Question

Five solutions A, B, C, D, and E, when tested with a universal indicator, showed pH as $4,1,11,7,$ and $9$, respectively.

Which solution is -

(a) Neutral

(b) Strongly alkaline

(c) Strongly acidic

(d) Weakly acidic

Answer 1

$\mathrm{pH}$ (potential of Hydrogen):-

1. $\mathrm{pH}$ is defined as the negative logarithm to the base$10$, of the concentration of an ${\mathrm{H}}^{+}$ion in solution.
2. It is the indicator of the acidity or basicity of the solution.
3. It is given by $\mathrm{pH}=-\log \left[{\mathrm{H}}^{+}\right]$. The standard temperature for calculating $\mathrm{pH}$ is taken as $25°\mathrm{C}$.
4. $\mathrm{pH}$ scale ranges from $1$ to$14$.
5. The compound that has a value of $\mathrm{pH}$ in between$1-7$is acidic.
6. The compound having a value of $\mathrm{pH}$ in-between $7-14$ is basic.
7. The compound of $\mathrm{pH}$$7$is neutral.

Considering the given five solutions A, B, C, D, and E

(A) The neutral solution is D as its $\mathrm{pH}$ value is$7$ which is an ideal condition for a neutral solution, as per $\mathrm{pH}$ scale.

(B) Strongly alkaline solution is C as it has $\mathrm{pH}$ value $11,$ and as per $\mathrm{pH}$ scale, the solution which lies in the range of $7-14$is alkaline. But $11,$ is very close to$14$, which is the strongest alkaline $\mathrm{pH}$ value, therefore C is a strongly alkaline solution.

(C) Strongly acidic solution is B as it has $\mathrm{pH}$ value $1$ and as per $\mathrm{pH}$ scale, the solution which lies in the range of $1-7$is acidic. and $1$ is considered as the strongest acidic $\mathrm{pH}$ value, therefore B is a strongly acidic solution.

(D) A is a Weakly acidic solution is A as it has $\mathrm{pH}$ value $4$ and as per $\mathrm{pH}$ scale, the solution which lies in the range of $1-7$is acidic. But $4$ is in between $1-7$ which is not the strongest acidic $\mathrm{pH}$ value and not the weakest acidic $\mathrm{pH}$ value, therefore A is considered a weakly acidic solution.