Neutralization & Titrations Packet #27

Lunch Time After a few hours of challenging classes, most students are anxious to depart for their lunch.

The Aftermath… However, there are times when a meal, provided in any location such a restaurant, school or even at home, can result in one developing an upset stomach. What does the individual do for aid?

The Aftermath II Some individuals may turn to Pepto Bismol Used to neutralize the acid in the stomach. Contains: - Sodium hydrogen carbonate Aluminum hydroxide Magnesium hydroxide

Mixing of Acids & Bases If a strong acid, and a strong base, are mixed together, a neutral solution (pH = 7) occurs. The final solution has properties that are characteristic of neither an acid or a base. HCl(aq) + NaOH(aq)  NaCl(aq) + H2O

Neutralization Reactions I When solutions of a strong acid and a strong base, having equal amounts of H3O+(aq) or H+ and OH-(aq) ions are mixed, almost all of the hydronium ions and hydroxide ions react to form water H3O+(aq) + OH-(aq)  2H2O(l)

Neutralization Reactions II When hydrochloric acid and sodium hydroxide are mixed together, an aqueous solution of sodium chloride is produced—salt in water. In general, most neutralization reaction will produce water and a salt (ionic compound). HCl (aq) + NaOH (aq)  NaCl (aq) + H2O

Titrations

Titrations I If an acidic solution is added gradually to a basic solution, at some point the neutralization reaction ends because the hydroxide ions (OH-) become used up. Likewise, if a basic solution is gradually added to an acidic solution, eventually all of the hydronium ions (H3O+) become used up. The point at which a neutralization reaction is complete is called the equivalence point.

Titrations II The gradual addition of one solution to another to reach an equivalence point is called a titration. The purpose of a titration is to determine the concentration of an acid or a base. If an acid is to be titrated with a base, one buret is used to measure the volume of the acid solution titrated into the titration flask.

Titrations III—A Look Ahead to the Titration Lab If an acid is to be titrated with a base, one buret is used to measure the volume of the acid solution dispensed into the titration flask. A second buret is used to deliver and measure the volume of the alkaline solution (basic solution), aka titrant, added to the acidic solution (aka analyte). This may also be done in the opposite direction where the acid (titrant) added to the base (analyte).

Titrations IV—Titration Curve As a titrant is added to the flask containing the solution of unknown concentration (analyte), pH is measured. A distinctively shaped graph, called a titration curve, results when pH is plotted against titrant volume. A titration is exact only if the equivalence point can be accurately detected. A pH meter, or pH indicators, can be used to monitor the pH during the titration.

Problem Set I Determine the volume of 0.100 M NaOH needed to titrate 50.0 mL of 0.200 M HNO3. Special notes: - HNO3 contains H+ and NO3- ions. NaOH contains Na+ and OH- ions. The neutralization reaction should be: - H+ (aq) + OH- (aq)  H2O (l)

Problem Set I Determine the volume of 0.100 M NaOH needed to titrate 50.0 mL of 0.200 M HNO3. Step #1 Determine the moles of H+ originally present in the 50.0 mL sample of 0.200 M HNO3 The problem has the characteristics of a limiting reagent problem. Use the molarity equation. 1.00 * 10-2 mol H+

Problem Set I Determine the volume of 0.100 M NaOH needed to titrate 50.0 mL of 0.200 M HNO3. Step #2 What volume of NaOH will provide the scientist with 1.00 * 10-2 mol OH-? Again, use the molarity equation This now becomes the answer to the problem. 0.001 L = 100 mL.

Problem Set II Calculate the volume of 0.3000 M HCl needed to titrate 75.00 mL of 0.1500 M KOH(aq). Follow the same steps completed in problem set #1.

Review