Calculate the pH of a solution that is 0.185M in HC2H3O2 and 0.125M in KC2H3O2
To calculate the pH of a solution of a weak acid and its conjugate base, you can use the Henderson-Hasselbalch equation:
pH = pKa + log([A-]/[HA])
where:
- pH is the desired pH of the solution
- pKa is the dissociation constant of the weak acid
- [A-] is the concentration of the conjugate base
- [HA] is the concentration of the weak acid
In this case, HC2H3O2 (acetic acid) is a weak acid and KC2H3O2 (potassium acetate) is its conjugate base.
First, we need to find the pKa value for acetic acid. The pKa of acetic acid is 4.76.
Using the Henderson-Hasselbalch equation, we can plug in the given values:
pH = 4.76 + log([KC2H3O2]/[HC2H3O2])
Now, let's substitute the concentrations:
pH = 4.76 + log(0.125/0.185)
Next, perform the calculation:
pH = 4.76 + log(0.6757)
Using a calculator, find the logarithm of 0.6757:
pH ≈ 4.76 + (-0.17)
Finally, calculate the pH:
pH ≈ 4.59
Therefore, the pH of the solution is approximately 4.59.
To calculate the pH of a solution with HC2H3O2 and KC2H3O2, we need to use the concept of the acid dissociation constant (Ka) and the Henderson-Hasselbalch equation.
Step 1: Write the balanced chemical equation for the dissociation of HC2H3O2:
HC2H3O2(aq) ⇌ H+(aq) + C2H3O2-(aq)
Step 2: Find the equilibrium concentration of H+ ion. Since HC2H3O2 is a weak acid, we can assume that it does not completely dissociate. Therefore, the equilibrium concentration of H+ is the same as the initial concentration of HC2H3O2, which is 0.185M.
Step 3: Find the concentration of the conjugate base, C2H3O2-. Since KC2H3O2 is a salt of the conjugate base, it dissociates completely in water. Therefore, the concentration of C2H3O2- is the same as the initial concentration of KC2H3O2, which is 0.125M.
Step 4: Calculate the pH using the Henderson-Hasselbalch equation:
pH = pKa + log([conjugate base]/[acid])
To use the Henderson-Hasselbalch equation, we need to know the pKa value of HC2H3O2. The pKa value is a measure of the acidity or strength of an acid.
The pKa value of HC2H3O2 is approximately 4.76.
Now we can substitute the values into the Henderson-Hasselbalch equation:
pH = 4.76 + log(0.125/0.185)
Calculating the right side of the equation:
pH = 4.76 + log(0.6757)
Finally, calculate the logarithm using a calculator:
pH ≈ 4.76 + (-0.1704)
pH ≈ 4.59
Therefore, the pH of the solution is approximately 4.59.