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Friday, May 6 th : “A” Day Agenda  Homework questions/problems/collect  Quiz over section 15.2: “Acidity, Basicity, and pH”  Section 15.3: “Neutralizations.

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Presentation on theme: "Friday, May 6 th : “A” Day Agenda  Homework questions/problems/collect  Quiz over section 15.2: “Acidity, Basicity, and pH”  Section 15.3: “Neutralizations."— Presentation transcript:

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2 Friday, May 6 th : “A” Day Agenda  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 review, pg. 556: #1-10 Concept Review: “Neutralizations and Titrations” Lab Write-Up: “Titration of an Acid and a Base”

3 Section 15.2 Quiz “Acidity, Basicity, and pH”  You may use your guided notes, your book, and a partner to complete the quiz.

4 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 H 3 O + (aq) and OH − (aq) ions, are mixed, almost all of the hydronium and hydroxide ions react to form water. H 3 O + (aq) + OH − (aq)  2 H 2 O(l) *correct*

5 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 + NaOH  NaCl + H 2 O  This representation can be misleading because the only reactants are H 3 O + (aq) and OH − (aq) ions and the only product is H 2 O.

6 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.

7 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.

8 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.

9 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.

10 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  A titration is exact only if the equivalence point can be accurately detected.

11 Equivalence Point  This graph of pH versus the volume of M NaOH added to an HCl solution indicates that the equivalence point occurred after 38.6 mL of titrant was added.

12 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.

13 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.

14 How to Perform a Titration

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16 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

17 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

18 Sample Problem D, pg. 555 Calculating Concentration from Titration Data A student titrates mL of an HCl solution of unknown concentration with a M NaOH solution. The volume of base solution needed to reach the equivalence point is mL. What is the concentration of the HCl solution in moles/liter? (C Acid ) (V Acid ) = (C Base ) (V Base )

19 Sample Problem D, continued…  NaOH is a strong base so: NaOH Na + + OH M M  C (acid) = ?  V (acid) = mL =.04L  C (base) = M  V (base) = mL = L (C Acid ) (V Acid ) = (C Base ) (V Base )  C (Acid) (.04 L) =( M) ( L) C (acid) = mol/L

20 Additional Practice If 72.1 mL of M H 2 SO 4 completely titrates 39.0 mL of KOH solution, what is the molarity of the KOH solution?  H 2 SO 4 is a strong acid so: H 2 SO H 2 O SO H 3 O M M  Because of the 1:2 ratio, 1 mole of H 2 SO 4 makes 2 moles of H 3 O +.  [H 3 O + ] = 2 [H 2 SO 4 ] = 2 (0.543 M) = M

21 Additional Practice, continued… (C Acid ) (V Acid ) = (C Base ) (V Base ) C (acid) = 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

22 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 No Flip-Flops!


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