EXPERIMENT
Volumetric Analysis
Standardization of an HCl Solution
PURPOSE
To determine the molarity of an unknown hydrochloric acid solution by acid-base titration using a
standard sodium hydroxide solution. The standardized acid solution will be used in determining the
formula of calcium hydroxide.
PROCEDURE
1. Obtain one 50 mL buret. Determine whether you have a clean buret or not. A clean buret will drain
freely without forming droplets on the inside surface. If your buret is clean go to step 2. Otherwise,
thoroughly clean your buret using a detergent solution and a long buret brush. Rinse the buret
thoroughly with tap water, and then once with distilled water, and allow to drain.
2. Examine the functioning of the stopcock. See that it turns freely to deliver a full stream of water
and that it does not leak.
3. Rinse the buret with an approximately 5 mL portion of the standard NaOH solution (~.1M), making
sure that you discard this rinsing solution. Record the concentration of this NaOH solution in your lab
notebook. Repeat this rinsing process with another 5 mL portion of the standard NaOH. Run at least a
portion of each rinse through the stopcock and tip so that all parts of the inside of the buret will have
come in contact with the NaOH solution.
4. Fill the buret with the standard NaOH solution above the 0 mL mark. Allow the solution to drain out
through the stopcock and tip to insure that any trapped air bubbles are completely removed. Refill to
buret if necessary. The liquid level may be stopped at any point at or below the 0.00 mL mark. Close the
air passage to the NaOH solution by placing an inverted 50 mL test-tube on the top of the buret.
5. Prepare 200 mL of an approximately 0.1 M HCl solution, in a 250 mL Erlenmeyer, by diluting the
required amount of a Stock 6M HCl solution. Determine the volume of the concentrated HCl solution
required to produce the desired concentration by dilution (M1V1=M2V2). Pour the required volume of
the concentrated solution into a clean 250 mL Erlenmeyer. Add distilled water, mix thoroughly and
bring volume to the 200 mL mark on the flask. Cork the flask and mix by inverting several times.
Rinse a 150 mL beaker with a small amount of your HCl solution, and discard the rinse solution. Pour
about 50 mL of your approximate 0.1 M HCl solution to be standardized into the 150 mL beaker. Use a
10 mL Mohr pipet and deliver 10.00 or 15.00 mL of the acid solution to a clean 125 mL Erlenmeyer
flask. Add enough distilled water (easier to visualize end-point) to bring the volume to the 50 mL mark
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of your EF and two to three drops of phenolphthalein indicator solution. Place a piece of white paper
beneath the flask (This will help you see the end point more clearly.) Before you begin the titration
record the initial volume of NaOH (titrant) in your notebook. To begin titrating the acid with the
NaOH, open the stopcock of the buret almost all of the way and stir the solution by swirling the flask
(Figure 1). As the end point is approached, the faint pink color existing in parts of the unmixed acid
solution will persist for several seconds. At this point, you must decrease the rate of addition of NaOH
until you are adding drops one at a time and thoroughly mixing the solution before adding the next drop.
As you develop your skill, you will be able to approach the end point so slowly that you will be able to
touch the tip of the buret to the inside of the flask and add fractional drops that can then be rinsed down
into the solution with distilled water. The end point is reached when a faint pink color persists
throughout the solution after it has been swirled. If the pink color fades after the solution has been
standing, it will be because carbon dioxide has been absorbed.
6. If you have the misfortune to go past the endpoint by more than 1 drop, add enough additional acid
(record added volume) to remove the pink color. Then continue the titration with the NaOH, adding the
base more slowly this time.
7. Read and record the final buret reading for each solution.
8. Repeat the titration two more times.
9. Calculate the molarity of the HCl solution for the three titrations. These molarities should agree to
within 2 %. If they don't, consult the instructor. The unknown HCl solution has now been standardized.
10. Discard the remainder of this standardized HCl solution into a designated container.
).
Figure 1.
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Name ____________________________
LAB
REPORT
Section _________ Date _____________
Volumetric Analysis:
Standardization of an
HCl Solution
Instructor _________________________
Titration Results.
Trial 1
Trial 2
Trial 3
Volume of HCl
(pipet) used
=
mL
mL
mL
NaOH Buret
2nd reading
=
mL
mL
mL
1st reading
=
mL
mL
mL
Volume of NaOH solution used
=
mL
mL
mL
Molarity of NaOH =
M
///////////////////////////
///////////////////////////
///////////////////////////
Molarity of HCl
(Show sample calculation below)
=
M
M
M
Average Molarity of HCl
=
M
Relative deviation (ppt)
(Show Sample Calculations below) =
=
In the relative error formula xi is the value of the molarity obtained for a given trial; x is the average
molarity; n is the total number of trials.
Calculations: (Show a sample calculation of each unique type of determination for full credit.)
Problems: (Show all calculations to obtain full credit.)
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1. 24.60 mL of 0.185 M HNO3 are titrated with 27.35 mL of a KOH solution. What is the molarity of the
KOH?
2. 0.280 gram of KOH will just neutralize what volume of 0.200 M H2SO4?
3. 0.750 gram of a sample of commercial lye is dissolved in water and titrated with 32.00 mL of
0.500 M HCI. What is the percent purity (the active ingredient in Lye is NaOH) of this sample?
4. A 0.345 gram sample of oxalic acid dihydrate crystals (H2C2O4·2 H2O) is dissolved in water and
titrated with 24.50 mL of a sodium hydroxide solution. What is the molarity of the NaOH?
5. 80.0 mL of 0.200 M NaOH is mixed with 20.0 mL of 0.600 M HCl. What is the concentration of the
remaining OH-? (Final volume is 100.0 mL.)
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