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Chapter 4 Reactions in Aqueous Solution Lecture Presentation © 2012 Pearson Education, Inc. Ashley Warren Kings High School AP Chemistry Lecture Presentation.

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Presentation on theme: "Chapter 4 Reactions in Aqueous Solution Lecture Presentation © 2012 Pearson Education, Inc. Ashley Warren Kings High School AP Chemistry Lecture Presentation."— Presentation transcript:

1 Chapter 4 Reactions in Aqueous Solution Lecture Presentation © 2012 Pearson Education, Inc. Ashley Warren Kings High School AP Chemistry Lecture Presentation © 2012 Pearson Education, Inc.

2 Aqueous Reactions © 2012 Pearson Education, Inc. Solutions An aqueous solution is a solution in which water is the dissolving medium. Solutions are defined as homogeneous mixtures of two or more pure substances. The solvent is present in greatest abundance. All other substances are solutes.

3 Aqueous Reactions © 2012 Pearson Education, Inc. Dissociation An electrolyte is a substances that dissociates into ions when dissolved in water. A nonelectrolyte may dissolve in water, but it does not dissociate into ions when it does so.

4 Aqueous Reactions © 2012 Pearson Education, Inc. Electrolytes A strong electrolyte dissociates completely when dissolved in water. A weak electrolyte only dissociates partially when dissolved in water.

5 Aqueous Reactions Chemical Equilbrium HCl (aq) H + (aq) + Cl - (aq) CH 3 COOH (aq) = CH 3 COO - (aq) + H + (aq) What is the biggest difference between the two reactions above? Which represents a strong electrolyte and which represents a weak? Why? © 2012 Pearson Education, Inc.

6 Aqueous Reactions © 2012 Pearson Education, Inc. Dissociation When an ionic substance dissolves in water, the solvent pulls the individual ions from the crystal and solvates them. This process is called dissociation.

7 Aqueous Reactions Solvation Solvation helps stabilize the ions in the solution and prevents cations and anions from recombining. –Why does water help do this? Since ions are free to move, they become dispersed uniformly. © 2012 Pearson Education, Inc.

8 Aqueous Reactions © 2012 Pearson Education, Inc. Electrolytes and Nonelectrolytes Soluble ionic compounds tend to be electrolytes. Why? Molecular compounds tend to be nonelectrolytes, except for acids and bases.

9 Aqueous Reactions © 2012 Pearson Education, Inc. Strong Electrolytes Are… Strong acids Strong bases

10 Aqueous Reactions © 2012 Pearson Education, Inc. Precipitation Reactions Reactions that result in the formation of an insoluble product are called precipitation reactions Precipitates are insoluble solids formed by a reaction in solution. We know if ppts. form bc we can predict them by the solubility guidelines. Pb(NO 3 ) 2 (aq) + 2 KI (aq) PbI 2 (s) + 2KNO 3 (aq)

11 Aqueous Reactions Solubility The solubility of a substance at a given temperature is the amount of the substance that can be dissolved in a given quantity of solvent at the given temperature. Any substance with a solubility less than 0.01 mol/L will be referred to as insoluble.

12 Aqueous Reactions © 2012 Pearson Education, Inc. Metathesis (Exchange) Reactions Metathesis comes from a Greek word that means to transpose. It appears as though the ions in the reactant compounds exchange, or transpose, ions. Reactions in which cations and anions appear to exchange partners conform to the general equation: –AX + BY AY + BX AgNO 3 (aq) + KCl(aq)

13 Aqueous Reactions Metathesis Reactions Steps to complete and balance these reactions: –Use the chemical formulas to determine which ions are present. –Write the chemical formulas of the products by combining the cation from one reactant with the anion of the other, using ionic charges to determine the correct subscripts. –Check the solubilities of the products. –Balance. © 2012 Pearson Education, Inc.

14 Aqueous Reactions © 2012 Pearson Education, Inc. Solution Chemistry It is helpful to pay attention to exactly what species are present in a reaction mixture (i.e., solid, liquid, gas, aqueous solution). If we are to understand reactivity, we must be aware of just what is changing during the course of a reaction.

