AP chemistry
investigation #4
titration: how
much acid is in
various juices and
drinks
2015 NSTA Chicago
Jamie Murray
Product Specialist- Chemistry
jamie.murray@vwr.com
(585)321-9468
AP Chemistry lab format
• Ward’s Science AP Chemistry Labs adhere to the
2013 College Board revisions
• Every investigation encourages students to use the
seven science practices
– Use models
– Use mathematics
– Formulate questions
– Plan and execute data collection strategies.
– Analyze and evaluate data
– Explain results
– Generalize data across domains
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structured vs. guided inquiry
• Each lab has at least two parts
– Structured Inquiry
• Usually a demonstration
– Guided Inquiry
• Student determines procedure (with
teacher approval)
• Students document all data and
processes (notebook)
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student guided inquiry
part 1: plan
General format (each step recorded)
1. Define the question or testable hypothesis
2. Describe the background information.
Include previous experiments
3. Describe experiment design with controls,
variables, and observations
4. Describe possible results and how they
could be interpreted
5. List the materials and methods to be used
6. Note potential safety issues
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student guided inquiry
part 2: execute
7. Document detailed procedure in lab
notebook including calculations,
concentrations, weights, volumes etc.
8. Record results including drawings, photos,
data print-outs, etc.
9. Record analysis of results
10. Draw conclusions based on results
compared to predictions
11. Discuss limitations of experiment
12. Consider direction of further study
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today’s experiment:
titration (acid-base)
• Titration is a procedure in which one
substance (titrant) is carefully added to
another (analyte) until a complete reaction
has occurred.
• The equivalence point occurs when the
quantity of the added titrant is the exact
amount necessary for a stoichiometric
reaction with the analyte.
– Exact point when reaction is complete
– Ideal/theoretical result of titration
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today’s experiment:
titration (acid-base)
• The end point is the point in a titration at
which there is a sudden visible change
in a physical property (ex. color) that
signals the reaction is complete.
– Used as a measure of the
equivalence point
• An indicator is a compound having a
physical property (usually color) that
changes abruptly near the equivalence
point of a chemical reaction.
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structured inquiry: standardization
& indicators
• Standardization is the process whereby the
concentration of a reagent is determined
by the reaction with a known quantity of
another chemical substance.
• Examples of indicators used to show end
point of reaction through color change:
– Methyl red, Bromothymol blue, and
Phenolphthalein
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room for error
• Indicator error
– Use an indicator with a range that is suitable
for analyte’s pH. Color will change at wrong
pH.
– Use only 2-3 drops of indicator. Too much
will alter the final solution’s pH.
• Titration error
– The difference between the amount of titrant
added to analyte to get to equivalence point
vs the end point.
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standardization of NaOH
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standardization of NaOH
1. Start with 5.0mL in a small beaker of 0.10 M
HCl (hydrochloric acid). Record substance
tested and amt in data table.
2. Add a few drops of phenolphthalein indicator
into the beaker of HCl. Record indicator used
and initial color in data table.
3. Note initial volume of 0.10 M NaOH (sodium
hydroxide) in the buret. Record in the data
table.
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standardization of NaOH
4. Using the buret, add 0.10 M NaOH dropwise
into the beaker of HCl until the color
changes. Carefully swirl beaker occasionally
to aid the reaction.
5. Note color change & final buret volume.
Record both in data table.
6. Repeat process using 5.0 mL of 0.1 M
C2H4O2 (acetic acid), again using 0.1 M
NaOH as titrant, with each of the indicators
listed on table 1B. Record all data in table 1B.
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standardization of NaOH
If we start with 5.0 mL of 0.1 M HCl, how much
0.1 M NaOH is needed to reach the
equivalence point of the reaction?
NaOH + HCl  NaCl + H20 (1:1 Ratio)
M1V1 = M2V2
V1 = M2V2
M1
V1 (L NaOH) = (0.1 mol/L HCl) x (0.005 L HCl)
0.1 mol/L NaOH
V1 = 0.005 L NaOH = 5.0 mL NaOH needed to
reach equivalence point
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example answers
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Results and analysis
• Why did we use phenolphthalein for the
titration between NaOH and HCl?
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Results and analysis
• Why did we use phenolphthalein for the
titration between NaOH and HCl?
• HCl is a very strong acid. Phenolphthalein had
the highest indicator range that was close to
the pH of HCl.
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Results and analysis
• Why did we use phenolphthalein for the
titration between NaOH and HCl?
• HCl is a very strong acid. Phenolphthalein had
the highest indicator range that was close to
the HCl pH.
• What does the color change of the indicator
signify?
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Results and analysis
• Why did we use phenolphthalein for the
titration between NaOH and HCl?
• HCl is a very strong acid. Phenolphthalein had
the highest indicator range that was close to
the HCl pH.
• What does the color change of the indicator
signify?
• First faint color change indicates the
equivalence point. The stronger change
happens at the end point of the reaction.
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guided inquiry: finding acid
concentrations in beverages
• Decide which indicator is best for each titration.
• Determine how much NaOH is required to
reach the reaction endpoint for each titration.
• Find the acid concentration of 3 common
beverages
– several dilutions for each beverage.
– Titrations for orange juice using
0.25 M
NaOH
– Titrations for coffee and tea using 0.10 M
NaOH
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possible indicators
Indicator
pKa Range
(ph)
Acid
Color
Base
Color
Methyl Red
4.95
4.86.0
Magenta
Yellow
Bromothymol
Blue
7.10
6.07.6
Yellow
Blue
Phenolphthalein
9.4
8.210.0
Colorless
Pink
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acid concentration activity
worksheet
• Given:
– Beverage dilutions for
testing
– Conc of NaOH to use for
each beverage
• Record:
– Change in buret volume for
each titration
– Initial beverage color
– Final beverage color
– Indicator used
• Calculate acid conc of
each 20mL sample
results/discussion
• Which indicators worked best for each
beverage? Why?
• pH changed more rapidly as equivalence point
was approached even with smaller amount of
NaOH added. Why? How could you tell this
was happening?
• What kind of issues (possible errors) did you
run into?
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questions?
contact us:
• Jamie Murray
– Product Specialist- Chemistry
– 585.321.9468
– jamie.murray@vwr.com
• Ward’s Product Technical Support
– 866.260.0501
– sciencehelp@vwr.com
• Ward’s Science Customer Care Experts
– 800.962.2660
– wardscs@vwr.com
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