Neutralization and Titration

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Acid + Base  Salt + Water
 Salt = ionic compound made up of the anion
from an acid and the cation from a base.
 REMEMBER: when any strong acid reacts with
any strong base in the mole ratio from a
balanced chemical equation, a neutral
aqueous solution of a salt is formed.
 Note: reactions between acids and bases of
different strengths usually don’t result in
neutral solutions.
 1.
pH probe
 2. Indicator

An indicator is usually a weak monoprotic acid
with a complex organic structure.
HIn(aq) ↔ H+(aq) + In-(aq)
Phenolphthalein:
Color 1
Color 2
(You do not
need to know
this structure)
 What
are they? How do they work?
 Antacids are supposed to decrease the
amount of hydrochloric acid in the stomach
by reacting with excess acid (ie. they
neutralize your stomach acid). They are used
in the treatment of gastric hyperacidity and
peptic ulcers. Some of the ingredients in
antacids are: Magnesia (MgO), milk of
magnesia (Mg(OH)2, calcium carbonate
(CaCO3), sodium bicarbonate (NaHCO3),
dihydroxyaluminum sodium carbonate
(NaAl(OH)2CO3), aluminum hydroxide gel
(Al(OH)3).
 What’s
going to happen when I put the TUMS
(main ingredient is CaCO3) in the acid?

What if I add phenolphthalein?
 What
if I add bromythol blue?
 What
if I add bromocresol green?
 What
volume of 0.250 M H2SO4(aq) is needed to
react completely with 37.2 mL of 0.650 M
KOH(aq)?

Step 1: Balanced equation
H2SO4(aq) + 2KOH(aq)  K2SO4(aq) +2H2O(l)

Step 2: amount (mols) of KOH=
0.650 mol/L x 0.0372 L = 0.02418 mol KOH
Step 3: mols H2SO4 (reacts with KOH in 1:2 ratio)=
0.02418 mol KOH x (
) = 0.01209 mol H2SO4


Step 4: Volume H2SO4(aq)
=
= 0.04836 L
Therefore, the volume of H2SO4(aq) required is 48.4 mL.
NOW: If you are more comfortable working with this
equation, go ahead! Just be careful with your mole
ratios!
2CAVA = CBVB
H2SO4(aq)
 What
volume of 0.150 M hydrochloric acid is
needed to neutralize 80.0 mL of 0.0045 M
calcium hydroxide?
Moving On…
 It’s
a method chemists use to determine the
concentration of a solution by observing it’s
quantitative reaction with a solution of
known concentration

In other words, if we have some volume of acid
and we want to determine it’s concentration, we
can “titrate” it with a solution of base of which
we know the concentration (or vice versa)
Titrant: what we
put in the buret
Endpoint = point at which your
indicator (just) changes color
 Graph
of the pH of an acid (or base) vs the
volume of titrant base (or acid)
 You need to know what these types of
titration curves look like:



Strong acid + strong base
Weak acid + strong Base
Weak base + strong acid
 You
do not need to know the curve for the
titration of a weak acid with weak base

Why? It’s complicated!
Strong acid +
strong base
titrations:
equivalence point
is always pH 7
 Want an indicator
that has an
endpoint close to
the equivalence
point

 Equivalence
point is greater
than pH 7
 Equivalence
point is less
than pH 7
 http://www.mhhe.com/physsci/chemistry/a
nimations/chang_7e_esp/crm3s5_5.swf
 http://wwwchem.uwimona.edu.jm:1104/sof
tware/titr.html
Assignment for the remainder of class:
 In groups of 2-3, go online and find one of the
following:

An article relating in acids and/or bases
An application (industrial, medicinal, environmental,etc.)
of acids/bases
 A cool experiment relating to acids or bases



Prepare to give us the “gist” of what you discover in
2-3 minutes 

Need help? You could look at:






Natural buffer systems
Acid-base chemistry and baking
Acid rain
Use of indicators (ex. medicine)
Natural acid-base remedies (ex. bee/wasp stings)
Acidic or basic drugs extracted from natural sources

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