[Hotoke-sama]

Hi, im struggling with an Acid Concentration problem.
Part 1. If a solution is measured to have a pH=2.33, what is the concentration of H+ ions?
figured that out, its 4.68x10^-3 M using forumal pH=-log[H+]

second part.
suppose u titrate 10.0ml of the same solution( its a mixute of HNO2 and HNO3) and that you use 10.3mL of a .030-M Sodium Hydroxide solution to reach the end point.   Use these results to find the total acid concentration [HNO2]+[HNO3]

I figured out the first part but the second part is confusing me and I cant find any examples of problems similar to this. Some help would be really appreciated.

[Donaldson Tan]

Hi, im struggling with an Acid Concentration problem.
Part 1. If a solution is measured to have a pH=2.33, what is the concentration of H+ ions?
figured that out, its 4.68x10^-3 M using forumal pH=-log[H+]

you are on the right track.

second part.
suppose u titrate 10.0ml of the same solution( its a mixute of HNO2 and HNO3) and that you use 10.3mL of a .030-M Sodium Hydroxide solution to reach the end point.   Use these results to find the total acid concentration [HNO2]+[HNO3]

since each acid molecule (HNO2 and HNO3) contributes a H+ to the solution, hence the total acid concentration will be the [H+] of the solution.

[Borek]

since each acid molecule (HNO2 and HNO3) contributes a H+ to the solution, hence the total acid concentration will be the [H+] of the solution.

geodome: while in general you are right, what you have wrote can be misleading. [H+] observed in the solution - the one that can be measured with pH checking - is something different from the amount of H+ ions tritrable. Nitrous acid acid is a weak one with pKa = 3.37.

Hotoke-sama: geodome is right, but your calculations for the amount of H+ ions tittrated with NaOH will be different from the one obtained from pH. That's proper result! In the solution with pH = 2.33 not all HNO2 is dissociated and it will dissociate during titration, so there will be more H+ ions to neutralize than 4.68x10^-3 * 0.01.

[AWK]

since each acid molecule (HNO2 and HNO3) contributes a H+ to the solution, hence the total acid concentration will be the [H+] of the solution.

It is not true. HNO2 is a weak acid and H+ concentration comes from HNO3 only. But during titration both HNO2 and HNO3 are titrated. Hence total concentration of acids can be calculated directly from result of titration
10.0 x c_acids = 10.3 x 0.030