Question

The pH of a mixture of 100 ml of 0.5 $HCl$ and 100 ml of 0.6 N $NaOH$ solution is:
A. 10.5
B. 1.3
C. 12.7
D. 4.7

Answer 1

Hint pH generally denotes the potential of hydrogen or power of hydrogen. It is a scale which is used to tell the given aqueous solution is acidic or basic in nature. pH of aqueous solutions can be measured by pH meter or color changing indicator.

Complete Step by step solution:
pH scale is logarithm which inversely indicates the concentration of hydrogen ions present in the solution in this pH is the negative of the base 10 logarithmic of the activity of ${{H}^{+}}$ ion. The pH of hydroxide ion and hydrogen ion combine have value of 14 which can be represented as:
$pH+pOH=14$
In this case we consider the formula for hydroxide ion concentration which can be shown as:
${{[OH] }^{-}}=\dfrac{{{N}_{2}}{{V}_{2}}-{{N}_{1}}{{V}_{1}}}{{{V}_{1}}+{{V}_{2}}}$
Where ${{N}_{1}}$ = Normality of $HCl$ = 0.5 N, ${{N}_{2}}$ = Normality of $NaOH$ = 0.6 N, ${{V}_{I}}$ = Volume of HCl = 100 ml i.e. 0.1 L and ${{V}_{2}}$ = Volume of $NaOH$ = 100 ml i.e. 0.1 L
Now put all the values in the formula
${{[OH] }^{-}}=\dfrac{0.6\times 0.1-0.5\times 0.1}{0.1+0.1}=0.05M$
Now like pH, pOH is also negative of the base 10 logarithmic of the activity of $O{{H}^{-}}$ and this can be represented as:
$pOH=-\log [O{{H}^{-}}] =-\log 0.05=1.3$
And from this we can easily calculate the pH value as we know that $pH+pOH=14$
$\therefore pH=14-pOH=14-1.3=12.7$

Hence from the above calculations we can say that option C is the correct answer.

Note: The solutions which have pH value less than 7 are basic in nature, values greater than 7 are basic in nature while those solutions which value pH exactly 7 are neutral in nature generally distilled water is the only solution which is known to be neutral.