Cora Burt & Julie Wasylnka
Chemical Analysis: Calcium Content of Common Liquids
(lab adapted from a UTS resource, author unknown)
Introduction:
Chemical analysts conduct quantitative tests to identify unknown chemicals, determine their composition, and
measure their physical and chemical properties. You are already familiar with acid-base titration techniques,
and how they may be used to determine concentrations, but you may not know about EDTA titrations. EDTA
(ethylenediaminetetraacetic acid) is a chelating agent that bonds with ions like Ca2+ (aq) to form complex ions.
Calcium is a chief cause of water hardness. EDTA molecules bind hard-water ions, removing them from
solution. A common indicator used in EDTA titrations is eriochrome black T (EBT), which changes from pink to
blue at a single endpoint, when all calcium ions have reacted with EDTA. EDTA titrations must be
performed at a pH of approximately 10. An ammonia/ammonium chloride buffer is used to maintain the
correct pH throughout the titration.
Task
You will be a chemical analyst. Over a period of two weeks, you will apply concepts, lab skills, and problemsolving skills learned in this unit to determine the concentrations of Ca2+ solutes in a calcium containing
solution of your choice, with approval by the teacher.
Day 1:
Pre-lab Questions (DUE DATE: _______________________________)
1. Identify a calcium containing solution to test ___________________________ [Teacher initials ____]
2. For a second test sample, identify a method to change the [Ca2+]
__________________________________________________________ [Teacher initials ____]
Prediction:
3. Predict how the [Ca2+] will differ after the experimental sample has been altered. This must be included in
your final report.
Cora Burt & Julie Wasylnka
Day 2:
Experimental Design:
The [Ca2+] of two identical aqueous samples is determined by performing EDTA titrations in a pH 10
ammonia/ammonium chloride buffer using EBT indicator. One sample is titrated “as is” which is the control.
The other sample is first subjected to conditions (of your design) that change the [Ca2+] in a predictable way.
This is the experimental sample.
Planning & Test Run (DUE DATE: _____________________________)
Materials Provided:
• 120 mL EDTA solution
• 2 x 60 mL samples of a test solution
• 30 mL pH 10 ammonia/ammonium chloride buffer
• Eriochrome black T indicator in dropper bottle
• beaker
• volumetric pipette/pipette bulb
• distilled water in wash bottle
• Erlenmeyer flask
• Buret
• Ring stand clamp
• white sheet of paper
• graduated cylinder
1. List the additional materials that you will require to modify your experimental sample. All of the materials
utilized must be included in your final report.
2. Plan and write a procedure for modifying the [Ca2+] of the sample. Teacher approval must be obtained prior
to preparing your test samples and executing the EDTA titration. [Teacher initials ____]
3. Execute your procedure and perform a test run of the EDTA titration. Remember to add 4 mL of pH 10
buffer and 3 drops of EBT indicator solution to titrating flask.
 take note of any issues you encountered which may need to be modified before the final test run
Day 3:
EDTA Titration Execution Date: _____________________________________
Day 4:
Analysis (DUE DATE: ________________________________)
1. Describe the equilibria and the changes they undergo as the EDTA titration progresses.
(Recall the overall reaction: Ca2+ + EDTA  CaEDTA)
2. Use your evidence to calculate [Ca2+] of your two samples.
3. Answer the following questions:
a) Compare an EDTA titration and an acid-base titration
b) What are some commercial and pharmaceutical uses for EDTA? Name three products you can purchase
at a grocery store or pharmacy that contain EDTA and explain why EDTA is added to the product.
c) Is EDTA safe? Describe safety considerations associated with the use of EDTA as a laboratory reagent
and as a consumable product.
Evaluation: Marking rubric is attached
/24 I
/4 C
/ 8A
Cora Burt & Julie Wasylnka
Chemical Analysis: Calcium Content of Common Liquids Checklist
1. I have a chosen a variable from the given list which will alter [Ca2+] in my experiment _____
2. In our research, we have used Science Resource center database and have
found
at least one reputable websites
at least one newspaper/magazine source
______
______
3. I have consulted the marking scheme when doing my research
______
4. My procedure is written up. I have included references in my notes
______
5. I have asked the teacher any questions I have about the procedure
______
6. The teacher has checked my procedure (and signed off below)
______
7.
I have made the modifications to my procedure as indicated in the teacher’s
feedback
______
8. On the practice day, I have noted any refinements that need to be considered
in my final submission.
9. On the day of the task, I have consulted my lab partner on how we will be
dividing the work.
Write your materials here:
Write your stepwise procedure here:
Teacher’s Signature for Procedure
______
Cora Burt & Julie Wasylnka
Rubric: Chemical Analysis: Calcium Content of Common Liquids (Modified from http://www.ntci.on.ca/departments/chem/labreportrubric.pdf)
Level 1
Level 2
Level 3
Level 4
NI
S
G
E
NI
S
G
E
NI
S
G
E
NI
S
G
E
NI
S
G
E
Grade
Part 1: Learning Skills
In-Class work time used
effectively to complete the
task
Devises and follows a plan
and process for completing
work and tasks
Accepts various roles and an
equitable share of work in a
group;
Demonstrates curiosity and
interest in learning
Completes and submits class
work on time
N/A
N/A
N/A
N/A
Part 2: Assignment
Initiating
Hypothesis
Has some difficulty
generating a hypothesis
or prediction
Planning
Materials, Design and
Procedure
Final product does not
discuss experimental
materials that were used in
the experiment. Summary
of the procedure is not
present or is poorly
conveyed.
Performing and Recording
Analysing and Interpreting
Generates a
hypothesis or prediction
with some degree of
effectiveness
Some materials are
identified; discusses the
procedure briefly and/or is
missing several steps.
Generates a valid
hypothesis or prediction
with considerable
effectiveness
Most materials used are
Identified. A concise
summary of what was done
in the experiment was
outlined.
Another student should be
able to reproduce the
procedure.
Generates an
insightful hypothesis or
prediction with a high degree
of effectiveness
All materials used are
identified.
Presented a clear and
concise summary of all steps
in the experiment.
Another student would easily
replicate the experiment by
following the procedure.
4I
Titrations are performed
with limited accuracy;
limited care was taken with
equipment and reagents
Titrations are performed
with some accuracy; some
care was taken with
equipment and reagents
Titrations are performed with a
high degree of accuracy;
extreme care was taken with
equipment and reagents
8I
Records little or no data.
Records data but
organization is lacking
Draws conclusions based
on the data with some
effectiveness
Records and displays data in
an organized and
skillful way
Draws conclusions based on
the data with a high degree of
effectiveness
4C
Draws conclusions based
on the data with limited
effectiveness
Titrations are performed
with a considerable degree
of accuracy; care was taken
with equipment and
reagents
Records relevant
data in an organized
way
Draws conclusions based
on the data with
considerable effectiveness
Addresses a limited number
of the analysis
Addresses some of the
analysis
Addresses most of the
analysis questions with
considerable detail and
thought
Addresses all of the analysis
questions with a high degree
of detail and thoroughness
8A
8I
4I