Can someone please help me answer these questions? Is additional information other than what is given needed to solve? Thanks in advance.
1) Calculate the PH of a buffer containing 0.100 M propanoic acid, HC3H5O2 and .100 M NaC3H502 after the following have been added. Ka for acetic acid is 1.3 x 10^-5.
a. 10.0 mL of 2.0 M HCl (assume no volume change occurs when acid is added)
b. 10.0 mL of 2.0 M NaOH (assume no volume change occurs when base is added)
2) A hydrofluoric acid buffer solution has the following concentrations: [HF] = .18M, [F-]= .51M. If 35mL of .15M NaOH is added to 354 mL of the buffer, what is the resultant pH?
#1 has no volume.
#2.
millimols HF = 354 mL x 0.18 = about 64
mmols F^- = 354 mL x 0.51 = about 180
added NaOH = 35 mL x 0.15 = about 5
.........HF + OH^- ==> F^- + H2O
I........64....0.......180
add............5..............
C.......-5....-5.........+5
E.......59.....0.......185
Substitute into HH equation and solve for pH. NOTE: My "abouts" are estimates. You need to redo each more accurately.
To solve these questions, you need to understand the concept of buffers and the Henderson-Hasselbalch equation.
1) Calculate the pH of a buffer containing 0.100 M propanoic acid, HC3H5O2, and 0.100 M NaC3H502 after the following have been added. Ka for acetic acid is 1.3 x 10^-5.
a. 10.0 mL of 2.0 M HCl
b. 10.0 mL of 2.0 M NaOH
To solve this question, you first need to recognize that propanoic acid (HC3H5O2) is a weak acid that can act as a buffer when combined with its conjugate base (C3H5O2-). The Henderson-Hasselbalch equation relates the pH of a buffer solution to the pKa (the negative logarithm of the acid dissociation constant) and the concentrations of the acid and its conjugate base.
Given:
- Concentration of propanoic acid (HC3H5O2) = 0.100 M
- Concentration of conjugate base (C3H5O2-) = 0.100 M
- Ka (acid dissociation constant) for acetic acid = 1.3 x 10^-5
a. For the addition of 10.0 mL of 2.0 M HCl:
- Since the volume change is assumed to be negligible, the final volume remains the same.
- You can calculate the number of moles of HCl added using the formula: moles = concentration × volume.
- Convert the moles of HCl to moles of propanoic acid by assuming they react in a 1:1 ratio. The moles of propanoic acid will decrease, and the moles of the conjugate base will increase.
- Use the Henderson-Hasselbalch equation: pH = pKa + log([C3H5O2-] / [HC3H5O2]).
- Substitute the concentrations of the conjugate base and propanoic acid, and solve for pH.
b. For the addition of 10.0 mL of 2.0 M NaOH:
- Again, assume negligible volume change, so the final volume remains the same.
- Calculate the moles of NaOH added using the formula: moles = concentration × volume.
- Convert the moles of NaOH to moles of the conjugate base (C3H5O2-) using the balanced chemical equation, assuming 1:1 reaction.
- Use the Henderson-Hasselbalch equation: pH = pKa + log([C3H5O2-] / [HC3H5O2]).
- Substitute the concentrations of the conjugate base and propanoic acid (after the addition of NaOH), and solve for pH.
2) A hydrofluoric acid buffer solution has the following concentrations: [HF] = 0.18 M, [F-] = 0.51 M. If 35 mL of 0.15 M NaOH is added to 354 mL of the buffer, what is the resultant pH?
To solve this question, you need to understand the concept of the common ion effect and the Henderson-Hasselbalch equation.
Given:
- Concentration of HF (hydrofluoric acid) = 0.18 M
- Concentration of F- (fluoride ion) = 0.51 M
- Volume of buffer = 354 mL
- Volume of NaOH added = 35 mL
- Concentration of NaOH = 0.15 M
- The hydrofluoric acid (HF) and fluoride ion (F-) act as a conjugate acid-base pair and form a buffer solution.
- The Henderson-Hasselbalch equation can be used to determine the pH of the buffer solution.
- The common ion effect needs to be considered when calculating the pH after addition of NaOH.
To solve:
1. Calculate the number of moles of HF and F- in the initial buffer solution.
- Moles = concentration × volume.
2. Calculate the number of moles of NaOH added to the buffer.
- Moles = concentration × volume.
3. Determine the new concentrations of HF and F- after the addition of NaOH.
- Subtract the moles of NaOH from the initial moles of HF and F-.
4. Use the Henderson-Hasselbalch equation: pH = pKa + log([F-] / [HF]), where pKa is the negative logarithm of the acid dissociation constant for HF.
5. Substitute the new concentrations of F- and HF into the equation and solve for pH.
Remember to consider the common ion effect, where the addition of NaOH will cause the concentration of F- to increase while the concentration of HF decreases, affecting the pH of the buffer solution.