Chapter 4 Aqueous Reactions and Solution Stoichiometry

Chapter 4 Aqueous Reactions and Solution Stoichiometry

Chemistry, The Central Science, 11th edition Theodore L. Brown; H. Eugene LeMay, Jr.; and Bruce E. Bursten Chapter 4 Aqueous Reactions and Solution Stoichiometry John D. Bookstaver St. Charles Community College Cottleville, MO Aqueous Reactions

2009, Prentice-Hall, Inc. Solutions Solutions are defined as homogeneous mixtures of two or more pure substances. The solvent is present in greatest abundance. All other substances are solutes. Aqueous Reactions

2009, Prentice-Hall, 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. Aqueous Reactions

2009, Prentice-Hall, Inc. Dissociation An electrolyte is a substances that dissociates into ions when dissolved in water. Aqueous Reactions 2009, Prentice-Hall, Inc.

Electrolytes 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 Aqueous so. Reactions

2009, Prentice-Hall, Inc. Electrolytes and Nonelectrolytes Soluble ionic compounds tend to be electrolytes. Aqueous Reactions 2009, Prentice-Hall, Inc.

Electrolytes and Nonelectrolytes Molecular compounds tend to be nonelectrolytes, except for acids and bases. Aqueous Reactions 2009, Prentice-Hall, Inc. Electrolytes

A strong electrolyte dissociates completely when dissolved in water. A weak electrolyte only dissociates partially when dissolved in water. Aqueous Reactions 2009, Prentice-Hall, Inc. Strong Electrolytes Are

Strong acids Strong bases Aqueous Reactions 2009, Prentice-Hall, Inc. Strong Electrolytes Are Strong acids Strong bases Soluble ionic salts Aqueous

Reactions 2009, Prentice-Hall, Inc. Precipitation Reactions When one mixes ions that form compounds that are insoluble (as could be predicted by the solubility guidelines), a precipitate is formed. Aqueous

Reactions 2009, Prentice-Hall, Inc. Metathesis (Exchange) Reactions Metathesis comes from a Greek word that means to transpose. AgNO3 (aq) + KCl (aq) AgCl (s) + KNO3 (aq) Aqueous Reactions 2009, Prentice-Hall, Inc. Metathesis (Exchange) Reactions

Metathesis comes from a Greek word that means to transpose. It appears the ions in the reactant compounds exchange, or transpose, ions. AgNO3 (aq) + KCl (aq) AgCl (s) + KNO3 (aq) Aqueous Reactions 2009, Prentice-Hall, 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. Aqueous Reactions 2009, Prentice-Hall, Inc. Molecular Equation The molecular equation lists the reactants and products in their molecular form.

AgNO3 (aq) + KCl (aq) AgCl (s) + KNO3 (aq) Aqueous Reactions 2009, Prentice-Hall, Inc. Ionic Equation In the 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) + NO3- (aq) + K+ (aq) + Cl- (aq)

AgCl (s) + K+ (aq) + NO3- (aq) Aqueous Reactions 2009, Prentice-Hall, 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) + NO3-(aq) + K+(aq) + Cl-(aq) AgCl (s) + K+(aq) + NO3-(aq) Aqueous Reactions 2009, Prentice-Hall, 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) Aqueous Reactions 2009, Prentice-Hall, 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. Those things that didnt change (and were deleted from the net ionic equation) are called + + Ag (aq) + NO (aq) + K (aq)

+ Cl (aq) spectator ions. 3 AgCl (s) + K+(aq) + NO3-(aq) Aqueous Reactions 2009, Prentice-Hall, 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. Aqueous Reactions 2009, Prentice-Hall, Inc. Acids Arrhenius defined acids as substances that increase the

concentration of H+ when dissolved in water. Brnsted and Lowry defined them as proton donors. Aqueous Reactions 2009, Prentice-Hall, Inc. Acids There are only seven strong acids:

Hydrochloric (HCl) Hydrobromic (HBr) Hydroiodic (HI) Nitric (HNO3) Sulfuric (H2SO4) Chloric (HClO3) Perchloric (HClO4)

Aqueous Reactions 2009, Prentice-Hall, Inc. Bases Arrhenius defined bases as substances that increase the concentration of OH when dissolved in water. Brnsted and Lowry defined them as proton

acceptors. Aqueous Reactions 2009, Prentice-Hall, Inc. Bases The strong bases are the soluble metal salts of hydroxide ion:

Alkali metals Calcium Strontium Barium Aqueous Reactions 2009, Prentice-Hall, Inc. Acid-Base Reactions In an acid-base

reaction, the acid donates a proton (H+) to the base. Aqueous Reactions 2009, Prentice-Hall, Inc. Neutralization Reactions Generally, when solutions of an acid and a base are combined, the products are a salt and water. CH3COOH (aq) + NaOH (aq) CH3COONa (aq) +

