Name
Period_
Lab – Titration of Acids and Bases
Introduction:
Titration is a way to determine concentration of a solution by measuring the volume of that solution needed to react completely
with a volume of a solution of known concentration. We will conduct two types of titrations.
In the titration 1, you will add a known concentration solution – the titrant - to a measured quantity of the solution of unknown
concentration - the analyte - until equivalent amounts (or moles) of hydrogen ion from the acid and hydroxide ions from the
base have been combined to form a salt and water. This point in a titration is called equivalence. At the equivalence point all that
remains is water and a salt, theoretically. To witness equivalence, you will choose an indicator that changes color at or near the
equivalence value. Indicators change color at a particular pH, called endpoint. It is desirable for endpoint to be near the predicted
equivalence for a neutralization reaction. You will be allowed to select your indicator for the first titration.
In titration 2, you will create a titration curve with your group which will serve as a study tool for all Pre-AP Chemistry students.
We will compare 4 different types of titration! Using a pH probe and carefully logging volumes and pH, you will collect data
and enter it into a google sheet. The sheet will compile data and graph the curve for 1 of the 4 titration types and the data will be
synced in Canvas for study and evaluation.
Materials:
beakers
ring stands
flasks
buret clamps
distilled water
wash bottle
burets
hydrochloric acid
acetic acid
sodium hydroxide
various indicators
pH probe
ammonia
funnels
Safety: Wear safety goggles. An apron is recommended. Follow all instructions. Safety data sheets for all chemicals used in this lab
are available in the room.
Pre-Lab Questions:
1) Write the complete molecular AND net-ionic equations for the neutralization of sodium hydroxide with hydrochloric acid.
2) How would the net-ionic equation differ if hydrofluoric acid were used?
3) At equivalence point in any titration, what substances remain in the reaction vessel (ignore water)?
4) The concentration of a hydrochloric acid titrant is 0.25M. What pH is the acid? What is the pOH?
5) Sketch a strong acid solution being titrated with a strong base. Be sure to label the axes of your graph.
TITRATION 1 Procedure (use procedure when instructed):
1. At your station are a magnetic stirrer, a stirring bar, a flask, and a wash bottle of distilled water.
2. The apparatus at right is the intended setup. A ring stand holds clamp that holds a buret of your
titrant, NaOH or HCl. Unknown analyte solutions will be assigned to you.
3. Retrieve assigned volume of the analyte acid samples into your flask.
4. Create a data table for the titration. Record unknown ID, indicator chosen, beginning and
ending base buret volumes, acid volume used, molarity of titrant, and your observations from
the titration.
5. Record the start volume of the titrant buret to the nearest 0.01 mL, in the data chart you created.
6. Add two or three drops of the indicator you have chosen to the flask. Indicator information is below.
Swirl to mix the solution. Record observations.
7. Insert stir magnet into flask carefully by sliding it down the side wall of the flask. Place flask on
stirrer, turn knob until the stirrer is rotating about 2-3 times per second.
8. SLOWLY add titrant dropwise until endpoint is reached. Wash your flask walls with the wash
bottle to move any resting titrant into the solution.
9. Monitor your progress dutifully and IF you over-titrate, you may add back analyte from stock burets
at the front of the room 1.00mL at a time (not drops).
10. Monitor titrant volume! IF you empty the titrant buret, you cannot measure and must start over.
Ensure you start with adequate volume.
11. When you reach equivalence, ask your teacher to approve the color of the endpoint.
12. Record data and calculate unknown molarity!
13. Pour flask waste down the drain carefully and follow with tap water. Save the magnet! Rinse the
flask twice with tap water and once with distilled water from the wash bottle and repeat with another
unknown and indicator!
Indicator
Phenolphthalein
Bromothymol blue
Methyl red
Color < endpoint
Colorless
Yellow
Red
Endpoint Color
Light Pink
Green
Orange
Color > endpoint
Deep Pink Red
Blue
Yellow
Endpoint pH range
8.2-10.2
6.0-7.6
4.4-6.2
TITRATION 2 Procedure (use procedure when instructed): YOUR TITRATION ______ (A, B, C or D)
1.
2.
3.
4.
5.
6.
7.
8.
9.
Identify your acid and base and their respective concentrations on page 3.
Set up your Labquest or TI lab cradle. The pH probes are fragile, be careful. If the setup
does not operate properly, consult your teacher immediately.
As in the diagram at right, set up your buret and beaker with stirrer inside and pH meter
clamped to your stand.
Slowly titrate adding 0.50 mL or less dropwise and checking pH at each interval. You
may take more data points but do NOT take fewer! The goal is to get a clear titration
curve!
Add titrant dropwise by these small volumes until an acidic solution has become basic or
vice versa. This is important because it gives you a view of the whole titration curve.
Each team member should have all the data for this titration.
Your teacher will give you instructions for sharing your data via Google Sheets.
The data should be entered by the following date and
time____________________________________.
You will use the data to draw and compare all 4 types of titration.
TITRATION 1
LEGIBILITY and ORGANIZATION impact your score!
Titrant formula and molarity ______________
Indicator _________________________
Analyte formula __________________________
DAY 1 – TITRATE TO EQUIVALENCE –titrant – an acid or base of known concentration titrated into your unknown analyte.
1. Write the balanced reaction.
2.
At what pH do you expect equivalence to take place? Choose your indicator accordingly!
3.
4.
5.
6.
Make observations and collect data below. Include indicator chosen and analyte ID.
Perform at least 2 titrations, but do as many as you can! SHOW WORK for calculations.
Write the balanced chemical equation.
Calculate an average molarity for the analyte solution you tested. SHOW WORK!
TITRATION 2 – CREATE A TITRATION CURVE.
Acid ____________
Base______________
1.
2.
3.
You will be assigned to a titration. (A: SA & SB, B: SB & SA, C: SA & WB, D: SB & WA)
Identify your acid and base and their respective concentrations above.
At what about pH do you expect equivalence?
4.
Collect data below. Minimum intervals should be 0.5ml but can be smaller. Upon completion, you may enter your data via
the Google sheet. Your teacher will provide instructions. You will need to access this data to complete the lab.
Post Lab Questions
1) In titration 1, why is it acceptable to wash the flask with distilled water to move reagents from the flask walls to the solution?
2) Would you rather titrate with 20mL of analyte or 10 drops? Why?
3) Calculate the number of hydronium ions in one drop of 0.25M HCl. 1mL contains 20 drops of the solution.
4) Using the data collected via the online Google Sheets, sketch and label each type of titration. Label axes and place a visible
DOT at the approximate equivalence point.
5) Propose what the titration curve of a weak acid by a weak base might look like. Label axes.