A solution is prepared by dissolving of pure HC2H3O2 and of NaC2H3O2 in of solution (the final volume).
(a)
What is the pH of the solution?
(b)
What would the pH of the solution be if of 0.250 M NaOH were added?
(c)
What would the pH be if of 0.40 M HCl were added to the original of buffer solution?
I've answered this before. Use the Henderson-Hasselbalch equation. You don't get anywhere by just recopying the problem; however, if you show what you're tried and/or tell us what you don't understand about the solution we should be able to help you thorough it.
To determine the pH of the solution, as well as the effect of adding NaOH or HCl, we need to understand the concept of a buffer solution and how its pH is calculated. A buffer solution resists changes in pH when small amounts of acid or base are added to it.
(a) To find the pH of the original solution, we need to calculate the pH of a buffer solution consisting of a weak acid (HC2H3O2) and its conjugate base (C2H3O2-).
1. Calculate the initial concentration of both the weak acid and its conjugate base:
- Initial concentration of HC2H3O2 = 0.15 * (10/30) = 0.05 M
- Initial concentration of NaC2H3O2 = 0.25 * (20/30) = 0.167 M
2. Use the Henderson-Hasselbalch equation to calculate the pH:
pH = pKa + log([conjugate base] / [weak acid])
- The pKa of acetic acid (HC2H3O2) is 4.74.
- [conjugate base] = concentration of NaC2H3O2 = 0.167 M
- [weak acid] = concentration of HC2H3O2 = 0.05 M
pH = 4.74 + log(0.167/0.05)
Solve the equation to find the pH.
(b) To determine the pH after adding 20 mL of 0.250 M NaOH to the original solution, we need to calculate the new concentrations and the resulting pH.
1. Calculating the new concentration of the weak acid and conjugate base after the addition of NaOH:
- Moles of NaOH added = concentration * volume = 0.250 M * (20/1000) L
- Moles of NaOH = Moles of NaC2H3O2 (since NaOH reacts with NaC2H3O2 in a 1:1 ratio)
- Change in concentration of NaC2H3O2 = moles of NaOH added / final volume
- Change in concentration of HC2H3O2 = -moles of NaOH added / final volume (due to the 1:1 reaction ratio)
2. Calculate the new concentrations of the weak acid and its conjugate base:
- New concentration of HC2H3O2 = initial concentration of HC2H3O2 + change in concentration of HC2H3O2
- New concentration of NaC2H3O2 = initial concentration of NaC2H3O2 + change in concentration of NaC2H3O2
3. Use the Henderson-Hasselbalch equation to calculate the new pH as in part (a), but using the new concentrations.
(c) To determine the pH after adding 10 mL of 0.40 M HCl to the original buffer solution, we need to follow a similar process as in part (b):
1. Calculate the new concentrations of the weak acid and its conjugate base after the addition of HCl:
- Moles of HCl added = concentration * volume = 0.40 M * (10/1000) L
- Change in concentration of HC2H3O2 = -moles of HCl added / final volume
- Change in concentration of NaC2H3O2 = 0 (since HCl does not react with NaC2H3O2)
2. Calculate the new concentrations of the weak acid and its conjugate base:
- New concentration of HC2H3O2 = initial concentration of HC2H3O2 + change in concentration of HC2H3O2
- New concentration of NaC2H3O2 remains the same
3. Use the Henderson-Hasselbalch equation to calculate the new pH as in part (a), but using the new concentrations.
Remember to calculate the concentrations consistently in molarity (abbreviated M) and the final volume consistently in liters (L) for accurate results.