, pH of 7 comes under neutral i.e. at this pH value there are equal no. of hydrogen and hydroxyl ions.
Formula Used: $pH=-log {{H} ^ {+}} $

Complete step by step answer:
Given concentration of hydrochloric acid is 0.1M. To find its pH value we will use the formula-$pH=-log {{H} ^ {+}} $
 $\Rightarrow$ $pH=-\log (0.1) $
  $\Rightarrow$ $pH=-\log ({{10} ^ {-1}} $
 $\Rightarrow$ $pH=-(-1)\log 10$
 $\Rightarrow$ $pH=+1\log 10$
 $\Rightarrow$ $pH=+1$ (log10 = 1)

So, the pH of 0.1M HCl is +1 which is quite less than 7 which indicates that HCl is a strong acid.

Additional Information: Dissociation constant is a term which determines the strength of an acid. It determines the dissociation of an acid in the aqueous solution. The acid with high dissociation constant means that it will dissociate highly into its ions in the aqueous solution. The pH value for a strong acid will be less than that for a weak acid which indicates that as the pH value approaches 7 the strength of acid keeps on decreasing. After crossing the value 7 the acidic character is lost and basicity comes into action. The pH scale is logarithmic due to which each whole pH value below 7 is ten times more acidic than the next higher value.
The pH value can be measured using litmus paper, electrochemical measuring systems and colorimeters. The pH value is significant as it reflects the chemical conditions of the solution. The human body also has different levels of pH for different body parts as our blood is slightly alkaline or basic with pH value between 7.35 and 7.45 whereas our stomach is quite acidic so that it can break down food for digestion.
The pH value of 14 corresponds to an aqueous solution of a strong base of molarity 1 and pH value of 0 corresponds to an aqueous solution of a strong acid or molarity 1. Higher concentrations of acid and base can result in pH<0 and pH>14 respectively. But generally pH scale ranges from 0-14 only.

The negative value of pH can be obtained if molarity of hydrogen ions is greater than 1. Remember that pH scale is logarithmic scale which means that the change in two consecutive values is not by a factor of 1. A solution of very strong acid will result in pH value 0 and similarly a solution of a very strong base will result in pH value 14.