You are instructed to create 50.0 mL of a 0.44 M Acetate buffer with a pH of 5.5

Question

You are instructed to create 50.0 mL of a 0.44 M Acetate buffer with a pH of 5.5. You have Acetic acid and the sodium salt NaC2H302, available. (Enter all numerical answers to three significant figures.) Write the results of your calculations in your lab notebook for use during lab. HC_2H_3O_2(s) + H_2O(I) H_3O^+(aq) + C_2H_3O_2^-(aq) K_a1 = 1.7 times 10^-5 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

Writing the equilibrium expression for this buffer:

HAc + H2O ---> Ac-(aq) + H3O+(aq)

0.44 - x M -------> x M + x M

Ka = 1.7 x 10^5 = x^2/(0.44 - x)

From here we calculate the amount of acid/base in the equilibrium:

x^2 + 1.7 x 10^-5 - 7.48 x 10^-6 = 0

x = 0.00273 M -> this is the molarity needed for both the acid and base components.

Molarity = moles/L of solution ---> moles = Molarity * L of solution

For both acid and base components:

moles = 0.00273 M * 0,05 L = 1,37 x 10^-4 moles

Acetic acid required for the buffer: 1,37 x 10^-4 mol x 60 g/mol = 0.00822 g

Sodium acetate required for the buffer: 1,37 x 10^-4 mol x 82 g/mol = 0,0112 g

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