Question

What is the $pH$of $0.05M$ of $HCl$?

Answer 1

Hint: We know that $pH$ of a solution is defined as the concentration of hydrogen ions in the solution. pH scale ranges from value between $0$ to $7$. pH is also defined as the negative of the logarithm base $10$ of the molar concentration of hydrogen ions in the solution

Complete answer:
We know that pH of a solution is defined as the concentration of hydrogen ions in the solution. $pH$ scale ranges from value between $0$ to $7$. Lower the value of pH, higher is the acidity of the solution. Higher the value of pH more basic will be the solution. pH is also defined as the negative of the logarithm base $10$ of the molar concentration of hydrogen ions in the solution. For bases, we can calculate $pOH$, which is defined as the negative of the logarithm base $10$ of the molar concentration of $O{H^ - }$ ions in the solution. For pH, we can therefore write
$pH = - {\log _{10}}[{H^ + }]$ ……$\left( 1 \right)$
Here we are given hydrochloric acid. The molecular formula of hydrochloric acid is $HCl$ . The molar concentration of hydrochloric acid given is $0.05M$.
When $HCl$ is dissolved in water, it is given one ${H^ + }$ ion. So, $0.05M$ will give $1 \times 0.05M$ hydrogen ions which can be written as
$[{H^ + }] = 0.05M$
$[{H^ + }] = $ Concentration of hydrogen ions
Putting this value in equation $\left( 1 \right)$ , we get
$pH = - {\log _{10}}[{H^ + }]$
$ \Rightarrow pH = - \log [0.05]$…… $\left( 2 \right)$
$0.05$ can be written as $5 \times {10^{ - 2}}$. Substituting this value in $\left( 2 \right)$
$ \Rightarrow pH = - \log [5 \times {10^{ - 2}}]$
$ \Rightarrow pH = 1.3$

Thus, $pH$ is $1.3$.

Note: It is important to note $pH$ of a neutral is $7$. All the values of $pH$ which are less than $7$ are acidic in nature. Lesser is the value of $pH$, more acidic in nature. Values of $pH$ greater than $7$ are basic in nature. Also $pH + pOH = 14$