Double-replacement reactions occur between substances in aqueous solutions and produce precipitates, water, or gases. Section 3: Reactions in Aqueous Solutions K What I Know W What I Want to Find Out L What I Learned

10(H) Understand and differentiate among acid-base reactions, precipitation reactions, and oxidation-reduction reactions. 8(D) Use the law of conservation of mass to write and balance chemical equations. 10(A) Describe the unique role of water in chemical and biological systems. 2(I) Communicate valid conclusions supported by the data through methods such as lab reports, labeled drawings, graphs, journals, summaries, oral reports, and technology–based reports. 3(A)In all fields of science, analyze, evaluate, and critique scientific explanations by using empirical evidence, logical reasoning, and experimental and observational testing, including examining all sides of scientific evidence of those scientific explanations, so as to encourage critical thinking by the student. Reactions in Aqueous Solutions Copyright © McGraw-Hill Education

Essential Questions What are aqueous solutions? How are complete ionic and net ionic equations written for chemical reactions in aqueous solutions? How can you predict whether reactions in aqueous solutions will produce a precipitate, water, or a gas? Reactions in Aqueous Solutions Copyright © McGraw-Hill Education

Review solution Reactions in Aqueous Solutions Copyright © McGraw-Hill Education Vocabulary New aqueous solution solute solvent complete ionic equation spectator ion net ionic equation

Aqueous Solutions An aqueous solution contains one or more dissolved substances (called solutes) in water. The solvent is the most plentiful substance in a solution. Water is always the solvent in an aqueous solution. There are many possible solutes—sugar and alcohol are molecular compounds that exist as molecules in aqueous solutions. Compounds that produce hydrogen ions in aqueous solutions are acids. Ionic compounds can also be solutes in aqueous solutions. When ionic compounds dissolve in water, their ions separate in a process called dissociation. Reactions in Aqueous Solutions Copyright © McGraw-Hill Education

Types of Reactions in Aqueous Solutions When two solutions that contain ions as solutes are combined, the ions might react. If they react, it is always a double replacement reaction. Three products can form: precipitates, water, or gases. Aqueous solutions of sodium hydroxide and copper(II) chloride react to form the precipitate copper(II) hydroxide. 2NaOH(aq) + CuCl 2 (aq) → 2NaCl(aq) + Cu(OH) 2 (s) Ionic equations that show all of the particles in a solution as they actually exist are called complete ionic equations. 2Na + (aq) + 2OH – (aq) + Cu 2+ (aq)+ 2Cl – (aq) → 2Na + (aq) + 2Cl – (aq) + Cu(OH) 2 (s) Reactions in Aqueous Solutions Copyright © McGraw-Hill Education

Types of Reactions in Aqueous Solutions Ions that do not participate in a reaction are called spectator ions and are not usually written in ionic equations. Formulas that include only the particles that participate in reactions are called net ionic equations. 2OH – (aq) + Cu 2+ (aq) → Cu(OH) 2 (s) Some reactions produce more water molecules. No evidence of a chemical reaction is observable. HBr(aq) + NaOH(aq) → H 2 O(l) + NaBr(aq) Without spectator ions: H + (aq) + OH – (aq) → H 2 O(l). Reactions in Aqueous Solutions Copyright © McGraw-Hill Education

Reactions in Aqueous Solutions Copyright © McGraw-Hill Education REACTIONS THAT FORM A PRECIPITATE Use with Example Problem 3. Problem Write the chemical, complete ionic, and net ionic equations for the reaction between aqueous solutions of barium nitrate and sodium carbonate that forms the precipitate barium carbonate. Response ANALYZE THE PROBLEM You are given the word equation for the reaction between barium nitrate and sodium carbonate. You must determine the chemical formulas and relative amounts of all reactants and products to write the balanced chemical equation. To write the complete ionic equation, you need to show the ionic states of the reactants and products. By crossing out the spectator ions from the complete ionic equation, you can write the net ionic equation. The net ionic equation will include fewer substances than the other equations. SOLVE FOR THE UNKNOWN Write the correct chemical formulas and physical states for all substances involved in the reaction. Ba(NO 3 ) 2 (aq) + Na 2 CO 3 (aq) → BaCO 3 (s) + NaNO 3 (aq) Balance the skeleton equation. Ba(NO 3 ) 2 (aq) + Na 2 CO 3 (aq) → BaCO 3 (s) + 2NaNO 3 (aq) Show the ions of the reactants and the products. Ba 2+ (aq) + 2NO 3 − (aq) + 2Na + (aq) + CO 3 2− (aq) → BaCO 3 (s) + 2Na + (aq) + 2NO 3 − (aq)

