JEE Chemistry 2023 Question with Solution

Given: The hydrogen ion concentration $[H^+]$ changes by a factor of $1000$.

Find: The change in pH of the solution.

Using the relation shown in the solution:

$$\Delta pH = -\log(\Delta[H^+])$$

Since

$$\Delta[H^+] = 1000 = 10^3$$

therefore,

$$\Delta pH = -\log(10^3) = -3$$

So, the pH decreases by $3$ units.

Discrepancy noted: The extracted solution text states "The Correct Option is A", but it also explicitly concludes "decreases by 3 units," which matches option B in the provided options. Therefore, the defensible correct option from the working is B.

Given: $\text{pH} = -\log[H^+]$ and $[H^+]$ changes by a factor of $1000$.

Find: How the pH changes.

If $[H^+]$ increases by a factor of $1000 = 10^3$, then from the logarithmic definition, pH changes by the negative logarithm of that factor:

$$\Delta \text{pH} = -\log(10^3)$$ $$\Delta \text{pH} = -3$$

A negative change means the pH decreases by $3$ units.

Therefore, the correct statement is decreases by $3$ units, which corresponds to option B among the listed options.