Calculate the pH of the buffer solution using the Ka for acetic acid. The buffer

Question

Calculate the pH of the buffer solution using the Ka for acetic acid.

The buffer is made of 20.00 mL of 0.100 M sodium hydroxide and 40.00 mL of 0.100 M acetic acid.

The ka of acetic acid is 1.75 x 10-5.

Please show work.

Buffers Hydrolysis and 102 Part 2- Buffer Solution: Calculated pH (from Measured pH below) Contents of Beaker Buffer Solution only Buffer Solution plus 1 M HCl 2.LIb 2) Water plus 1 M HCl 3) Buffer Solution plus 6 M HCI 4 Buffer Solution plus 11 51 1 M NaOH 5) Water plus 1 M 0.29 NaOH 6) Buffer Solution plus 6 M NaOH SHOW YOUR WORK FOR THE CALCULATIONS. 1) Calculate the pH of the buffer solution based on the known Ka value for acctic acid. pH known value of K, for acetic acid.

Explanation / Answer

Calculate moles of acetic acid

Mol = molarity x volume

0.040 L x 0.1 M = 0.004 mol CH3COOH

Calculate moles of NaOH

0.02 L x 0.1 M = 0.002 mol NaOH

Write reaction between CH3COOH and NaOH

CH3COOH + NaOH-- > CH3COONa + H2O

Mol ratio is 1:1

Using mol ratio calculate moles of acetic acid and NaOH at equilibrium

Mole of NaOH required to react with 0.004 mol CH3COOH

0.004 mol CH3COOH x 1 mol NaOH / 1 mol CH3COOH = 0.004 mol NaOH

But actually, there are only 0.002 mol NaOH, therefore NaOH is limiting reactant.

Calculate equilibrium moles

Moles of acetic acid = 0.004-0.002 mol = 0.002 mol acetic acid.

Moles of NaOH = 0.002 – 0.002 = 0

Moles of CH3COONa = 0.002 mol

Use Henderson Hasselbach equation.

pH = pka + log ([NaCH3COO]/[Ch3COOH])

since volume is same, we can take mol ratio of both and we will get

pH = -log ( ka) + log (0.002/0.002)

pH = - log ( 1.75 E-5) + log (1)

pH = 4.76

answer : 4.76

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