You are instructed to create 190. mL of a 0.13 M Acetate buffer with a pH of 4.1

Question

You are instructed to create 190. mL of a 0.13 M Acetate buffer with a pH of 4.1. You have Acetic acid and the sodium salt NaC2H3O2, available. (Enter all numerical answers to three significant figures.)

What is the molarity needed for the acid component of the buffer?

What is the molarity needed for the base component of the buffer?

How many moles of acid are needed for the buffer?

How many moles of base are needed for the buffer?

How many grams of acid are needed for the buffer?

How many grams of base are needed for the buffer?

Explanation / Answer

total moles of acetate buffer = 190 x 0.13 / 1000 = 0.0247

pH = 4.1

Ka = 1.7 x 10^-5

pKa = 4.77

pH = pKa + log [salt / acid]

4.1 = 4.77 + log [NaC2H3O2 / HC2H3O2]

[NaC2H3O2 / HC2H3O2] = 0.214

[NaC2H3O2 + HC2H3O2] = 0.0247

0.214 HC2H3O2 + HC2H3O2 = 0.0247

HC2H3O2 = 0.02035

moles of acid needed = 0.0204

moles of base needed = 0.00435

Molarity of acid component = 0.107 M

Molarity of base = 0.0229 M

mass of acid needed = 1.22 g

mass of base needed = 0.357 g

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