H2O (l) Aqueous Reactions 2009, Prentice-Hall, Inc. Neutralization Reactions When a strong acid reacts with a strong base, the net ionic equation is HCl (aq) + NaOH (aq) NaCl (aq) + H2O (l) Aqueous Reactions

2009, Prentice-Hall, Inc. Neutralization Reactions When a strong acid reacts with a strong base, the net ionic equation is HCl (aq) + NaOH (aq) NaCl (aq) + H2O (l) H+ (aq) + Cl- (aq) + Na+ (aq) + OH-(aq) Na+ (aq) + Cl- (aq) + H2O (l) Aqueous Reactions 2009, Prentice-Hall, Inc. Neutralization Reactions

When a strong acid reacts with a strong base, the net ionic equation is HCl (aq) + NaOH (aq) NaCl (aq) + H2O (l) H+ (aq) + Cl- (aq) + Na+ (aq) + OH-(aq) Na+ (aq) + Cl- (aq) + H2O (l) H+ (aq) + OH- (aq) H2O (l) Aqueous Reactions 2009, Prentice-Hall, Inc. Gas-Forming Reactions Some metathesis reactions do not give

the product expected. In this reaction, the expected product (H2CO3) decomposes to give a gaseous product (CO2). CaCO3 (s) + HCl (aq) CaCl2 (aq) + CO2 (g) + H2O (l) Aqueous Reactions 2009, Prentice-Hall, Inc. Gas-Forming Reactions When a carbonate or bicarbonate reacts with an acid, the products are a

salt, carbon dioxide, and water. CaCO3 (s) + HCl (aq) CaCl2 (aq) + CO2 (g) + H2O (l) NaHCO3 (aq) + HBr (aq) NaBr (aq) + CO2 (g) + H2O (l) Aqueous Reactions 2009, Prentice-Hall, Inc. Gas-Forming Reactions Similarly, when a sulfite reacts with an acid, the products are a salt, sulfur dioxide, and water.

SrSO3 (s) + 2 HI (aq) SrI2 (aq) + SO2 (g) + H2O (l) Aqueous Reactions 2009, Prentice-Hall, 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 a product of this

Na2gas S (aq)is+formed H2SO4 as (aq) Na2SO4 (aq) + H2S (g) reaction. Aqueous Reactions 2009, Prentice-Hall, Inc. Oxidation-Reduction Reactions 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. Aqueous Reactions 2009, Prentice-Hall, Inc. Oxidation Numbers To determine if an oxidation-reduction reaction has occurred, we assign an oxidation number to each element in a

neutral compound or charged entity. Aqueous Reactions 2009, Prentice-Hall, Inc. Oxidation Numbers Elements in their elemental form have an oxidation number of 0. The oxidation number of a monatomic ion is the same as its charge. Aqueous

Reactions 2009, Prentice-Hall, Inc. Oxidation Numbers 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, +1 when bonded to a nonmetal. Aqueous

Reactions 2009, Prentice-Hall, Inc. Oxidation Numbers 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.

Aqueous Reactions 2009, Prentice-Hall, Inc. Oxidation Numbers 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. Aqueous

Reactions 2009, Prentice-Hall, Inc. Displacement Reactions In displacement reactions, ions oxidize an element. The ions, then, are reduced. Aqueous Reactions

2009, Prentice-Hall, Inc. Displacement Reactions In this reaction, silver ions oxidize copper metal. Cu (s) + 2 Ag+ (aq) Cu2+ (aq) + 2 Ag (s) Aqueous Reactions 2009, Prentice-Hall, Inc. Displacement Reactions

The reverse reaction, however, does not occur. Cu2+ (aq) + 2 Ag (s) x Cu (s) + 2 Ag+ (aq) Aqueous Reactions 2009, Prentice-Hall, Inc. Activity Series Aqueous

Reactions 2009, Prentice-Hall, 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. Molarity (M) = moles of solute

volume of solution in liters Aqueous Reactions 2009, Prentice-Hall, 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. Aqueous Reactions 2009, Prentice-Hall, 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.

Aqueous Reactions 2009, Prentice-Hall, Inc. Dilution The molarity of the new solution can be determined from the equation Mc Vc = Md Vd, where Mc and Md are the molarity of the concentrated and dilute solutions, respectively, and Vc and Vd are the volumes of the two solutions.

Aqueous Reactions 2009, Prentice-Hall, Inc. Using Molarities in Stoichiometric Calculations Aqueous Reactions 2009, Prentice-Hall, Inc. Titration Titration is an

analytical technique in which one can calculate the concentration of a solute in a solution. Aqueous Reactions 2009, Prentice-Hall, Inc.

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