You will prepare two acidic buffer solutions (HC_2H_3O_2/NaC_2H_3O_2)of the same

Question

You will prepare two acidic buffer solutions (HC_2H_3O_2/NaC_2H_3O_2)of the same pH (pH-4), but different concentrations of the components. Use the Henderson-Hasselbalch equation to perform the following calculations that you will need for the experiment. The K_a of acetic acid is 1.8 times 10^-5. a) Buffer A: Calculate the mass of solid sodium acetate, NaC_2H_3O required to mix with 100.0 mL of 0.10 M acetic acid to prepare a pH 4 buffer. Record the mass in your data table. b) Buffer B: Calculate the mass of solid sodium acetate required to mix with 1000 mL of 1.0 M acetic acid to prepare a pH 4 buffer. Record the mass in your data table.

Explanation / Answer

Q5.

Buffer A:

mass of NaC require dfor

V = 100 mL of M = 0.1 M acetate

pH = pKa + log(A-/HA)

4 = 4.75 + log(NaAc / 0.1)

[NaAc] = 0.1 * 10^(4-4.75) = 0.017782 M

mol = MV = 0.017782*0.1 = 0.0017782 mol

MW of NAAC = 82 g/mol

mass = mol*MW = 0.017782*82 = 1.458124 g of sodium acetate

B)

Buffer B::

similar... now M = 1

pH = pKa + log(A-/HA)

4 = 4.75 + log(NaAc / 1)

[NaAc] = 0.1 * 10^(4-4.75) = 0.017782 M

mol = MV = 0.017782*1= 0.017782 mol

MW of NAAC = 82 g/mol

mass = mol*MW = 0.017782 *82 = 14.58124 g of sodium acetate

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