Your assigned pH is: 5.0. You are to assume that the buffer is made up by mixing

ID: 1057745 • Letter: Y

Question

Your assigned pH is: 5.0. You are to assume that the buffer is made up by mixing volumes of 0.100 M acetic acid and 0.100 M sodium acetate solutions.

Calculate the volume of 0.100 M acetic acid required to prepare 60.0 mL of a buffer of pH 5.0.

Calculate the volume of 0.100 M sodium acetate required to prepare 60.0 mL of a buffer of pH 5.0.

Calculate the concentration [HA] in this buffer.

Calculate the concentration [A-] in this buffer.

Calculate the volume of 0.1000 M NaOH which would be required to titrate 20.0 mL of the buffer solution to the Basic equivalence point.

Calculate the pH at the Basic equivalence point.

Calculate the volume of 0.1000 M HCl which would be required to titrate 20.0 mL of the buffer solution to the Acidic equivalence point.

Calculate the pH at the Acidic equivalence point.

As per the Henderson-Hasselbalch equation, such that

pH = pKa + log[base]/[acid]

[base] is the final concentration of sodium acetate

[acid] is the final concentration of acetic acid

pH = pKa + log[A-]/[HA]

The pKa of acetic acid is 4.74 (pKa = -log Ka = -log 1.8x10-5)

5.0 = 4.74 + log[A-]/[HA]

0.26 = log[A-]/[HA]

1.8197 = [A-]/[HA]

[HA]1.8197 = [A-]

A- - 1.8197 HA = 0
A- + HA = 60.0 mL

2.8197HA=60 ml

HA = 21.27 ml

A-=38.72 ml

Moles NaOH = moles HA = (0.0500 moles/L)*(0.020 L) = 0.00100 moles
Volume NaOH = 0.00100 moles/(0.100 moles/L) = 0.0100 L = 10.0 mL

Moles HCl = moles A- = (0.0500 moles/L)*(0.020 L) = 0.00100 moles
Volume HCl = 0.00100 moles/(0.100 moles/L) = 0.0100 L = 10.0 mL

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