GHS Honors Chemistry
Acid-Base Titration Lab
Name: ____________________________________ Date: _______ Block: _______
PURPOSE: To determine the concentration of a solution of hydrochloric acid by acidbase titration.
INTRODUCTION:
Titration is a laboratory technique by which we can determine the
concentration of an unknown solution using a standard (known)
concentration of another solution that chemically reacts with the
unknown. This standard solution is called the titrant. We will also
need a way to know that the reaction between the unknown solution,
and the standard solution, is complete. In acid/base titrations, an
indicator, much like those that you have already seen in the lab, are
used. When the indicator changes color (colorless to pink, or vice
versa), this indicates that the equivalence point is reached. At the end
point:
Ntitrant x Vtitrant = Nunknown x Vunknown
In an Acid/Base titration, the Normality (N) is simply:
N=Mxn
where M = the Molarity of the solution, and n = times the number of or equivalents (the #
of H+ or OH- ions that dissociate from the acid or base).
For example:




HCl contains only one H+, so n = 1, and the Normality (N) = the
Molarity (M)
H2SO4 contains two H+, so n = 2, and the Normality (N) = 2 x M
NaOH contains only one OH-, so n = 1, and the Normality (N) = 1 x M
Ca(OH)2 contains two OH-, so n = 2, and the Normality (N) = 2 x M
The calculation for an Acid/Base Titration can be reduced to the following:
nAcid x MAcid x VAcid = nBase x MBase X VBase
In this experiment you will titrate a measured volume of HCl with a solution of NaOH of
known concentration. The acid and the base react with one another according to the
equation:
HCl (aq) + NaOH (aq)  NaCl (aq) + H2O (l)
The HCl is placed in an Erlenmeyer flask, and phenolphthalein indicator is added. The
NaOH solution is added from a buret into the flask containing the acid. During the first
stages of the titration, the NaOH will be completely neutralized, and an excess of acid
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GHS Honors Chemistry
Acid-Base Titration Lab
Name: ____________________________________ Date: _______ Block: _______
will remain. However, eventually there will be a point, the theoretical endpoint, at which
the acid and the base have neutralized one another exactly, and no more base should
be added to the flask.
The phenolphthalein indicator is used to determine experimentally the point, called the
experimental endpoint, at which the base has neutralized the acid. Phenolphthalein is
colorless in acid solution. It turns pink when the acid is completely neutralized and a
slight excess of base is present. In this titration, a successful endpoint is achieved if one
drop of base turns the solution in the flask from colorless to pink.
In this experiment, you can use separate burets for the acid and the base. It is
advantageous to use two burets. If you should overshoot the endpoint by adding too
much base, you will be able to add an additional measured volume of acid from the acid
buret. The additional acid will neutralize the excess base, and you can then add more
base to reach a new endpoint.
In this Acid/Base titration, both NaOH and HCl contain only one OH- and H+ respectively,
so for each, the number of equivalents (n) = 1. Since you will know or measure:

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MNaOH: the concentration of the NaOH solution in moles/liter
LNaOH: the volume in mL of NaOH used (which you can convert to L)
LHCl: the volume in mL of HCl placed in the Erlenmeyer flask
you can calculate the molarity of the HCl solution (MHCl):
MNaOH x VNaOH = MHCl x VHCl
MHCl = ( MNaOH x VNaOH ) / VHCl
For example, if 25.0 mL of 0.200 M NaOH is able to neutralize 30.0 mL HCl, we can
calculate the concentration of the acid solution:
MHCl = (0.200 M NaOH x 0.0250 L NaOH) / 0.0300L HCl
MHCl = 0.167 M
MATERIALS:
o
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2 -150 mL beakers
2 - 50 mL burets
double buret clamp
ring stand
250 mL Erlenmeyer flask
2 - 250 mL beakers
standardized solution of NaOH
Phenolphthalein indicator
o Unknown solution of HCl
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GHS Honors Chemistry
Acid-Base Titration Lab
Name: ____________________________________ Date: _______ Block: _______
PROCEDURE:
