Transcript 9.2 pH and Titrations Obj S3, S4, and S5

9.2 pH and Titrations
Obj S3, S4, and S5
Chemistry
Essential Questions
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How do the H+ and OH- concentrations
compare for acidic, basic, and neutral
solutions?
What is pH and how is it used to identify if
something is an acid or base?
What is a neutralization reaction?
What are indicators?
What are titrations?
How are titrations used to find out
concentration or volume of an unknown?
Hydrogen Ions from Water
The
reaction in which water molecules
produce ions is called the self-ionization
of water.
In
neutral solutions H+ and OH- are equal
in concentration
Basic solutions have more OH- and acidic
solutions have more H+
Hydrogen Ions from Water
In
the self-ionization of water, a proton
(hydrogen ion) transfers from one water
molecule to another water molecule.
Ion Product Constant for Water
The
product of the concentrations of the
hydrogen ions and hydroxide ions in water is
called the ion-product constant for water
(Kw).
This
is why a pH of 7 is neutral and the pH scale
goes to 14
pH
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pH is defined as the negative log of the
hydrogen ion concentration.
pH = - log [H+]
Acids are substances with a pH < 7.
Bases are substances with a pH >7.
Pure water is neutral and has pH = 7.
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[H+]= 10-pH
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Identifying Acids and Bases
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A
A
A
A
A
A
solution
solution
solution
solution
solution
solution
where
where
where
where
where
where
[H+]
[H+]
[H+]
[H+]
[H+]
[H+]
=
=
=
=
=
=
1.0 x 10-3
1.0 x 10-7
6.99 x 10-9
1.0 x 10-13
5.0 x 10-5
7.5 x 10-8
Identifying Acids and Bases (cont)
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Find [H+] given the following pHs
4.3
7.8
13
2.13
Neutralization Reactions
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Neutralization reactions are where the
products are neutral so neither bases or
acids
The products are usually salt and water
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Salt: ionic compound formed from acid and
base
KOH (aq)+ HCl (aq)→ KCl (aq)+ H2O (l)
Base
Acid
Salt
Water
Acid Base Reactions
Neutralization reactions are used to
determine the concentration of an
unknown acid or base using an acidbase titration.
 Indicators are used to determine the
point when the acid and base have
neutralized each other.
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Acid-Base indicators
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An acid-base indicator is a substance that
changes colors when exposed to acids or
bases.
Example: Phenolphthalein turns pink in a
base and remains colorless in an acid.
Red Cabbage juice has several different
colors depending on the pH.
Acid-Base Titration
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Titration is a technique in which a
standard solution is added little by little to
determine the concentration of an
unknown substance.
The standard solution is a solution where
you know the concentration.
Acid-Base Titration (cont)
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The point at which the two solutions are
chemically equivalent and fully reacted is
called the Equivalence point.
The end point is when the indicator first
permanently changes color and should be
a similar point in the reaction to the
equivalence point.
Titration Curve
•
A pH meter can be
used for the
titration and the
results graphed .
The following
graphs are pH
titration curves.
Weak Base with Strong Acid
Methyl orange could be added as an indicator for
the titration of a weak base by a strong acid.
Calculations for Acid-Base
Titration
Molarity of
Known
x
Volume of
known
=
Unknown
Molarity
x
Unknown
volume
Example: In a titration, 17.6 mL of acetic acid is used to neutralize
27.4 mL of a solution that is 0.215 M potassium hydroxide. What is
the concentration of the acetic acid solution?
(17.6 mL acid) (x) = (27.4 mL base)( 0.215M)
X = (27.4ml)(0.215M)/(17.6ml) = .335 M acetic
acid
Titration Problems
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Find the mL of 5.5 M KOH when reacted with 32
mL of 4.23 M HF
Find the mL of 7.9 M HC2H3O2 when reacted with
611 mL of 9.0 M NH3
Find the concentration of H2CO3 when 43 mL of
1.2 M NH3 is added to 66 mL of H2CO3
Find the concentration of 97 mL SO4- when 54
mL of 2.44 M HF is added to it.
Essential Questions
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How do the H+ and OH- concentrations
compare for acidic, basic, and neutral
solutions?
What is pH and how is it used to identify if
something is an acid or base?
What is a neutralization reaction?
What are indicators?
What are titrations?
How are titrations used to find out
concentration or volume of an unknown?
9.2 Tracked Assignment
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worksheet