Buffers Prelaboratory Assignment Name and Drawer Number 1. A 10.00 mL portion of

Question

Buffers Prelaboratory Assignment Name and Drawer Number 1. A 10.00 mL portion of acetic acid was added to an Erlenmeyer flask with a pipette and titrated to the end point with 16.30 mL of 0.1087 M NaOH(aq) a. Write the balanced chemical equation for the titration reaction. b. Use the balanced chemical equation, the volume of acetic acid, and the volume and concentration of sodium hydroxide to calculate the concentration of the acetic acid solution. 2. Calculate (H'] for a pH 4.80 solution by using the mathematical definition of pH [Equation (21-1) 3. A pH 4.80 buffer solution is prepared by adding solid sodium acetate trihydrate NaC2H:02 3H20 to 50.0 mL of the acetic acid solution that was standardized in problem 1. Use Equation (22-3) with the acetic acid concentration calculated in problem 1, the K, for acetic acid (K.-1.8 x 10-) and the concentration of H' calculated in problem 2 to calculate (a) the concentration of acetate in the buffer solution and (b) the mass of sodium acetate trihydrate required to prepare the solution with that concentration. Assume the addition of the solid does not change the solution volume. Remember that the water in the formula of a hydrate must be included in calculating molar mass of a hydrate. -150-

Explanation / Answer

Q1)a)

The balanced equation for the titration is

CH3COOH (aq) + NaOH (aq) -----------------> CH3COONa (aq) + H2O(l)

b) From the balanced equation

mmoles of acid = mmoles of base at equivalence

10mL x Molarity = 16.3mL x 0.1087

thus molarity of acid = 0.1771 M

Q2)

The pH of solution = 4.8

By definition the pH of a solution is negative logarithm of H+ ion concnetration

Thus pH = -log [H+]

4.8 = - log [H+]

and [H+] = Antilog (-4.8)

= antilog (bar5.2)

= 1.585x10-5 M

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