TITRATIONS
Neutralization
• Reaction between an acid and a base that produces water and a salt
• (Type of reaction: Double displacement)
Example:
• H2SO4 (aq) + 2 KOH (aq)  K2SO4 (aq) + 2 HOH (l)
• Acid
Base
Salt
Water
• Remember: HOH = H2O
Acid/base Indicators
• An indicator is a substance that changes color
when the pH changes.
• Common indicators:
• Litmus – changes from red to blue
• pH Range: 5.0-8.0
• Phenolphthalein – changes from clear (acidic) to
pink (basic)
• pH Range: 8.2-10.0
• Bromothymol blue – yellow (acidic) to blue (basic)
• pH range: 6.0-7.6
Video of the day: Cabbage pH
Universal indicator
Indicators
Titration
• Titration is controlled addition of a solution with a
known concentration to a solution of unknown
concentration.
• Titrations enable us to find an unknown concentration by finding two
things that are stoichiometrically equivalent
Using a buret to do titrations
Base or acid is slowly
added until the
solution changes
color. The color
change tells you that
all of the base or acid
has reacted so you
can stop adding
more.
Equivalence point
• Equivalence point: The point in a titration where the acid and base
are stoichiometrically equivalent
• There is no excess base or excess acid. All of the base and acid has reacted.
• End point: The point in a titration when the color of the solution
changes permanently.
Titration curve
An indicator is used to find
the endpoint . You choose
and indicator so that the
endpoint is in the rapid rise
region of the curve.
Therefore the endpoint =
equivalence point
Finding an unknown
Molarity or volume
• Use (#H+) MaVa=MbVb (#OH-)
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H+ = Number of hydrogen ions (H+) from acid (see next slide for an example)
Ma = molarity (M) of acid
Va = volume of acid used in titration
Mb = molarity (M) of base
Vb = volume of base used in titration
(#OH-) = Number of hydroxide (OH-) ions from base (see next slide for an example)
Finding an unknown
Molarity or volume
• Use (#H+) MaVa=MbVb (#OH-)
• Remember at equivalence point, moles of acid = moles of base
• You must remember to use a mole ratio when the acid and base
don’t react in a 1:1 mol ratio
• Example: H3PO4 reacts with Ba(OH)2
• Mol H+ = 3
• Mol OH- = 2
• (3) MaVa=MbVb (2)
Example – Per. 3
• When 10.0 mL of a 0.125 M solution of
hydrochloric acid, HCl, is titrated with a 0.100 M
solution of potassium hydroxide, KOH, what is the
volume of base needed to neutralize the acid?
• HCl + KOH  KCl + HOH
• (#H+) MaVa= MbVb (#OH-)
• (1)(0.125 M)(10.0 mL) = (0.100 M) Vb (1)
• Mb = 0.125 M x 10.0 mL = 12.5 mL KOH
0.100 M
Example – Per. 4
• When 10.0 mL of a 0.125 M solution of
hydrochloric acid, HCl, is titrated with12.5 mL of
potassium hydroxide, KOH, what is the
concentration of base needed to neutralize the
acid?
• HCl + KOH  KCl + HOH
• (#H+) MaVa= MbVb (#OH-)
• (1)(0.125 M)(10.0 mL) = Mb (12.5 mL) (1)
• Mb = 0.125 M x 10.0 mL = 0.1 M KOH
12.5 mL