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Solution StoichiometrySolution Stoichiometry

• Solution Stoichiometry uses molarity as a conversion factor between volume and moles of a substance in a solution.

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TitrationsTitrations

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.

TitrationsTitrations

Analyte: the solution of unknown concentration but known

volume.

Titrant: the solution of known concentration.

Process: Add titrant until all of the analyte has reacted, then

record the volume of titrant added.

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Analyte + Titrant → Products

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TitrationsTitrations

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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PhenolphthaleinPhenolphthalein

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Methyl OrangeMethyl Orange

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Delivery of TitrantDelivery of Titrant

• Adding titrant drop-wise.• How many drops fit into 1mL?

• 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”Copy the following “Data Tables”

VinegarMeasurement Value

Analyte

Volume

Titrant

Molarity

Calibration

Volume

Indicator

Acid

Base

Reaction

Mole Ratio

AntacidMeasurement Value

Analyte

Quantity

Titrant

Molarity

Calibration

Volume

Indicator

Acid

Base

Reaction

Mole Ratio9

1.00M

10mL

NaOH

phenolphthalein

Colorless

Vinegar

Pink

3.00M

Methyl orange

Pink

Yellow

1tablet in 20mL H2O

HCl

Antacid

____drops ____mL ____drops ____mL

Titrations CalculationsTitrations Calculations

1. Find the number of moles of titrant added to reach the endpoint.

2. Determine the moles of analyte that must have been present (use stoichiometric coefficients).

3. Determine the concentration of analyte that must have been present in the flask (use the volume of analyte).

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TitrationsTitrations

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

StoichiometryStoichiometry

Measurement Calculation

moles of titrant

moles of analyte (use stoichiometric coefficients).

concentration of analyte

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