Question

The pH of a solution is 2.57 at 25 degrees C. What is the molar concentration of hydronium ions? What is the molar concentration of hydroxide ions?

The pH of a solution is 2.57 at 25 degrees C.

What is the molar concentration of hydronium ions?
What is the molar concentration of hydroxide ions?

Answer 1

Given the definition of `pH`, I can write immediately that if `pH=2.57`, then `[H_3O^+]=10^(-2.57)` `mol*L^-1`

Explanation:

And also given the definitions, I know that `[H_3O^+][HO^-]=10^-14` under standard condtions; taking `log_10` of both sides, this gives our defining relationship:

`pH+pOH=14`

And thus `pOH` `=` `{14-2.57}`, and `HO^-` `=` `10^(-11.43)*mol*L^-1`.

Of course you will need a calculator to assess these values. I have never got one handy.

In a neutral solution at `298*K`, the equilibrium operates, `[H_3O^+][HO^-]=10^-14`, and `pH` `=` `pOH` `=` `7`. At temperatures higher than `298K`, how would you expect `pH` to evolve in a neutral solution. Would it increase, decrease, stay the same?