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September 1, 2014

Homework Help: chemistry

Posted by Nick on Tuesday, April 8, 2008 at 11:39pm.

Lab: Determining Ka of Acetic Acid

Purpose: The purpose of this experiment is to determine the molar concentration of a sample of acetic acid and to calculate its Ka.

Materials:
phenolphthalein
125 mL Erlenmeyer flask
25 mL pipet and bulb
pH metre
acetic acid solution
burette
sodium hydroxide solution
2x150 mL beaker

Procedure
1. Recorde the molar concentraiton of the NaOH solution
2.Produce a table to record your data. It should have one column for volume of NaOH added and one column for pH
3. Obtain 50 mL of acetic acid and place it into a beaker
4.Place 50.0 mL of NaOH into the burette.
5. Pipet 25.0 mL of acetic acid into the Erlenmeyer flask. Add 2 drops of phenolphthalien to the acid.
6. Record the initial pH of the solution
7. Add 1.00 mL of NaOH from the burette to the Erlynmeyer until the pH reaches 5.00. Record the volume of two decimal places. Measure the pH of the solution each time you add NaOH.
8. Above pH = 5.00, add NaOH in 0.10 or 0.20 mL portions. Record the volume at which the phenophthalein turns pink.
9. Continue to add NaOH until the pH reaches 11.00. Above pH = 11.00, add 0.10 mL portions until the pH reaches 12.00.

Here are my results:
NaOH (ml) pH
0.00 2.58
1.00 3.57
2.00 3.89
3.00 4.12
4.00 4.29
5.00 4.44
6.00 4.58
7.00 4.73
8.00 4.88
9.00 5.04
9.20 5.09
9.40 5.12
9.60 5.17
9.80 5.21
10.00 5.26
10.20 5.32
10.40 5.39
10.60 5.42
10.80 5.52
11.00 5.61
11.20 5.74
11.40 6.11
11.60 6.26
11.80 6.50
12.00 10.66
12.20 11.19
12.30 11.32
12.40 11.40
12.50 11.55
12.60 11.62
12.70 11.69
12.80 11.74
12.90 11.78
13.20 11.82
13.40 11.85
13.60 11.89
14.10 11.95
15.00 12.00

Use the initial pH of the acetic acid solution to find the initial [H3O+] and initial [CH3COO-].

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