Monday, May 5 th : “A” Day Tuesday, May 6 th : “B” Day Agenda  Homework questions/collect  Sec quiz  Section 15.3: “Neutralizations and Titrations” Neutralization reaction, equivalence point, titration, titrant, standard solution, transition range, end point  Homework: Sec review, pg. 556: #1-12 Concept Review: “Neutralizations and Titrations”

Homework Questions/Problems  Practice pg. 545: #1,2,4  Sec review, pg. 547: #1-12

Sec 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 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) *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) + H 2 O (l)  The above representation can be misleading because the reactants are really only H 3 O + (aq) and OH − (aq) ions and the only product is H 2 O (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  A titration is exact only if the equivalence point can be accurately detected.

Equivalence Point  This graph of pH versus the volume of 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

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 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?

Sample Problem D, continued… NaOH is a strong base so: NaOH (s) Na + (aq) + OH - (aq) M M C (H3O+) = ? V (H3O+) = mL = L C (OH-) = M V (OH-) = mL = L (C H3O+ ) ( L) =( M) ( L) C (H3O+) = C (HCl) = mol/L

Additional Example  If mL of M aqueous HCl is required to titrate 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) + H 2 O (l) H 3 O + (aq) + Cl - (aq) M M C (H3O+) = M V (H3O+) = mL = L C (OH-) = ? V (OH-) = mL = L ( M) ( L) = (C OH- ) ( L) C (OH-) = C (NaOH) = M

This one’s a little harder…  If mL of M H 2 SO 4 completely titrates mL of KOH solution, what is the molarity of the KOH solution? (Hint: H 2 SO 4 has 2 ionizable protons…) H 2 SO 4 is a strong acid so: H 2 SO 4 (aq) + 2 H 2 O (l) SO 4 2- (aq) + 2 H 3 O + (aq) M M Because of the 1:2 ratio, 1 mole of H 2 SO 4 produces 2 moles of H 3 O + : 2 [H 2 SO 4 ] = [H 3 O + ] 2 (0.543 M) = M

Additional Practice, continued… C (H3O+) = M V (H3O+) = mL = L C (OH-) = ? V (OH-) = mL = L (1.086 M) ( L) = (C OH- ) ( L) C (OH-) = C (KOH) = 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