Objective:
The purpose of this lab is further understanding of acid/base equilibria through
experiments in buffer action and the use of acid/base reactions for analysis.
Procedure:
A. Buffers
1.
Calculate the number of moles of acetic acid in a 100 mL sample of vinegar and
it’s concentration in moles/L [M]. Data: MW=60, Ka=1.8x10
-5
, density=1.01
g/ml.
2.
Setup a TI/CBL2 with a pH sensor and calibrate with standard known buffers 4
and 7. Rinse with DI water between measurements and blot dry with Kimwipe.
3.
Make 2 samples of 100 ml of acetic acid buffer at pH 5 using these two methods:
a.
Add 3-5 drops universal indicator to 100 ml of commercial vinegar.
Calculate exact amount of solid sodium acetate trihydrate (MW=136.08)
that needs to be added to solution to make buffer of pH=5. Record pH.
b.
Divide 20 ml of commercial vinegar into two 10 ml portions. Add 3-4
drops phenolphthalein indicator to one of them. Add 1.0 M NaOH to this
one slowly until it turns light pink. Mix two solutions back together and
measure pH and record, then adjust to pH 5 by adding 6 M NaOH. Record
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- Fall '08
- Cox
- Mole, pH, Reaction, ml
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