Name:
Acid Lab – 22 points
Period:
Purpose: 1. Titrate two brands of vinegar with 1 M solution of NaOH to determine the
molarity of the vinegar.
2. Use the molarity of the vinegar to determine the pH of the vinegar.
Introduction: Acetic Acid is CH
3
COOH and vinegar is simply acetic acid in water (Vinegar is the “street” name of acetic acid). Vinegar is a 5% solution of acetic acid in 95% water. This percentage is by mass . So, in 100 g of vinegar, 5 g of that is acetic acid and 95 g is water. Vinegar has the same density as water and so 100 mL of vinegar is also 100g.
Pre-Lab Questions (10 pts, must show work)
1. Assume you have 10 mL of vinegar, CH
3
COOH . How many grams of acetic acid are in the vinegar? (Read Introduction, Show work):
2. How many moles of acetic acid are in the 10 mL sample of vinegar?
(Show work)
3. Find the molarity of Acetic Acid (CH
3
COOH) in your 10 mL sample of vinegar.
Record this on your data table as the Molarity of Acetic Acid based on pre-experiment calculations. (Show work):
4. Write the balanced equation of acetic acid in water (remember it is in equilibrium). Also remember that all acid/base reactions have coefficients of ONE. Also remember to put in (l) and (aq) where necessary. Also remember to put in + and – charges when necessary. (Example: Acetic acid doesn’t have a + or – charge. But, after it loses it’s hydrogen atom to the water, it will obtain a – charge.)
Remember an Acid + Water = Conjugate Base + Hydronium
5. Write the K a
expression (using symbols from the balanced equation – no numbers!).

6. Show your work and find the theoretical pH of vinegar. To do this, a) Use the K a
expression you just wrote in #5. b) You have the concentration or molarity of acetic acid CH
3
COOH, which you found in question #3 c) The Given K a
for acetic acid is 1.8 x 10 -5 . d) Solve for [H + ]. e) Use pH= -log[H + ]. Once you have found the theoretical pH. Record this as THEORETICAL pH on your data table.
[H + ] =
[H + ] concentration (M) pH =
7. Write the balanced equation of acetic acid being mixed with NaOH . (remember it is in equilibrium). Also remember that all acid/base reactions have coefficients of ONE. Also remember to put in (l) and (aq) where necessary. Also, an
Acid + Base = a Salt + Water.
8. How many moles of NaOH are going to be required to neutralize the moles of acetic acid you determined in question #2? Hint: Don’t make it too hard by reading a lot into the question, the mole to mole ratio is 1:1
9. Assume you have a 1.00 M solution of NaOH. How many mL of this solution will it take to make the number of moles you determined you were going to need in question #8? Record this as Predicted volume of NaOH to be titrated in your data table. (Show work)
THIS IS VERY IMPORTANT: Your answer to #9 is a good approximation of how many mL of 1.00 M NaOH you will be titrating into your 10.0 mL sample of vinegar.
Procedure:
1. Use a graduated cylinder and measure 50.0 mL of 1.00 M NaOH. Fill your buret with the NaOH.
2. Use the plastic pipette in the beaker of Heinz Vinegar and measure 10.0 mL of vinegar into a graduated cylinder and then transfer it to a 250 mL Erlenmeyer flask.
3. Add only 2 drops of Phenolphthalein indicator to the 250 mL Erlenmeyer flask.
4. Place a magnetic stirbar in the Erlenmeyer flask. Turn on the magnetic stir plate so that it causes the stirbar to spin gently.
5. Begin to titrate the 1.00 M NaOH into the Erlenmeyer flask. Tips:

In your pre-lab, you predicted the amount of NaOH that should be delivered to neutralize the acid. Therefore, you should be able to go “fast” until about 5 mL or so before that point. Then, you’ll want to go dropwise – this will help prevent you from overshooting the amount.

When the Erlenmeyer remains “just a light hint of pink”, you are done. The trick is the Erlenmeyer is supposed to remain a light hint of pink and not turn back to clear.

"I overshot, the solution is DARK PINK. What do I do?" You can add another 5 mL of acid and continue to titrate. When you are finished, you’ll have to re-do your calculations to reflect the fact that you used 15 mL of acid instead of 10

6. When you are done titrating, record the volume of 1.00 M NaOH you titrated as Actual Volume of 1.00 M NaOH titrated to the flask on your data table
X: If time permits, repeat the experiment with Albertson’s vinegar to see if you get the same results. If you do, then you should purchase vinegar based on price.
In the space below, diagram and flowchart all pertinent steps of the procedure #1-6. Draw all necessary glassware, equipment, stands, etc. Use RED color to represent your acid. Use BLUE color to represent your base.
1 2 3
4 5 6
Calculations: (10 points)
1) You have most of the values for the data table from the pre lab alone. The only thing you have left to determine is the
Experimental value of Molarity for Acetic Acid Be sure you show your work for this calculation for both Heinz and
Albertson's vinegar before you enter the number in the data table below
Show Work: Experimental value of Molarity for Acetic Acid
Heinz Albertson's
Data Table
Volume (L) of vinegar in
Erlenmeyer Flask
Predicted volume (L) of 1.00 M
NaOH to be titrated to the flask
Actual Volume (L) of 1.00 M
NaOH titrated to the flask
Molarity (M) of Acetic Acid based on pre-experiment calculations (pre-lab question
#3)
Heinz Vinegar Albertson's Vinegar

Experimental value of Molarity
(M) for Acetic Acid
% Error in Molarity of Acid =
(|Experimental – Predicted value|) x 100
Predicted value
Questions: (10 points – minus one for every letter incorrect)
1. Is acetic acid a weak or a strong acid? Look in your notes if you don’t remember.
2. Finish this statement: The smaller the K a
, the _________ ( lower or higher ) the pH
3. Find the pH of the following molarities of HCl (remember it is a strong acid).
( this is not multiple choice, each letter is a separate question ) a. 1.0 x 10 -3 M b. 1.0 x 10 -5 M
4. Find the molarity of the following pH values for HCl (remember it is a strong acid).
( this is not multiple choice, each letter is a separate question )
a. 2
b. 4
5. Find the pH of the following molarities of acetic acid (remember it’s a weak acid with a
K a
= 1.8 x 10 -5 ).
( this is not multiple choice, each letter is a separate question ) a. 1.0 x 10 -3 M b. 1.0 x 10 -5 M
6. Find the molarity of the following pH values for acetic acid (remember it’s a weak acid).
( this is not multiple choice, each letter is a separate question ) a. 2 b. 4
What is due for this lab and in what order?
1. Pre-lab showing all calculations for each question (when a calculation is required)
(10 points)
2. Calculation for Molarity of Acetic Acid based on experiment. (if you only have time to do one brand, then there will be only one calculation. If you did two brands, then there will be two calculations).
Also, show your percentage error calculations for experimental molarity and calculated molarity (10 points)
3. Data Table (same thing: One brand = 1 data table. Two brands = 2 data tables) (must be included or – 2 points)
4. Questions. Make sure you show your work – especially on questions 5 & 6! (10 points)