LAB: Acid-Base Titration
Name_______________________________
Date_______________ Block____
Titration is a process that involves the reaction of a known amount of an acid solution having a
known concentration to determine the concentration of a base solution.
The “unknown” concentration of base in a solution is determined by carrying out a neutralization
reaction. An appropriate acid-base indicator solution is used to indicate that the neutralization is
complete. The steps in the titration process are as follows:
1. A measured amount of acid solution with known concentration is added to a flask.
The solution of known concentration is called the standard solution.
2. An appropriate indicator (such as phenolphthalein) is added to the acid solution in the flask.
3. Base of unknown concentration is added to the mixture of acid and indicator solution until a
color change is observed.
The addition of the base is carried out using a standard dropping bottle and counting the drops of
base that are added until the indicator shows that neutralization has occurred (a color change is
observed). In this lab, the indicator solution is phenolphthalein (PHTH) which is colorless in
solutions having a pH below 8.0 and pink in solutions having pH of 8.0 or greater.
Purpose: to determine the molar concentration of a sodium hydroxide solution by using a
solution of HCl(aq) of known molarity and an appropriate acid-base indicator solution.
Equipment and Materials:
per pair of students:
safety goggles and aprons
1 clean, dry 125-mL Erlenmeyer flask
standard dropper bottle containing 0.20 M HCl(aq) (standard solution)
standard dropper bottle containing NaOH(aq) of unknown concentration
standard dropper bottle containing DI H2O
per table:
standard dropper bottle containing phenolphthalein indicator solution (PHTH)
paper towels
access to bottle of saturated sodium bicarbonate solution to be used for acid spills
access to bottle of acetic acid solution (vinegar) to be used for base spills
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Procedure:
NOTE: standard dropping bottles deliver a volume of 20 drops/mL when inverted vertically.
Proper technique of using the dropper bottles is crucial to accurate results in this lab.
1. Carefully add exactly 10 drops 0.20 M HCl solution into the clean, dry 125-ml Erlenmeyer
flask.
2. Add exactly 10 drops DI H2O to the acid solution in the 125-mL Erlenmeyer flask.
3. Add 1 drop of the phenolphthalein indicator to the acid-DI water mixture in the flask.
4. Swirl the flask for about 15 seconds to thoroughly mix all solutions in flask.
5. Place a piece of plain white paper under the flask.
6. Begin the titration by adding the base solution to the solution in the 125-mL Erlenmeyer
flask ONE DROP AT A TIME.
SWIRL the contents of the flask for at least 15 seconds between each addition of base.
7. Continue adding the base one drop at a time UNTIL A FAINT PINK COLOR REMAINS
FOR ABOUT 30 SECONDS. Record the total number of drops of base that had been
added.
NOTE: If “over-titration” occurs, that is, the pink color is too deep, add acid solution – ONE
drop at a time, swirling the flask for about 30 seconds after each drop - until the color JUST
disappears; record the number of drops of acid solution that were added to the flask. Then add
the base solution carefully one drop at a time, swirling the flask for at least 15 seconds between
drops until the faint pink color appears. Record the number of drops of bases that were added.
8. Thoroughly rinse the flask with tap water. Then rinse the flask twice using a small amount of
DI water – add DI water and swirl the flask before emptying the water into the sink.
AIR DRY the flask by holding the flask over an AIR jet located at the side counters of the
room. Be careful to hold the flask firmly.
9. Repeat Steps 1-9 three more times for a total of four(4) trials.
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DATA TABLE
Titration of an Acid with a Base of Unknown Concentration
Trial
1
Substance
Used
HCl(aq)
Volume of Substance Volume Of
(units given)
DI H2O Added
10. drops
NaOH(aq)
2
HCl(aq)
drops
10. drops
NaOH(aq)
3
HCl(aq)
HCl(aq)
10. drops
drops
10. drops
NaOH(aq)
4
10. drops
10. drops
drops
10. drops
NaOH(aq)
10. drops
drops
Calculations (to be done in space provided on next page)
For each trial, calculate the molarity of the NaOH(aq) using the relationship:
MaVa =
MbVb
where Ma = molarity of the acid solution
Va = volume used of the acid solution in L
Mb = molarity of the base solution
Vb = volume used of the base solution in L
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Calculations of molarity of NaOH for each trial:
Trial 1:
Trial 2:
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Calculations of molarity of NaOH continued:
Trial 3:
Trial 4:
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Calculate the average molarity of the NaOH(aq) using your values from the four trials.
Conclusions and Additional Calculations (SHOW ALL WORK!!!!!!!)
1. How precise (reproducible) were the results of your 4 trials? Explain any factors that may
have affected your results.
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2. Your teacher will write the actual molarity of the NaOH(aq) on the board. Calculate your
percent error. % error = (experimental value – actual value) x 100
actual value
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