Question

If the pH of a solution is increased from 3 to 6, then ${{\text{H}}^ + }$ ion concentration of the solution will be:
A) Increased by 1000 times
B) Reduced to half
C) Reduced by 100 times
D) Reduced by 1000 times.

Answer 1

We know that pH measures the acidity of an acid or it measures how easily an acid gives away a proton. To solve this we must know the relation between pH and the hydrogen ion concentration. First calculate the hydrogen ion concentration at pH 3 and pH 6 and then find the change in the hydrogen ion concentration.

Formula Used:
${\text{pH}} = - \log [{{\text{H}}^ + }]$

Complete step by step answer: We know that pH is the negative logarithm of the hydrogen ion concentration. Thus,
${\text{pH}} = - \log [{{\text{H}}^ + }]$
Thus,
$[{{\text{H}}^ + }] = {10^{ - {\text{pH}}}}$
Using the above equation, calculate the concentration of hydrogen ion ${\text{(}}{{\text{H}}^ + })$ when the pH of the solution is 3. Thus,
$[{{\text{H}}^ + }] = {10^{ - 3}}$
Using the above equation, calculate the concentration of hydrogen ion ${\text{(}}{{\text{H}}^ + })$ when the pH of the solution is 6. Thus,
$[{{\text{H}}^ + }] = {10^{ - 6}}$
The ${{\text{H}}^ + }$ ion concentration of the solution when pH is 3 is ${10^{ - 3}}$ and the ${{\text{H}}^ + }$ ion concentration of the solution when pH is 6 is ${10^{ - 6}}$. Thus, the pH is reduced by 1000 times.
Thus, if the pH of a solution is increased from 3 to 6, then ${{\text{H}}^ + }$ ion concentration of the solution will be reduced by 1000 times.
Thus, the correct option is (C) reduced by 1000 times.

Note: The ${{\text{H}}^ + }$ ion concentration of the solution when pH is 3 is ${10^{ - 3}}$ and the ${{\text{H}}^ + }$ ion concentration of the solution when pH is 6 is ${10^{ - 6}}$. Thus, we can say that as the pH increases the hydrogen ion concentration decreases or vice versa. Thus, the hydrogen ion concentration is inversely proportional to the pH. Here, both solutions have pH 3 and 7 which are less than 7. Thus, both the given solutions are acidic.