Transcript Section 15.3

Monday, May 5th: “A” Day
Tuesday, May 6th: “B” Day
Agenda
Homework questions/collect
Sec. 15.2 quiz
Section 15.3: “Neutralizations and Titrations”
Neutralization reaction, equivalence point,
titration, titrant, standard solution, transition
range, end point
Homework:
Sec. 15.3 review, pg. 556: #1-12
Concept Review: “Neutralizations and Titrations”
Homework Questions/Problems
Practice pg. 545: #1,2,4
Sec. 15.2 review, pg. 547: #1-12
Sec. 15.2 Quiz
You may use your notes, your periodic table,
your book and a calculator to complete the quiz
on your own…
Good luck!
Neutralization
Neutralization reaction: the reaction of
hydronium ions and hydroxide ions to form water
molecules and a salt.
When solutions of a strong acid and a strong
base, having exactly equal amounts of H3O+(aq)
and OH−(aq) ions, are mixed, almost all of the
hydronium and hydroxide ions react to form
water.
H3O+(aq) + OH−(aq)  2 H2O(l)
*This is the correct representation of a
neutralization reaction*
Neutralization
Suppose that hydrochloric acid, HCl, and
sodium hydroxide, NaOH, are mixed.
The result will be a solution of only water and
the spectator ions sodium and chlorine.
This is just a solution of sodium chloride.
HCl (aq) + NaOH (aq)  NaCl (aq) + H2O (l)
The above representation can be misleading
because the reactants are really only H3O+ (aq)
and OH− (aq) ions and the only product is H2O (l).
Titrations
If an acidic solution is added gradually to a basic
solution, at some point the neutralization
reaction ends because the hydroxide ions are all
used up.
Likewise, if a basic solution is added to an acid,
eventually all of the hydronium ions will be used
up.
The point at which a neutralization reaction is
complete is known as the equivalence point.
 Equivalence point: the point at which the two
solutions used in a titration are present in
chemically equivalent amounts.
Titrations
When a solution of a strong base is added to a
solution of a strong acid, the equivalence point
occurs when the amount of added hydroxide
ions equals the amount of hydronium ions
originally present.
Titration: the gradual addition of one solution
to another to reach an equivalence point.
The purpose of a titration is to determine the
concentration of an acid or a base.
Titration
In addition to the acid and base, the equipment
needed to carry out a titration usually includes two
burets, a titration flask, and a suitable indicator.
One buret is for the acid solution, the other is for
the basic (alkaline) solution.
Titrant: a solution of known concentration that is
used to titrate a solution of unknown
concentration.
Titration
To find the concentration of the solution
being titrated, you must already know the
concentration of the titrant.
Standard solution: a solution of known
concentration.
The concentration of a standard solution has
usually been determined by reacting the
solution with a precisely weighed mass of a
solid acid or base.
Titration
A distinctively shaped graph, called a titration
curve, results when pH is plotted against titrant
volume.
Because the curve is steep at the equivalence
point, it is easy to locate the exact volume that
corresponds to a pH of 7.00.
A titration is exact only if the equivalence point
can be accurately detected.
Equivalence Point
This graph of pH
versus the volume
of 1.000 M NaOH
added to an HCl
solution indicates
that the
equivalence point
(pH = 7) occurred
after 38.6 mL of
titrant was added.
Indicators
Transition range: the pH range through which an
indicator changes color.
End point: the point in a titration at which a
marked color change takes place.
If an appropriate indicator is chosen, the end
point and the equivalence point will be the same.
Selecting an Indicator
In titrations of a strong acid by a strong base, the
equivalence point occurs at pH 7.
When a weak acid is titrated by a strong base,
the equivalence point is at a pH greater than 7.
The titration of a weak base and a strong acid,
the equivalence point is at a pH less than 7.
How to Perform a Titration
How to Perform a Titration
Titration Calculations
At the equivalence point in a titration of a
strong acid by a strong base, the amount of
hydroxide ion added equals the initial amount of
hydronium ion.
C: concentration (in moles per liter; M)
V: volume (in liters) of the solution
Sample Problem D, pg. 555
Calculating Concentration from Titration Data
A student titrates 40.00 mL of an HCl solution of
unknown concentration with a 0.5500 M NaOH
solution. The volume of base solution needed to
reach the equivalence point is 24.64 mL. What is
the concentration of the HCl solution in
moles/liter?
Sample Problem D, continued…
NaOH is a strong base so:
NaOH (s)
Na+ (aq) + OH- (aq)
0.5500 M
0.5500 M
C(H3O+) = ?
V(H3O+) = 40.00 mL = .04000 L
C(OH-) = 0.5500 M
V(OH-) = 24.64 mL = .02464 L
(CH3O+) (.04000 L) =(0.5500 M) (.02464 L)
C(H3O+) = C(HCl) = 0.3388 mol/L
Additional Example
If 20.60 mL of 0.0100 M aqueous HCl is required
to titrate 30.00 mL of an aqueous solution of NaOH
to the equivalence point, what is the molarity of
the NaOH solution?
Additional Example, continued…
HCl is a strong acid so:
HCl (aq) + H2O (l)
H3O+ (aq) + Cl- (aq)
0.0100 M
0.0100 M
C(H3O+) = 0.0100 M
V(H3O+) = 20.60 mL = .02060 L
C(OH-) = ?
V(OH-) = 30.00 mL = .03000 L
(0.0100 M) (.02060 L) = (COH-) (0.03000 L)
C(OH-) = C(NaOH) = 0.00687 M
This one’s a little harder…
If 72.10 mL of 0.543 M H2SO4 completely titrates
39.00 mL of KOH solution, what is the molarity of the
KOH solution?
(Hint: H2SO4 has 2 ionizable protons…)
H2SO4 is a strong acid so:
H2SO4 (aq) + 2 H2O (l)
SO42- (aq) + 2 H3O+ (aq)
0.543 M
1.086 M
Because of the 1:2 ratio, 1 mole of H2SO4 produces 2
moles of H3O+:
2 [H2SO4] = [H3O+]
2 (0.543 M) = 1.086 M
Additional Practice, continued…
C(H3O+) = 1.086 M
V(H3O+) = 72.10 mL = .07210 L
C(OH-) = ?
V(OH-) = 39.00 mL = .03900 L
(1.086 M) (.07210 L) = (COH-) (.03900 L)
C(OH-) = C(KOH) = 2.008 M
Homework
Section 15.3 review, pg. 556: #1-12
Concept Review: “Neutralizations and Titrations”
Looking Ahead:
Wednesday/Thursday:
Virtual Titration
Lab Write-up
Titration worksheet
Friday/Monday:
Titration Lab