Volumetric Titration Lab
Objectives
 To practice using volumetric pipets and burets.
 To prepare and standardize a sodium hydroxide solution.
 To determine the molarity of a vinegar solution by volumetric titration with a standard base solution.
Procedure – Wear safety glasses at all times during this lab; NaOH will burn skin & eyes. Report any spills or if you get
the NaOH on your skin.
A sodium hydroxide (NaOH) solution has been prepared for you that is approximately 0.1 M. It is located in the large
carboy (plastic jug) on the cart at the front of the room. Be careful to not spill any of the corrosive NaOH solution on
the floor.
(Parts 1a-1f should be finished in no more than 2 class periods.)
1. Standardize your NaOH solution.
a) Obtain the following: Buret & buret clamp
ring stand
a clean 125-ml Erlenmeyer flask
phenolphthalein indicator
funnel
b) Prepare your buret. ONLY if your buret is dirty: clean your buret using a long-handled buret brush with a
single drop of dish detergent and lots of rinse water. Drain the buret completely.
Whether your buret is dirty or not: rinse the walls of your buret with about 10 mLs of your NaOH solution.
Discard this NaOH rinse down the drain. Do this step only at the beginning of each day, not every time you
use the buret.
c) Determine the mass of KHP (potassium hydrogen phthalate; KHC8H4O4) needed to react with 25 ml of your
approximately 0.1 M NaOH solution. The reaction is KHC8H4O4 + NaOH
NaKC8H4O4 + H2O.
Check with Mr. Smith to verify your calculation before you go on.
d) Setting up your Erlenmeyer flask. Add the KHP to a clean flask, recording the KHP mass to the nearest
0.0001 grams. Add about 20-25 mL of water and 3 drops of phenolphthalein. Swirl the liquid to dissolve the
KHP. You do not need to use a graduated cylinder to add the water, just squirt some in from a squirt bottle.
e) You are now ready to titrate! Fill buret to the top line (0.00 ml) and record the exact starting volume in the data
table, to the nearest 0.01 ml. Place your flask on a sheet of white paper under the tip of your buret. Barely
open the valve to drip NaOH solution into the Erlenmeyer flask containing KHP. Add base slowly until you
reach the first permanent pale pink color. Record the final volume to the nearest 0.01 ml in the data table.
f) Repeat parts d & e two additional times. Calculate the molarity of the NaOH solution in each trial. Average
your three trials. This number should be the exact molarity of your solution. Show me your data before you
continue.
(Part 2 is meant to be accomplished in no more than 2 class periods.)
2. Finding the molar mass of an unknown solid acid.
a) Before you use your buret today, rinse it with 10 mLs of your standardized NaOH solution. Put this solution
down the drain.
b) Refill your buret to the 0.00 mL mark with your standardized base. Record the exact starting volume in the
data table.
c) Into your clean Erlenmeyer flask, weigh the mass of the unknown solid acid that you have been assigned.
Record the exact mass of the unknown acid to the nearest 0.0001 grams. Add 20-25 mLs of water (a
generous squirt from a squirt bottle) and swirl the flask until the solid is completely dissolved. Add 3 drops of
phenolphthalein. Titrate until you reach the final pale pink color that doesn’t fade within ~10 seconds. Record
the exact ending volume in the data table.
d) Repeat steps b & c twice.
e) Calculate the moles of acid present in the flask from the moles of NaOH that were used to neutralize it.
f) Calculate the molar mass of the solid unknown acid by dividing the mass of the acid by the moles of acid.
Name
(1 pt)
Lab Partner
(1 pt)
Date:
(1 pt)
/ 81 pts
Data and Calculations: [6 pts – masses recorded to 0.0001 gram accuracy;
6 pts – volumes recorded to 0.01 mLs accuracy;
6 pts – moles, molarities, molar masses calculated with correct sig. figs. throughout the lab.]
Standardization of NaOH Data Table:
Trial 1
Trial 2
Trial 3
(Trial 4 only if needed)
Grams of KHP:
Moles of KHP:
(molar mass 204 g/mol)
(3 pts)
Moles of NaOH:
(same as moles of KHP)
Starting Volume:
(should be about 0.00 mLs)
Ending Volume:
(should be about 25.00 mLs)
Volume Used:
(difference between 2 previous lines)
(3 pts)
Molarity of NaOH:
(6 pts)
Average Molarity of NaOH:
(1 pt)
Your unknown number:
(1 pt)
Mole Ratio:
Use about this many grams for each titration:
1/
(1 pt)
g
Titration of Unknown Solid Acid Data Table:
Trial 1
Trial 2
Grams of Unknown Acid:
Starting Volume NaOH:
(should be about 0.00 mLs)
Ending Volume NaOH:
Volume of NaOH used:
(difference between 2 previous lines)
(3 pts)
Moles NaOH used:
(6 pts)
Moles of Unknown Acid:
(moles of NaOH x mole ratio)
(3 pts)
Molar Mass of Unknown:
(Grams / Moles)
(9 pts)
Average Molar Mass of Unknown Acid:
(1 pt)
Trial 3
(Trial 4 only if needed)
Conclusion Questions:
1.) If your lab partner actually placed twice as much KHP in your flask as called for, but didn’t tell you, and you
standardized the base, would you calculate the molarity of the base to be twice what it truly was, or half of
what it truly was? (2 pts)
2.) Say that after you had determined the concentration of your base solution, your lab partner spilled some of it,
but covered up the mistake by adding more water. How would this affect the actual molarity of the base?
…the calculated molar mass of your unknown acid? (2 pts)
3.) Find out from the teacher what the chemical formula of your unknown solid acid was. Calculate the true
molar mass of your unknown. Calculate your % error. Show both calculations. (2 pts for true molar mass calculation done
correctly; 1 pt for % error calculation done correctly; 10 pts for accuracy. If you don’t calculate the % error, you lose the 10 accuracy pts also.)
4.) There are 3 sources of error in this experiment: the balance (mass of KHP and unknown acid), the buret
(volume of NaOH solution), and your ability to consistently judge a good endpoint. Unfortunately, this third
source is the greatest source of error.
a) What is the readability of the balance?
(1 pt)
grams
(Don’t ask me; I won’t tell you.)
b) Calculate the magnitude of error for the balance using the grams of KHP from Trial 1 in the first table.
Show your calculation. (2 pts) (Don’t ask me how to calculate a magnitude of error; you should know this by now.)
c) What is the readability of the buret?
(1 pt)
mLs
(Don’t ask me; I won’t tell you.)
d) Calculate the magnitude of error for the buret using the ‘volume used’ from Trial 1 in the first table.
Show your calculation. (2 pts)