# Calculate the pH of 100mL HOAc + 100mL Ba(OH)2

• Joules23
In summary, the pH of a solution containing 100mL of 0.20M HOAc and 100mL of 0.10M Ba(OH)2 is 12.7. However, using equivalents instead of moles, the situation becomes neutralized and the pH should be calculated using the Kb equation to find the [OH-] and further calculations to determine the pH.
Joules23

## Homework Statement

find the pH of:
100mL x .20M HOAc + 100mL x.10M Ba(OH)2

## The Attempt at a Solution

100x.2 = 20mmol HOAc
100x.1 = 10mmol Ba(OH)2
20-10=10
10/200=.05M
pOH = -log(.05) = 1.3
pH=14-1.3=12.7

Is this correct?

No. Ba(OH)2 is 'diprotic'.

Ba(OH)2 is not diprotic. Dibasic.

Think in terms of equivalents instead of moles (or mmol) with the barium hydroxide...

BTW, the way you did the work, it wasn't clear (to you) whether the "10" left over in the reaction was barium or acetic acid. Using the logic you provided, the acetic acid was actually present in excess and the pH should have been less than 7.

Using equivalents in place of moles should "completely neutralize" any misunderstanding you may have.

Joules23 said:

## Homework Statement

find the pH of:
100mL x .20M HOAc + 100mL x.10M Ba(OH)2

## The Attempt at a Solution

100x.2 = 20mmol HOAc
100x.1 = 10mmol Ba(OH)2
20-10=10
10/200=.05M
pOH = -log(.05) = 1.3
pH=14-1.3=12.7

Is this correct?

hint, hint, the situation is going to be "neutralized" as chemisttree has said

However, the conjugate of the acetic acid is a base with a significant Kb, you're going to need to use the Kb equation to find the [OH-], then the pH through further calculations.

chemisttree said:
Ba(OH)2 is not diprotic. Dibasic.

That's what happens when English is not your first language...

## 1. How do I calculate the pH of a solution containing both HOAc and Ba(OH)2?

To calculate the pH of a solution containing both HOAc and Ba(OH)2, you will need to use the Henderson-Hasselbalch equation. This equation is pH = pKa + log([A-]/[HA]), where pKa is the acid dissociation constant of HOAc, [A-] is the concentration of the conjugate base, and [HA] is the concentration of the acid. You will also need to consider the hydroxide ion concentration from Ba(OH)2 in your calculations.

## 2. What is the pKa value for HOAc?

The pKa value for HOAc, or acetic acid, is 4.76. This value is readily available in chemical reference books or online databases.

## 3. How do I determine the concentrations of HOAc and Ba(OH)2 in the solution?

You can determine the concentrations of HOAc and Ba(OH)2 by using the molarity (M) formula, which is M = moles of solute/volume of solution in liters. You will need to know the number of moles of each substance present in 100mL of solution in order to calculate their concentrations.

## 4. Can I use any other equation to calculate the pH of this solution?

Yes, you can also use the Kw (ionization constant for water) to calculate the pH. The equation is pH = 14 - pOH = 14 - log([OH-]), where [OH-] is the hydroxide ion concentration from Ba(OH)2. However, this method is only accurate if the concentration of HOAc is significantly greater than Ba(OH)2.

## 5. How does the addition of Ba(OH)2 affect the pH of the HOAc solution?

The addition of Ba(OH)2, a strong base, will increase the pH of the HOAc solution. This is because the hydroxide ions from Ba(OH)2 will react with the weak acid, HOAc, to form water and the conjugate base, A-. This decreases the concentration of HOAc and increases the concentration of the conjugate base, shifting the equilibrium towards the basic side of the pH scale.

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