You are instructed to create 180. mL of a 0.12 M Acetate buffer with a pH of 4.3

Question

You are instructed to create 180. mL of a 0.12 M Acetate buffer with a pH of 4.3. You have Acetic acid and the sodium salt NaC2H3O2, available. (Enter all numerical answers to three significant figures.)

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

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

3. How many moles of acid are needed for the buffer?

4. How many moles of base are needed for the buffer?

5. How many grams of acid are needed for the buffer?

6 . How many grams of base are needed for the buffer?

Explanation / Answer

pH = 4.3

Ka = 1.7 x 10^-5

pKa = 4.77

total moles of acetate buffer = 180 x 0.12 / 1000 = 0.0216

pH = pKa + log [salt / acid]

4.3 = 4.77 + log [NaC2H3O2 / HC2H3O2]

[NaC2H3O2 / HC2H3O2] = 0.3388

[NaC2H3O2 + HC2H3O2] = 0.0216

0.3388 HC2H3O2 + HC2H3O2 = 0.0216

HC2H3O2 = 0.0161

moles of acid needed = 0.0161

moles of base needed = 0.0055

Molarity of acid = 0.089 M

Molarity of base = 0.0304 M

mass of acid = 0.966 g

mass of base = 0.451 g

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