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AgendaHomework questions/collectSec. 15.2 quizSection 15.3: “Neutralizations and Titrations”

Neutralization reaction, equivalence point, titration, titrant, standard solution, transition range, end point

Homework:Sec. 15.3 review, pg. 556: #1-12Concept Review: “Neutralizations and Titrations”

Homework Questions/ProblemsPractice pg. 545: #1,2,4Sec. 15.2 review, pg. 547: #1-12

Sec. 15.2 QuizYou may use your notes, your periodic table,

your book and a calculator to complete the quiz on your own…

Good luck!

NeutralizationNeutralization 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*

NeutralizationSuppose 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).

TitrationsIf 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.

TitrationsWhen 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.

TitrationTo 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.

TitrationA 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.

IndicatorsTransition 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 IndicatorIn 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 CalculationsAt 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. 555Calculating 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 LC(OH-) = 0.5500 MV(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 MV(H3O+) = 20.60 mL = .02060 LC(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 MBecause 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

HomeworkSection 15.3 review, pg. 556: #1-12Concept Review: “Neutralizations and Titrations”

Looking Ahead:Wednesday/Thursday:

Virtual TitrationLab Write-up

Titration worksheetFriday/Monday:

Titration Lab