Solution Stoichiometry
•
Solution Stoichiometry uses molarity as a
conversion factor between volume and moles of a
substance in a solution.
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Titrations
Titration: A technique for determining the concentration of
a solution by measuring the volume of one solution needed
to completely react with another solution.
This is a special case of a Limiting Reagent!
Usually the reaction of an acid with a base.
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Titrations
Analyte: the solution of unknown concentration but known
volume.
Titrant: the solution of known concentration.
Analyte + Titrant → Products
Process: Add titrant until all of the analyte has reacted, then
record the volume of titrant added.
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Titrations
Equivalence Point: the point at which exactly the right
volume of titrant has been added to complete the reaction.
Indicator: substance that changes color when an excess of
titrant has been added (phenolphthalein, bromocresol
green).
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Phenolphthalein
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Methyl Orange
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Delivery of Titrant
Adding titrant drop-wise.
• How many drops fit into 1mL?
•
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Process: Calibration-hold the pipette
in the VERTICAL position and
deliver the titrant into a graduated
cylinder while counting every drop.
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Copy the following “Data Tables”
Vinegar
Measurement
Antacid
Value
Measurement
Vinegar
Analyte
Volume
Titrant
NaOH
Molarity
1.00M
Calibration
Antacid
Analyte
10mL
Quantity 1tablet in 20mL H2O
Titrant
HCl
Molarity
3.00M
Calibration
Volume ____drops ____mL
Volume ____drops ____mL
Indicator
Value
phenolphthalein
Methyl orange
Indicator
Acid
Colorless
Acid
Pink
Base
Pink
Base
Yellow
Reaction
Mole Ratio
Reaction
Mole Ratio
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Titrations Calculations
1.
2.
3.
Find the number of moles
of titrant added to reach
the endpoint.
Determine the moles of
analyte that must have
been present (use
stoichiometric coefficients).
Determine the
concentration of analyte
that must have been
present in the flask (use
the volume of analyte).
•
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Titrations
Example #1: 14.84 mL of an HCl solution of unknown
concentration is titrated with standard NaOH solution. At
the equivalence point, 25.0 mL of the 0.675 M NaOH has
been added. Calculate the concentration of the HCl
solution.
NaOH + HCl → NaCl + H2O
Hints: Titrant = ?moles Analyte = ?moles ?Liters
Answer = 1.14 M
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Stoichiometry
Measurement
Calculation
moles of titrant
moles of analyte (use
stoichiometric coefficients).
concentration of analyte
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