Titration Lab
Introduction:
One of the most common and familiar reactions in chemistry is the reaction between an acid and a base. This
reaction is called neutralization.
HAaq) + BOH(aq)  H2O(l) + BA
In this experiment you will use this reaction to determine accurately the concentration of several different acids.
You will determine the amount of acid using a base in a process called titration.
An indicator solution is used to determine when the acid has exactly neutralized the base, or vice versa. A
suitable indicator is one that changes color when equivalent amounts of acid and base are present. The color change is
called the end point of the titration. In this lab, we will use phenolphthalein as an indicator which turns pink at a pH of
approximately 9.
Purpose:
To identify the concentration of three acids using a base of known concentration. The three acids are H3PO4, H2SO4 and
HCl.
Safety:
Acids and bases are corrosive. Use appropriate PPE. Make sure the stopcock is closed before filling the buret. Watch the
following video for proper titration technique.
http://www.youtube.com/watch?v=9DkB82xLvNE&feature=related
Procedure:
1. Accurately measure about 25 ml of H3PO4 solution. This means pour about 25ml in a graduated cylinder and
then accurately read the volume of the graduated cylinder to the tenths place. Record the volume of the acid.
Transfer the acid to an Erlenmeyer flask and add 2 drops of indicator to the acid solution. Add phenolphthalein
to the HCl and H2SO4. Add methyl orange to the H3PO4.
2. Read the initial volume of the buret. Note that the markings indicate the volume of the .500M NaOH
delivered from the buret.
3. Titrate to the endpoint. Add .500M NaOH slowly while swirling. Color will change and then disappear
until the endpoint is close. Add drops one by one until a persistent faint color is obtained. Record the final
volume of the buret.
4. Repeat procedures 1-3 using H2SO4 and then HCl.
Data:
H3PO4
Volume of Acid (ml)
Volume of Buret before
titration
Volume of Buret after
titration
Volume of .500M NaOH
used in titration
H2SO4
HCl
Calculations:
Using the formula in your acid and base reaction notes, calculate the concentration of each of the acids titrated.
Questions:
Consider each of the following potential sources of error. Answer:
“H” if it would have caused your calculated value for Molarity of NaOH to come out too high
“L” if it would have caused it to come out too low.
“N” if it would have no effect on your value.
a. There was a little distilled water in the Erlenmeyer flask before you began the titration.
b. There was a little HCl in the Erlenmeyer flask before you began your titration.
c. You added 3 drops of phenolphthalein, instead of 2 drops.
d. An air bubble was present in the NaOH buret, but it stayed in while you titrated.
e. An air bubble was present in the NaOH buret, and it came out in the middle of your titration.
f. While you were titrating, some NaOH dripped onto the table, instead of into the flask.
g. You forgot to add the phenolphthalein indicator.
Conclusion: State results, recap procedure, talk about sources of error.