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Offline Nathaniel

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Determineing Ka
« on: April 05, 2008, 02:00:07 PM »
My question is found in the Analysis section. Thanks experts!


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

Procedure:
1.   Record the molar concentration 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 two drops of phenolphthalein to the acid.
6.   Record the initial pH of the solution.
7.   Add 1.00 mL of NaOH from the burette to the Erlenmeyer until the pH reaches 5.00.  Record the volume to 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 phenolphthalein 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.


NaOH(ml)           pH
0.00           2.52
1.00           3.58
2.00           3.59
3.00           4.92
4.00           4.09
5.00           4.14
6.00           4.55
7.00           4.73
8.00           4.98
9.00           5.07
9.20           5.09
9.40           5.14
9.60           5.19
9.80           5.24
10.00           5.25
10.20           5.37
10.40           5.38
10.60           5.45
10.80           5.59
11.00           5.62
11.20           5.75
11.40           6.18
11.60           6.29
11.80           6.54
12.00           10.68
12.20           11.15
12.30           11.36
12.40           11.43
12.50           11.57
12.60           11.65
12.70           11.67
12.80           11.77
12.90           11.79
13.20           11.83
13.40           11.84
13.60           11.88
14.10           11.92
15.00           12.00


Analysis:
 Write the chemical equation for the neutralization reaction you observed

Offline Borek

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Re: Determineing Ka
« Reply #1 on: April 05, 2008, 02:09:34 PM »
Please read forum rules.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

Offline Nathaniel

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Re: Determineing Ka
« Reply #2 on: April 05, 2008, 02:15:25 PM »
Sorry about that.

My first choice would be HCl + NaOH --> NaCl + HOH

Offline Borek

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Re: Determineing Ka
« Reply #3 on: April 05, 2008, 02:22:42 PM »
Huh? Are we reading the same question?
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Offline sjb

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Re: Determineing Ka
« Reply #4 on: April 05, 2008, 02:26:34 PM »
Sorry about that.

My first choice would be HCl + NaOH --> NaCl + HOH

So the formula for acetic acid is HCl?

Not that it matters (that much) what it is, but it may cause difficulties later depending on further questions, if for instance you need to calculate molecular weights etc. Check the formula and try again.

http://www.google.com/search?q=acetic+acid

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