15 Aqueous Reactions © 2012 Pearson Education, Inc. Molecular Equation The molecular equation lists the reactants and products in their molecular form: AgNO 3 (aq) + KCl(aq) AgCl(s) + KNO 3 (aq)

16 Aqueous Reactions © 2012 Pearson Education, Inc. Complete Ionic Equation In the complete ionic equation all strong electrolytes (strong acids, strong bases, and soluble ionic salts) are dissociated into their ions. This more accurately reflects the species that are found in the reaction mixture: Ag + (aq) + NO 3 (aq) + K + (aq) + Cl (aq) AgCl(s) + K + (aq) + NO 3 (aq)

17 Aqueous Reactions © 2012 Pearson Education, Inc. Net Ionic Equation To form the net ionic equation, cross out anything that does not change from the left side of the equation to the right: Ag + (aq) + NO 3 (aq) + K + (aq) + Cl (aq) AgCl(s) + K + (aq) + NO 3 (aq) What is the name of the ions that we cross out on both sides of the equation? And why do we cross them out?

18 Aqueous Reactions © 2012 Pearson Education, Inc. Net Ionic Equation To form the net ionic equation, cross out anything that does not change from the left side of the equation to the right. The only things left in the equation are those things that change (i.e., react) during the course of the reaction: Ag + (aq) + Cl (aq) AgCl(s) This is your net ionic equation. The equation that shows only the ions and molecules directly involved in the reaction.

19 Aqueous Reactions © 2012 Pearson Education, Inc. Writing Net Ionic Equations 1.Write a balanced molecular equation. 2.Dissociate all strong electrolytes. 3.Cross out anything that remains unchanged from the left side to the right side of the equation. 4.Write the net ionic equation with the species that remain.

20 Aqueous Reactions © 2012 Pearson Education, Inc. Acids The Swedish physicist and chemist S. A. Arrhenius defined acids as substances that increase the concentration of H + when dissolved in water. Both the Danish chemist J. N. Brønsted and the British chemist T. M. Lowry defined them as proton donors. Lewis defined them as electron acceptors.

21 Aqueous Reactions © 2012 Pearson Education, Inc. Acids There are only seven strong acids: Hydrochloric (HCl) Hydrobromic (HBr) Hydroiodic (HI) Nitric (HNO 3 ) Sulfuric (H 2 SO 4 ) Chloric (HClO 3 ) Perchloric (HClO 4 )

22 Aqueous Reactions Acids Molecules of different acids ionize to form different numbers of H + ions. –Monoprotic Acids (yield one H + ion per acid) –Diprotic Acids (yields 2 H + ions per acid) Polyprotic Acids ionize in steps H 2 SO 4 (aq) H + (aq) + HSO 4 - (aq) HSO 4 - (aq) H + (aq) + SO 4 2- (aq) © 2012 Pearson Education, Inc.

23 Aqueous Reactions Acids Ionizable Hydrogens © 2012 Pearson Education, Inc. How many hydrogen ions can be generated by each citric acid molecule dissolved in water?

24 Aqueous Reactions © 2012 Pearson Education, Inc. Bases Arrhenius defined bases as substances that increase the concentration of OH when dissolved in water. Brønsted and Lowry defined them as proton acceptors. Lewis defined them as electron donors.

25 Aqueous Reactions © 2012 Pearson Education, Inc. Bases The strong bases are the soluble metal salts of hydroxide ion: Alkali metals Calcium Strontium Barium

26 Aqueous Reactions © 2012 Pearson Education, Inc. Acid-Base Reactions In an acid–base reaction, the acid donates a proton (H + ) to the base. Label Acid, Base, Conjugate Acid, and Conjugate Base

27 Aqueous Reactions Reactivity of Strong and Weak Acids/Bases When reactivity depends only on H + (aq) concentrations, strong acids are more reactive than weak acids. The reactivity of an acid, however, can depend on the anion concentration. –HF is a weak acid, but it is very reactive and attacks many substances. © 2012 Pearson Education, Inc.

28 Aqueous Reactions Comparing Acid Strengths The following represent aqueous solutions of acids HX, HY, and Hz, with water molecules omitted. Rank the acids from strongest to weakest. © 2012 Pearson Education, Inc.

