Question

pH of $10^{-1}$ M formic acid is:
A. 1
B. >1
C. <1
D. 13

Answer 1

Hint: The PH of solution is defined as a negative logarithm of its ${H^ + }$ ion or ${H_3}{O^ + }$ ion concentration. Hence, by using the below formula we can calculate the above numerical.

Formula used:
$PH = - \log [{H_3}{O^ + }]$
$PH = \log \dfrac{1}{{[{H_3}{O^ + }]}}$

Complete step by step answer: Since, we know the molecular formula for formic acid is $HCOOH$ and when formic acid get dissociate it gives ${H^ + }$ ion as shown in the below equation:
$HCOOH\xrightarrow{{}}HCO{O^ - } + {H^ + }$

Now, given the molar concentration of $HCOOH$ is ${10^{ - 1}}$ M. Since one formic acid on dissociation gives one ${H^ + }$ ion. Hence, we can say the molar concentration of ${H^ + }$ ion is also ${10^{ - 1}}$. So, by using the formula:
$PH = - \log [{H_3}{O^ + }] = - \log [{H^ + }]$
$ \Rightarrow PH = - \log {10^{ - 1}}$
$ \Rightarrow PH = - ( - 1)\log 10$
$ \Rightarrow PH = \log 10$
As we know the value of $\log 10$ is $1$

Then $PH = 1$

Hence, the correct answer is option (A).

Additional Information:
PH is also defined as the negative power to which 10 must be raised to equal the hydrogen ion concentration. It is used to know the nature of an aqueous solution. The acidic, basic and neutral nature of an aqueous solution depends upon the concentration of ${H^ + }$ ions or $O{H^ - }$ ions.

Note:
To measure the concentration of hydronium ion or hydrogen ion we use a scale which is known as the PH scale. The PH scale was devised by Sorenson in 1909. If the concentration of hydronium ion is greater than ${10^{ - 7}}$ then the solution is acidic and when the concentration of hydronium ion is less than ${10^{ - 7}}$ then the solution is basic and when the concentration is equal to ${10^{ - 7}}$ then the solution is neutral.