Question

100ml of $0.1M$ $HCl$ is mixed with $100ml$ of 0.01M$$$$HCl .The $pH$ of the resulting solution is:
A. $2.0$
B. $1.0$
C. $1.26$
D. None of these

Answer 1

The term “$pH$” is an abbreviation for the “potential of hydrogen.” $pH$ is a unit of measurement which represents the concentration of hydrogen ions in a solution.

Complete step by step answer:
To calculate the $pH$ of an aqueous solution you need to know the concentration of the hydronium ion in moles per liter (molarity). The $pH$ is then calculated using the expression:
$pH = - \log {[{H_3}O]^ + }$
Calculating the Hydronium Ion Concentration from $pH$
The hydronium ion concentration can be found from the pH by the reverse of the mathematical operation employed to find the $pH$ .
${[{H_3}O]^ + } = {10^{ - pH}}$
Or
${[{H_3}O]^ + } = anti{\log ^{( - pH)}}$
Calculating $pOH$
To calculate the $pOH$ of a solution you need to know the concentration of the hydroxide ion in moles per liter (molarity). The $pOH$ is then calculated using the expression:
$pOH = - \log {[OH]^ - }$
Calculating the Hydroxide Ion Concentration from $pOH$
The hydroxide ion concentration can be found from the $pOH$ by the reverse mathematical operation employed to find the $pOH$ .
${[OH]^ - } = {10^{ - pOH}}$
Or
${[OH]^ - } = anti\log ( - pOH)$
Relationship Between and $pOH$ .
The $pH$ and $pOH$ of a water solution at 25$^\circ$C are related by the following equation.
$pH + pOH = 14$
Step by step solution: When you add two different concentrations of the same strong acid, the pH contribution will be from both concentrations.
$M_1 = 0.1M \\\ V_1 = 100ml \\\ M_2 = 0.01M \\\ V_2 = 100ml$
Final volume of solution is $100 + 100 = 200ml$
The final concentration of mixture will be calculated as
$MV = M_1V_1 + M_2V_2$
= $M(100 + 100) = 0.1 \times 100 + 0.01 \times 100M$
$M = 200(10 + 1) = 0.055M$
$pH = - \log [{H^ + }]$
=$- \log (0.055)$
=$1.259 \sim 1.26$

So, the correct answer is Option C.

Note: The $pH$ scale describes the acidity of the solution: acidic, neutral, or basic A solution with a $pH$ less than 7 is an acid, exactly 7 is a neutral solution, and above 7 is a base. Bases have less hydrogen ions but more hydroxide ions, represented by the $pOH$ or “potential of hydroxide ions.”

Acidic	Neutral	Basic
Less than 7	7	Greater than 7