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Friday, May 6 th : “A” Day AgendaPowerPoint Presentation

Friday, May 6 th : “A” Day Agenda

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Friday, May 6th: “A” DayAgenda

- Homework questions/problems/collect
- Quiz over section 15.2: “Acidity, Basicity, and pH”
- 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: #1-10
- Concept Review: “Neutralizations and Titrations”
- Lab Write-Up: “Titration of an Acid and a Base”

Section 15.2 Quiz “Acidity, Basicity, and pH”

- You may use your guided notes, your book, and a partner to complete the quiz.

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)

*correct*

Neutralization

- Supposethat 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 + NaOH NaCl + H2O

- This is just a solution of sodium chloride.
- This representation can be misleading because the only reactants are H3O+(aq) and OH−(aq) ions and the only product is H2O.

Titrations

- If an acidic solution is added gradually to a basic solution, at some point the neutralization reaction ends because the hydroxide ions are 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 two solutions, 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 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.

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)
- V: volume (in liters) of the solution

Titration Calculations

- An easier way to think of this:
(C Acid)(V Acid) = (C Base) (V Base)

- C: concentration (in moles per liter)
- 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?

(CAcid) (VAcid) = (CBase) (VBase)

Sample Problem D, continued…

- NaOH is a strong base so:
NaOH Na + + OH-

0.5500 M 0.5500 M

- C(acid) = ?
- V(acid) = 40.00 mL = .04L
- C(base) = 0.5500 M
- V(base) = 24.64 mL = .02464 L
(CAcid) (VAcid) = (CBase) (VBase)

- C (Acid) (.04 L) =(0.5500 M) (.02464 L)
C(acid) = 0.3388 mol/L

Additional Practice

If 72.1 mL of 0.543 M H2SO4 completely titrates 39.0 mL of KOH solution, what is the molarity of the KOH solution?

- H2SO4 is a strong acid so:
H2SO4 + 2 H2O SO42- + 2 H3O +

0.543 M 1.086 M

- Because of the 1:2 ratio, 1 mole of H2SO4 makes 2 moles of H3O +.
- [H3O+] = 2 [H2SO4] = 2 (0.543 M) = 1.086 M

Additional Practice, continued…

(CAcid) (VAcid) = (CBase) (VBase)

C(acid) = 1.086 M

V(acid) = 72.1 mL = .0721 L

C(base) = ?

V(base) = 39.0 mL = .0390 L

(1.086 M) (.0721 L) = (C Base) (.0390L)

C(base) = 2.01 M

Homework

- Section 15.3 review, pg. 556: #1-10
- Concept Review: “Neutralizations and Titrations”
- Lab Write-Up: “Titration of an Acid and a Base”
Looking Ahead:

U of I 3D-Printing Presentation on Tuesday!

Titration lab on Thursday

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