Answer:
This question is incomplete, here's the complete question:
1. Calculate the concentration of hydronium ion of both buffer solutions at their starting pHs. Calculate the moles of hydronium ion present in 20.0 mL of each buffer.
Buffer A
Mass of sodium acetate used: 0.3730 g
Actual ph of the buffer 5.27
volume of the buffer used in buffer capacity titration 20.0 mL
Concentration of standardized NaOH 0.100M
moles of Naoh needed to change the ph by 1 unit for the buffer 0.00095mol
the buffer capacity 0.0475 M
Buffer B
Mass of sodium acetate used 1.12 g
Actual pH of the buffer 5.34
Volume of the buffer used in buffer capacity titration 20.0 mL
Concentration if standardized NaOH 0.100 M
moles of Naoh needed to change the ph by 1 unit 0.0019 mol
the buffer capacity 0.095 M
2.) A change of pH by 1 unit means a change in hydronium ion concentration by a factor of 10. Calculate the number of moles of NaOH that would theoretically be needed to decrease the moles of hydronium you calculated in #1 by a factor of 10 for each buffer. Are there any differences between your experimental results and the theoretical calculation?
3.) which buffer had a higher buffer capacity? Why?
Explanation:
Formula,
moles = grams/molar mass
molarity = moles/L of solution
1. Buffer A
molarity of NaC2H3O2 = 0.3731 g/82.03 g/mol x 0.02 L = 0.23 M
molarity of HC2H3O2 = 0. 1 M
Initial pH
pH = pKa + log(base/acid)
= 4.74 + log(0.23/0.1)
= 5.10
pH = -log[H3O+]
[H3O+] = 7.91 x 10^-6 M
In 20 ml buffer,
moles of H3O+ = 7.91 x 10^-6 M x 0.02 L
= 1.58 x 10^-7 mol
Buffer B
molarity of NaC2H3O2 = 1.12 g/82.03 g/mol x 0.02 L = 0.68 M
molarity of HC2H3O2 = 0.3 M
Initial pH
pH = pKa + log(base/acid)
= 4.74 + log(0.68/0.3)
= 5.10
pH = -log[H3O+]
[H3O+] = 7.91 x 10^-6 M
In 20 ml buffer,
moles of H3O+ = 7.91 x 10^-6 M x 0.02 L
= 1.58 x 10^-7 mol
2. let x moles of NaOH is added,
Buffer A,
pH = 5.10
[H3O+] = 7.91 x 10^-6 M
new pH = 4.10
new [H3O+] = 7.91 x 10^-5 M
moles of NaOH to be added = (7.91 x 10^-5 - 7.91 x 10^-6) x 0.02 L
= 1.42 x 10^-6 mol
3. Buffer B with greater concentration of NaC2H3O2 and HC2H3O2 has higher buffer capacity as it resists pH change to a wider range due to addition of acid or base to the system as compared to low concentration of Buffer A
