Lab: Titration of Household Ammonia and Vinegar Name:________________
Background: Often times, the concentration of a basic or acidic solution is
unknown. A laboratory technique known as a titration allows chemists to determine
the concentration of a solution. In this technique, a solution of known
concentration is used to determine the concentration of an unknown solution, using
the properties of acids and bases. An indicator is used to determine the pH of the
solution during the process. In this lab, phenolphthalein will used. Phenolphthalein
is colorless in acidic solutions and turns pink in basic solutions.
Purpose: In this lab you will determine the actual amount of ammonia that is in
household ammonia, and the amount of acetic acid that is in vinegar. Or, how much
of these solutions are actually just water!
Prelab Questions:
1) Finish the equation for ammonia reacting with water:
NH3 + H2O
__________________
2) Finish the equation for acetic acid dissociating in water.
CH3COOH
H2O
________________
3) a. What color should the phenolphthalein turn in ammonia? _____________
b. What color in the acetic acid? _______________
Procedure:
Part I: Titration of Ammonia
1) Position a 50 ml beaker over a white background.
2) Place 7 drops of household ammonia water into the beaker.
3) Add 1-2 drops of phenolphthalein indicator to the ammonia.
4) Count the number of drops of 0.10M HCl it takes to make the solution colorless.
Make sure you add the acid SLOWLY as you near the "end point" by adding one
drop at a time and stirring with a tooth pick.
# of drops: ______________
Calculation the concentration of NH3:
[HCl] = 0.10M
Volume = ______ drops
[NH3] = ?
Volume of NH3 = 7 drops
[NH3] = (0.10) (_____ drops)
= _________ mol/l
7 drops
Calculate percent concentration:
[NH3] X 17g/mol X 100%
1000g/l
[NH3] = _______%
Calculate the percent water:
100% - _______% NH3 = _______% water
Part II: Titration of Vinegar:
1) Position a 50 ml beaker over a white background.
2) Place 5 drops of vinegar into the beaker and add 1-2 drops of phenolphthalein.
3) Count the number of drops of 0.20M NaOH it takes to make the solution turn a
pale pink.
4) Record the number of drops it takes: _________ drops NaOH
Calculations:
[NaOH] = 0.20M
Volume = ______ drops
[CH3COOH] = ?
Volume of CH3COOH = 5 drops
[CH3COOH] = (0.20) (_____ drops) = _________ mol/l
5 drops
Calculate percent concentration:
[CH3COOH] X 60g/mol X 100%
1000g/l
[CH3COOH] = _______%
Calculate the percent water:
100% - _______% CH3COOH = _______% water
Analysis: How close were your calculations to the actual percent composition on
the label? Calculate your percent error.