29 Aqueous Reactions Identifying Strong/Weak Electrolytes Classify the following as strong, weak, or nonelectrolyte: –CaCl 2, HNO 3, C 2 H 5 OH (ethanol), HCOOH (formic acid), KOH © 2012 Pearson Education, Inc. Rank the following compounds that are dissolved in water in order of increasing electrical conductivity: Ca(NO 3 ) 2, C 6 H 12 O 6, NaCH 3 COO, CH 3 COOH

30 Aqueous Reactions © 2012 Pearson Education, Inc. Neutralization Reactions Generally, when solutions of an acid and a metal hydroxide base are combined, the products are a salt and water: CH 3 COOH(aq) + NaOH(aq) NaCH 3 COO(aq) + H 2 O(l)

31 Aqueous Reactions © 2012 Pearson Education, Inc. Neutralization Reactions When a strong acid reacts with a strong base, the net ionic equation is HCl(aq) + NaOH(aq) NaCl(aq) + H 2 O(l)

32 Aqueous Reactions © 2012 Pearson Education, Inc. Neutralization Reactions When a strong acid reacts with a strong base, the net ionic equation is HCl(aq) + NaOH(aq) NaCl(aq) + H 2 O(l) H + (aq) + Cl (aq) + Na + (aq) + OH (aq) Na + (aq) + Cl (aq) + H 2 O(l)

33 Aqueous Reactions © 2012 Pearson Education, Inc. Neutralization Reactions When a strong acid reacts with a strong base, the net ionic equation is HCl(aq) + NaOH(aq) NaCl(aq) + H 2 O(l) H + (aq) + Cl (aq) + Na + (aq) + OH (aq) Na + (aq) + Cl (aq) + H 2 O(l) H + (aq) + OH (aq) H 2 O(l)

34 Aqueous Reactions Neutralization Reactions What happens if the base is not water- soluble? Mg(OH) 2 (s) + 2HCl (aq) MgCl 2 (aq) + 2H 2 O (l) © 2012 Pearson Education, Inc.

35 Aqueous Reactions © 2012 Pearson Education, Inc. Gas-Forming Reactions Some metathesis reactions do not give the product expected. In this reaction, the expected product (H 2 CO 3 ) decomposes to give a gaseous product (CO 2 ): CaCO 3 (s) + HCl(aq) CaCl 2 (aq) + CO 2 (g) + H 2 O(l)

36 Aqueous Reactions © 2012 Pearson Education, Inc. Gas-Forming Reactions When a carbonate or bicarbonate reacts with an acid, the products are a salt, carbon dioxide, and water: CaCO 3 (s) + HCl(aq) CaCl 2 (aq) + CO 2 (g) + H 2 O(l) NaHCO 3 (aq) + HBr(aq) NaBr(aq) + CO 2 (g) + H 2 O(l)

37 Aqueous Reactions © 2012 Pearson Education, Inc. Gas-Forming Reactions Similarly, when a sulfite reacts with an acid, the products are a salt, sulfur dioxide, and water: SrSO 3 (s) + 2HI(aq) SrI 2 (aq) + SO 2 (g) + H 2 O(l)

38 Aqueous Reactions © 2012 Pearson Education, Inc. Gas-Forming Reactions This reaction gives the predicted product, but you had better carry it out in the hood, or you will be very unpopular! But just as in the previous examples, a gas is formed as a product of this reaction: Na 2 S(aq) + H 2 SO 4 (aq) Na 2 SO 4 (aq) + H 2 S(g)

39 Aqueous Reactions © 2012 Pearson Education, Inc. Oxidation-Reduction Reactions 2Ca (s) + O 2 (g) 2CaO (s) An oxidation occurs when an atom or ion loses electrons. A reduction occurs when an atom or ion gains electrons. One cannot occur without the other.

40 Aqueous Reactions © 2012 Pearson Education, Inc. Oxidation Numbers To determine if an oxidation–reduction reaction has occurred, we assign an oxidation number (or you may hear oxidation state) to each element in a neutral compound or charged entity. Of course there are rules!

41 Aqueous Reactions © 2012 Pearson Education, Inc. Oxidation Numbers The Rules Elements in their elemental form have an oxidation number of 0. –This includes diatomics The oxidation number of a monatomic ion is the same as its charge. –Alkali metals always have +1 –Alkaline earth metals always have +2 –Aluminum is always +3

42 Aqueous Reactions © 2012 Pearson Education, Inc. Oxidation Numbers The Rules Nonmetals tend to have negative oxidation numbers, although some are positive in certain compounds or ions. –Oxygen has an oxidation number of 2, except in the peroxide ion, in which it has an oxidation number of 1. –Hydrogen is 1 when bonded to a metal, but it is usually +1 because its typically bonded to a nonmetal.

