Question

If pH of $0.1M$ solution of ${{\left( N{{H}_{4}} \right)}_{2}}C{{O}_{3}}\left( aq \right)$ is $x$ than pH of $0.01M$ solution of ${{\left( N{{H}_{4}} \right)}_{2}}C{{O}_{3}}\left( aq \right)$ would be?
A.More than $x$
B.Less than $x$
C.Equal to $x$
D.Unpredictable

Answer 1

In case of basic solutions, the value of pH is directly proportional to the concentration of the solution.
-This is because, when the concentration of hydroxide ion increases in a solution, the pH value also increases. Moreover, concentration of a solution can be expressed in terms of molarity.
Complete answer:
-We know that the pH of a solution is the measure of the acidic or basic nature of the solution. So, the concentration of ${{H}^{+}}$ and $O{{H}^{-}}$ ion generally determines the strength of acidic or basic nature of a solution. Which means, if the concentration of ${{H}^{+}}$ ions is more in a solution, it will have lower value of pH, and if the concentration of $O{{H}^{-}}$ ions is more in a solution then it will have higher value of pH. However in case of solutions, without the presence of hydroxide ion or proton, it can still have an acidic or basic nature, on the basis of their tendency to donate or accept electrons. As we know this is the Lewis theory of acid and bases, and the solvents which donates its lone pair of electrons are basic in nature and those which have an ability to accept lone pairs of electrons, are acidic in nature.
-Now we know that molarity of a solution is the concentration, in other words, it is the number of moles present per litre volume of the solution. And as the concentration of hydroxide increases in a solution, the pH increases and so does the basicity. So, with increase in molarity in a basic solution, the pH will also increase. And we know that the ${{\left( N{{H}_{4}} \right)}_{2}}C{{O}_{3}}\left( aq \right)$ is basic in nature. So, if at $0.1M$ concentration, it has pH value $x$ , when we decrease the concentration of this solution, the pH value should also decrease.
Hence the correct option would be B, as it has pH value less that $x$.

Note:
-The direct relationship between pH $x$ of the solution of ${{\left( N{{H}_{4}} \right)}_{2}}C{{O}_{3}}\left( aq \right)$ and the concentration of the same, is, directly proportional.
-In other words, with decrease in concentration of the solution, which was expressed in terms of molarity in this question, the pH value will also decrease.