# Calculating the molar concentration of H3O+ and pH of solutions

• NYK
In summary, the molar concentration of H3O+ ions and the pH of the given solutions were calculated using the Henderson - Hasselbach equation. In the first case, 25.0 cm3 of 0.144 M HCl(aq) was added to 25.0 cm3 of 0.125 M NaOH(aq), resulting in a pH of 2.0. In the second case, 25.0 cm3 of 0.15 M HCl(aq) was added to 35.0 cm3 of 0.15 M KOH(aq), with the acid being the limiting reagent and resulting in a pH of 12.3. However, the calculated m
NYK

## Homework Statement

Calculate the the molar concentration of H3O+ ions and the pH of the following solutions:
a) 25.0 cm3 of 0.144 M HCl(aq) was added to 25.0 cm3 of 0.125 M NaOH(aq)
b) 25.0 cm3 of 0.15 M HCl(aq) was added to 35.0 cm3 of 0.15 M KOH(aq)
c) 21.2 cm3 of 0.22 M HNO3(aq) was added to 10.0 cm3 of 0.30 M NaOH(aq)

## Homework Equations

pH = -log[H3O+] Handerson - Hasselbach eqn.

## The Attempt at a Solution

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I have only been able to solve part a)

I did that by multiplying the molairty of the strong acid/base by the total volume

then: [H3O+] = [HCl] - [NaOH] = 9.5 x 10-3mol

then took the negative log of that number to find the pH = 2.0

which are the correct answers, but when I do that process for part b) and c) which are also strong acid/base combos, the answers are no where near correct.

Any help will be appreciated.

In the second case - what is the limiting reagent? What is left in the solution after the neutralization reaction took place?

Borek said:
In the second case - what is the limiting reagent? What is left in the solution after the neutralization reaction took place?

In the second case the LR is the acid. When i do that calculation I find that the [H3O+] = .04875 mol/L

the answer is 21 mmol/L and a pH = 12.3

NYK said:
In the second case the LR is the acid.

Good.

When i do that calculation I find that the [H3O+] = .04875 mol/L

the answer is 21 mmol/L and a pH = 12.3

I am afraid neither of these numbers is correct.

First of all - you said acid was the limiting reagent. If so, how come there is mo much H3O+ left?

21 mmol/L of what?

pH of 12.3 is quite close - but it is possible to easily give a better answer.

Strong acids and bases, so Henderson - Hasselbach eqn. never came into it.

## 1. How do you calculate the molar concentration of H3O+ in a solution?

The molar concentration of H3O+ (also known as the hydronium ion) can be calculated by dividing the number of moles of H3O+ by the volume of the solution in liters. This can be represented by the formula: Molarity (M) = moles of H3O+ / volume of solution (L).

## 2. What is the relationship between molar concentration of H3O+ and pH?

The molar concentration of H3O+ is directly related to the pH of a solution. As the molar concentration of H3O+ increases, the pH decreases, and vice versa. This can be represented by the equation: pH = -log[H3O+], where [H3O+] is the molar concentration of H3O+ in moles per liter.

## 3. How do you convert between molar concentration of H3O+ and pH?

To convert between molar concentration of H3O+ and pH, you can use the following equations: [H3O+] = 10-pH and pH = -log[H3O+]. Simply plug in the known value for one variable and solve for the other.

## 4. Can the molar concentration of H3O+ and pH be measured experimentally?

Yes, both the molar concentration of H3O+ and pH can be measured experimentally. The molar concentration can be determined by titration or by using a pH meter. The pH can be measured using a pH meter or by using acid-base indicators.

## 5. How does temperature affect the molar concentration of H3O+ and pH?

Temperature can affect the molar concentration of H3O+ and pH in a solution. As temperature increases, the molar concentration of H3O+ decreases, leading to an increase in pH. This is due to the fact that as temperature increases, water molecules become more mobile and can dissociate into H3O+ and OH- ions. Therefore, it is important to take temperature into account when calculating the molar concentration of H3O+ and pH of a solution.

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