A. Record all your experimental data in the table.
DATA TABLE
MEASUREMENTS
#1
#2
#3
Concentration of NaOH
_______mol/L
________mol/L
_______mol/L
Initial reading of base buret
________ mL
________ mL
________ mL
Final reading of base buret
________ mL
________ mL
________ mL
Volume of NaOH used
________ mL
________ mL
________ mL
Initial reading of acid buret
________ mL
________ mL
________ mL
Final reading of acid buret
________ mL
________ mL
________ mL
Volume of HCl used
________ mL
________ mL
________ mL
B. Obtain about 120 mL of HCl solution in a 150 mL beaker. Label the beaker.
C. Rinse one buret with approximately 10 mL of the HCl solution, and let the liquid
drain through the buret tip into an empty 250 mL "waste" beaker. Repeat this
procedure twice more, using new 10 mL samples of HCl solution each time.
D. Refill the buret so that the meniscus of the solution is above the 0 mL mark.
Position the buret in a double buret clamp on a ring stand. Let some of the
solution run rapidly from the buret to expel all air bubbles from the tip and to bring
the level of the solution down to the calibrated region of the buret. If there is a
drop of solution hanging on the tip of the buret, remove it by touching the drop to
the inside wall of the 250 mL beaker.
E. Hold a piece of white paper behind the meniscus, and read the initial volume of
the solution at the bottom of the meniscus. Your eye must be at the same level
as the meniscus.
F. Obtain approximately 120 mL of NaOH in a second labeled 150 mL beaker.
Obtain a second buret and repeat Parts C to E, using the HCl.
G. Let approximately 20 mL of HCl to flow from the acid buret into a clean 250 mL
Erlenmeyer flask. Add two drops of phenolphthalein.
H. Place the Erlenmeyer flask under the tip of the base buret. A piece of white paper
placed under the flask will make it easier to see the color changes. While
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GHS Honors Chemistry
Acid-Base Titration Lab
Name: ____________________________________ Date: _______ Block: _______
continuously swirling the flask to ensure thorough mixing, run in the NaOH
solution from the buret. Initially, a pink color will appear at the point where the
NaOH comes in contact with the solution in the flask; however, this color
disappears quickly. As the endpoint nears, the color will disappear more slowly.
Eventually, the NaOH should be added drop by drop until one drop turns the
entire solution in the flask pink. This pink color should remain at least 15 seconds
while the solution is being swirled.
I.
If you overshoot the endpoint, add more acid from the acid buret until the solution
becomes colorless again. Then add the NaOH from the base buret until you have
the faint pink endpoint. When you have reached a satisfactory endpoint, read the
final volume of each buret.
J. Refill each buret and repeat Parts G to I twice more, using clean Erlenmeyer
flasks.
QUESTIONS:
1. Determine the concentration MHCl obtained from each titration. Then average the
results.
2. If 27.31 mL of 0.2115 M NaOH is able to neutralize 37.45 mL of HCl, what is the
concentration of the acid?
3. What volume of 0.117 M HCl is needed to neutralize 28.67 mL of 0.137 M KOH?
4. Why does the pink color, which forms at the point where the NaOH comes into
contact with the solution in the flask, disappear more slowly near the endpoint?
5. Why is it a good idea to carry out titrations in triplicate?
6. Why might you be told to use distilled water to wash a drop of solution adhering
to one of the buret tips into the Erlenmeyer flask?
7. Would the addition of several milliliters of distilled water to the Erlenmeyer flask
during the titration affect the results of the titration? Explain your answer.
8. If 35.93 mL of 0.1590 M NaOH neutralizes 27.48 mL of sulfuric acid (H2SO4),
what is the M H2SO4?
Modified from:
Whitman, R.L. et al. Chemistry Today 1: Laboratory Manual. 1989. Prentice-Hall Canada
Inc.,: Scarborough.
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