Aqueous Reactions © 2015 Pearson Education, Inc. Compilation Presentation Chapter 4 [4.5] Reactions in Aqueous Solution James F. Kirby Quinnipiac University Hamden, CT [Edited by E.Schneider, Sept 2015]

Aqueous Reactions © 2015 Pearson Education, Inc. Oxidation-Reduction Reactions Loss of electrons is oxidation. Gain of electrons is reduction. One cannot occur without the other. The reactions are often called redox reactions.

Aqueous Reactions © 2015 Pearson Education, Inc. Displacement Reactions Cu(s) + 2 Ag + (aq)  Cu 2+ (aq) + 2 Ag(s) In displacement reactions, ions oxidize an element. In this reaction, silver ions oxidize copper metal: The reverse reaction does NOT occur. Why not?

Aqueous Reactions © 2015 Pearson Education, Inc. Activity Series Elements higher on the activity series are more reactive. They are more likely to exist as ions.

Aqueous Reactions © 2015 Pearson Education, Inc. Metal/Acid Displacement Reactions The elements above hydrogen will react with acids to produce hydrogen gas. The metal is oxidized to a cation.

Aqueous Reactions © 2015 Pearson Education, Inc. a.Yes b.No Does a reaction occur when an aqueous solution of NiCl 2 (aq) is added to a test tube containing strips of metallic zinc?

Aqueous Reactions © 2015 Pearson Education, Inc. a.Yes b.No Does a reaction occur when an aqueous solution of NiCl 2 (aq) is added to a test tube containing strips of metallic zinc?

Aqueous Reactions © 2015 Pearson Education, Inc. a.Yes b.No Does a reaction occur when NiCl 2 (aq) is added to a test tube containing Zn(NO 3 ) 2 (aq)?

Aqueous Reactions © 2015 Pearson Education, Inc. a.Yes b.No Does a reaction occur when NiCl 2 (aq) is added to a test tube containing Zn(NO 3 ) 2 (aq)?

Aqueous Reactions © 2015 Pearson Education, Inc.

Aqueous Reactions © 2015 Pearson Education, Inc. Why does the solution in the figure below turn blue? a. Cu 2+ (aq) ions are blue. b.NO 3 – (aq) ions are blue. c.Ag(s) is blue. d.H 2 O is blue.

Aqueous Reactions © 2015 Pearson Education, Inc. Why does the solution in the figure below turn blue? a. Cu 2+ (aq) ions are blue. b.NO 3 – (aq) ions are blue. c.Ag(s) is blue. d.H 2 O is blue.

Aqueous Reactions © 2015 Pearson Education, Inc. Solution Solve Because Mg is above Fe in the table, the reaction occurs. The magnesium salt formed in the reaction is MgCl 2, meaning the balanced molecular equation is Both FeCl 2 and MgCl 2 are soluble strong electrolytes and can be written in ionic form, which shows us that Cl – is a spectator ion in the reaction. The net ionic equation is The net ionic equation shows that Mg is oxidized and Fe 2+ is reduced in this reaction. Sample Exercise 4.10 Will an aqueous solution of iron(II) chloride oxidize magnesium metal? If so, which element is oxidized and which is reduced?

Aqueous Reactions © 2015 Pearson Education, Inc. Practice Exercise 1 Which of these metals is the easiest to oxidize? (a) gold, (b) lithium, (c) iron, (d) sodium, (e) aluminum. Practice Exercise 2 Which of the following metals will be oxidized by Pb(NO 3 ) 2 : Zn, Cu, Fe? Sample Exercise 4.10 Determining When an Oxidation- Reduction Reaction Can Occur Continued

Aqueous Reactions © 2015 Pearson Education, Inc. Sample Integrative Exercise Putting Concepts Together A sample of 70.5 mg of potassium phosphate is added to 15.0 mL of M silver nitrate, resulting in the formation of a precipitate. (a) Write the molecular equation for the reaction. (b) What is the limiting reactant in the reaction? (c) Calculate the theoretical yield, in grams, of the precipitate that forms.

Aqueous Reactions © 2015 Pearson Education, Inc. Solution (a ) Potassium phospPotassium phosphate chemical formula is K 3 PO 4. Silver nitrate chemical formula is AgNO 3. The solution contains, K +, PO 4 3–, Ag +, and NO 3 – ions before the reaction occurs. According to the solubility guidelines in Table 4.1, Ag + and PO 4 3– form an insoluble compound, so Ag 3 PO 4 will precipitate from the solution. K + and NO 3 – will remain in solution because KNO 3 is water soluble. Thus, the balanced molecular equation for the reaction is K 3 PO 4 (aq) + 3 AgNO 3 (aq) → Ag 3 PO 4 (s) + 3 KNO 3 (aq) Sample Integrative Exercise Putting Concepts Together A sample of 70.5 mg of potassium phosphate is added to 15.0 mL of M silver nitrate, resulting in the formation of a precipitate. (a) Write the molecular equation for the reaction. (b) What is the limiting reactant in the reaction? (c) Calculate the theoretical yield, in grams, of the precipitate that forms.

Aqueous Reactions © 2015 Pearson Education, Inc. (b ) Limiting Reagent: Moles of K 3 PO 4 is calculated from the mass of the sample using the molar mass as a conversion factor We determine the number of moles of AgNO 3 from the volume and molarity of the solution. (Section 4.5) Converting milliliters to liters and then to moles, we have Comparing the amounts of the two reactants, we find that there are (7.5 × 10 –4 ) / × (0 –4 ) = 2.3 times as many moles of AgNO 3 as there are moles of K 3 PO 4. According to the balanced equation, however, 1 mol K 3 PO 4 requires 3 mol AgNO 3. Thus, there is insufficient AgNO 3 to consume the K 3 PO 4, and AgNO 3 is the limiting reactant. Sample Integrative Exercise Putting Concepts Together Continued

Aqueous Reactions © 2015 Pearson Education, Inc. (c) The precipitate is Ag 3 PO 4, whose molar mass is 3(107.9) (16.0) = g / mol. To calculate the number of grams of Ag 3 PO 4 that could be produced in this reaction (the theoretical yield), we use the number of moles of the limiting reactant, converting mol AgNO 3 → mol Ag 3 PO 4 → g Ag 3 PO 4. We use the coefficients in the balanced equation to convert moles of AgNO 3 to moles Ag 3 PO 4, and we use the molar mass of Ag 3 PO 4 to convert the number of moles of this substance to grams. The answer has only two significant figures because the quantity of AgNO 3 is given to only two significant figures. Sample Integrative Exercise Putting Concepts Together Continued