43 Aqueous Reactions © 2012 Pearson Education, Inc. Oxidation Numbers The Rules Nonmetals tend to have negative oxidation numbers, although some are positive in certain compounds or ions. –Fluorine always has an oxidation number of 1. –The other halogens have an oxidation number of 1 when they are negative; they can have positive oxidation numbers, however, most notably in oxyanions.

44 Aqueous Reactions © 2012 Pearson Education, Inc. Oxidation Numbers The Rules The sum of the oxidation numbers in a neutral compound is 0. The sum of the oxidation numbers in a polyatomic ion is the charge on the ion.

45 Aqueous Reactions © 2012 Pearson Education, Inc. Displacement Reactions In displacement reactions, ions oxidize an element. The ions, then, are reduced.

46 Aqueous Reactions Displacement Reactions Mg (s) + 2 HCl (aq) MgCl 2 (aq) + H 2 (g) © 2012 Pearson Education, Inc. 0 +1 -1 +2 -1 0

47 Aqueous Reactions © 2012 Pearson Education, Inc. Displacement Reactions In this reaction, silver ions oxidize copper metal: Cu(s) + 2Ag + (aq) Cu 2+ (aq) + 2Ag(s)

48 Aqueous Reactions © 2012 Pearson Education, Inc. Displacement Reactions The reverse reaction, however, does not occur: Cu 2+ (aq) + 2Ag(s) Cu(s) + 2Ag + (aq) x

49 Aqueous Reactions © 2012 Pearson Education, Inc. Activity Series

50 Aqueous Reactions Analyzing Chemical Reactions for Patterns Imperative to recognize/identify patterns in reactions so that you gain a chemical intuition. Helpful questions can help you determine the reaction: –What are the reactants? –Are they electrolytes or nonelectrolytes? –Are they acids and bases? –Will metathesis produce a ppt? Water? Gas? –Do reactants engage in redox? © 2012 Pearson Education, Inc.

51 Aqueous Reactions © 2012 Pearson Education, Inc. Molarity Two solutions can contain the same compounds but be quite different because the proportions of those compounds are different. Molarity is one way to measure the concentration of a solution: moles of solute volume of solution in liters Molarity (M) =

52 Aqueous Reactions © 2012 Pearson Education, Inc. Mixing a Solution To create a solution of a known molarity, one weighs out a known mass (and, therefore, number of moles) of the solute. The solute is added to a volumetric flask, and solvent is added to the line on the neck of the flask.

53 Aqueous Reactions © 2012 Pearson Education, Inc. Dilution One can also dilute a more concentrated solution by –Using a pipet to deliver a volume of the solution to a new volumetric flask, and –Adding solvent to the line on the neck of the new flask.

54 Aqueous Reactions © 2012 Pearson Education, Inc. Dilution The molarity of the new solution can be determined from the equation M c V c = M d V d, where M c and M d are the molarity of the concentrated and dilute solutions, respectively, and V c and V d are the volumes of the two solutions.

55 Aqueous Reactions © 2012 Pearson Education, Inc. Using Molarities in Stoichiometric Calculations

56 Aqueous Reactions © 2012 Pearson Education, Inc. Titration Titration is an analytical technique in which one can calculate the concentration of a solute in a solution.

57 Aqueous Reactions Titration © 2012 Pearson Education, Inc.

58 Aqueous Reactions Titration 45.7 mL of 0.500 M H 2 SO 4 is required to neutralize 20.0 mL of NaOH solution. What is the concentration of the NaOH solution? © 2012 Pearson Education, Inc.

59 Aqueous Reactions Titration Ag + (aq) + Cl - (aq) AgCl (s) How many grams of chloride ion are in a sample of the water if 20.2 mL of 0.100 M Ag + is needed to react with all the chloride in the sample? If the sample has a mass of 10.0 g, what percent Cl - does it contain? © 2012 Pearson Education, Inc.

60 Aqueous Reactions Chapter 4 Homework Problems 1-4, 7-9, 11-13, 15, 17, 19, 21-23, 25, 27, 29, 30, 32, 33, 35, 36, 38-40, 42, 43, 46-49, 51-53, 55, 57, 58, 60, 61, 63, 65, 67, 69, 71, 73, 75, 77, 79, 81, 83, 85, 87, 89, 94b, 97 © 2012 Pearson Education, Inc.


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