Question

Experiment 2: Using the Secondary Standard to Determine the Concentration of an Acid

1. In an Erlenmeyer flask, add 25 mL of Unknown #1 concentration of acetic acid (CH₃COOH) and 2 drops of phenolphthalein indicator.

2. Coarse Titration:

(a) Take a burette from the Containers shelf and place it on the workbench. Fill the burette with 50 mL of the standardized sodium hydroxide solution. Record the initial burette reading. Place the Erlenmeyer flaskon the lower half of the burette.

(b) Perform a coarse titration, adding large increments of the sodium hydroxide solution from the buretteby pressing and holding the black knob at the bottom of the burette. Each time you add the sodium hydroxide solution, check the volume remaining in the burette. As the sodium hydroxide is added to the acetic acid solution the pH increases. Watch for a change of the phenolphthalein color in the Erlenmeyer flask. The pink color will appear in Erlenmeyer flask when the endpoint is either reached or crossed. Record the burette volume at which this occurs.

(c) Place the Erlenmeyer flask and the burette in the recycling bin.

3. Fine Titration:

(a) Set up the tiration as before: (i) An Erlenmeyer flask filled with 25 mL of unknown #1 concentration of acetic acid and 2 drops of phenolphthalein indicator. (ii) A burette filled with 50 mL of the standardizedsodium hydroxide solution. Record the initial burette reading. (iii) Place the Erlenmeyer flask on the lower half of the burette.

(b) Click and hold the black knob of the burette to quickly add enough standard sodium hydroxide solution to just get into the range of the coarse titration: 1 mL BEFORE the pink endpoint. This is near, but not yet at, the titration's endpoint.

(c) Add sodium hydroxide solution in small increments, down to one drop at a time, record the volume of the pink endpoint.

(d) Place the Erlenmeyer flask and the burette in the recycling bin.

4. Repeat the titration two more times for a total of three trials. Use 30mL of acetic acid for trial 2 and 35mL for trial 3. Calculate the acid concentration of each trial.
[If you run out of NaOH, simply prepare a second solution as described in step 2 of Exp. 1. You don’t need to standardize it a second time. Assume the standardized concentration is the same as before.]

In the space below, show your calculation(s) for approximating the molarity of a 200.0 mL solution containing 0.8 g NaOH so molarity of NaOH is 0.10mol/L?

Need help with the B, C, D, E, F, G and the calculation part

Trial 1              Trial 2              Trial 3

a) Volume of acid (mL)                                     25.1mL             30.1mL            35.1mL

b) Volume of NaOH titrated (mL)                     _____              _____              _____

c) Moles of NaOH titrated                                 _____              _____              _____

d) Moles of acid                                               _____              _____              _____

e) Concentration of acid (M)                             _____              _____              _____

f) Average acid concentration (M)                                             _____

Using your Trial 1 data, show you work for calculating each of the following:

Moles of NaOH titrated

Moles of acid

Concentration of acid

Answer 1

Problem 4.

b) The volume of NaOH titrated

Trial 1 = 200 - 25.1 = 174.9 mL

Trial 2 = 200 - 30.1 = 169.9 mL

Trial 3 = 200 - 35.1 = 164.9 mL

c) Moles of NaOH titrated

Trial 1 = 0.1 mol/L * (25.1/1000) L = 0.00251 mol

Trial 2 = 0.1 mol/L * (30.1/1000) L = 0.00301 mol

Trial 3 = 0.1 mol/L * (35.1/1000) L = 0.00351 mol

d) The moles of acid

Trial 1 = 0.00251 mol

Trial 2 = 0.00301 mol

Trial 3 = 0.00351 mol

e) Concentration of acid

Trial 1 = 0.00251 mol/0.2 L = 0.01255 M

Trial 2 = 0.00301 mol/0.2 L = 0.01505 M

Trial 3 = 0.00351 mol/0.2 L = 0.01755 M

f) The average acid concentraiton = (0.01255 + 0.01505 + 0.01755)/3 = 0.01505 M