Reactions in Aqueous Solutions Copyright © McGraw-Hill Education REACTIONS THAT FORM A PRECIPITATE EVALUATE THE ANSWER The net ionic equation includes fewer substances than the other equations because it shows only the reacting particles. The particles composing the solid precipitate that is the result of the reaction are no longer ions. SOLVE FOR THE UNKNOWN Cross out the spectator ions from the complete ionic equation. Ba 2+ (aq) + 2NO 3 − (aq) + 2Na + (aq) + CO 3 2− (aq) → BaCO 3 (s) + 2Na + (aq) + 2NO 3 − (aq) Write the net ionic equation. Ba 2+ (aq) + CO 3 2 − → BaCO 3 (s)

Types of Reactions in Aqueous Solutions Gases that are commonly produced are carbon dioxide, hydrogen cyanide, and hydrogen sulfide. 2HI(aq) + Li 2 S(aq) → H 2 S(g) + 2LiI(aq) Another example is mixing vinegar and baking soda, which produces carbon dioxide gas. HCl(aq) + NaHCO 3 (aq) → H 2 CO 3 (aq) + NaCl(aq) H 2 CO 3 (aq) decomposes immediately. H 2 CO 3 (aq) → H 2 O(l) + CO 2 (g) Reactions in Aqueous Solutions Copyright © McGraw-Hill Education

Reactions in Aqueous Solutions Copyright © McGraw-Hill Education REACTIONS THAT FORM WATER Use with Example Problem 4. Problem Write the chemical, complete ionic, and net ionic equations for the reaction between hydrochloric acid and aqueous lithium hydroxide. This reaction produces water and aqueous lithium chloride. Response ANALYZE THE PROBLEM You are given the word equation for the reaction that occurs between hydrochloric acid and aqueous lithium hydroxide to produce water and aqueous lithium chloride. You must determine the chemical formulas for and relative amounts of all reactants and products to write the balanced chemical equation. To write the complete ionic equation, you need to show the ionic states of the reactants and products. By crossing out the spectator ions from the complete ionic equation, you can write the net ionic equation.

Reactions in Aqueous Solutions Copyright © McGraw-Hill Education REACTIONS THAT FORM WATER EVALUATE THE ANSWER The net ionic equation includes fewer substances than the other equations because it shows only those particles involved in the reaction that produces water. The particles that compose the product water are no longer ions.

Reactions in Aqueous Solutions Copyright © McGraw-Hill Education REACTIONS THAT FORM GASES Use with Example Problem 5. Problem Write the chemical, complete ionic, and net ionic equations for the reaction between hydrochloric acid and aqueous sodium sulfide, which produces hydrogen sulfide gas. Response ANALYZE THE PROBLEM You are given the word equation for the reaction between hydrochloric acid (HCl) and sodium sulfide (Na 2 S). You must write the skeleton equation and balance it. To write the complete ionic equation, you need to show the ionic states of the reactants and products. By crossing out the spectator ions in the complete ionic equation, you can write the net ionic equation. SOLVE FOR THE UNKNOWN Write the correct skeleton equation for the reaction. HCl(aq) + Na 2 S(aq) → H 2 S(g) + NaCl(aq) Balance the skeleton equation. 2HCl(aq) + Na 2 S(aq) → H 2 S(g) + 2NaCl(aq) Show the ions of the reactants and the products. 2H + (aq) + 2Cl − (aq) + 2Na + (aq) + S 2− (aq) → H 2 S(g) + 2Na + (aq) + 2Cl − (aq) Cross out the spectator ions from the complete ionic equation. 2H + (aq) + 2Cl − (aq) + 2Na + (aq) + S 2− (aq) → H 2 S(g) + 2Na + (aq) + 2Cl − (aq)

Reactions in Aqueous Solutions Copyright © McGraw-Hill Education REACTIONS THAT FORM GASES EVALUATE THE ANSWER The net ionic equation includes fewer substances than the other equations because it shows only those particles involved in the reaction that produce hydrogen sulfide. The particles that compose the product are no longer ions. SOLVE FOR THE UNKNOWN Write the net ionic equation in its smallest whole-number ratio. 2H + (aq) + S 2- (aq) → H 2 S(g)

Types of Reactions in Aqueous Solutions Two reactions can be combined and represented by a single chemical reaction. Reactions in Aqueous Solutions Copyright © McGraw-Hill Education

Reactions in Aqueous Solutions Copyright © McGraw-Hill Education Review Essential Questions What are aqueous solutions? How are complete ionic and net ionic equations written for chemical reactions in aqueous solutions? How can you predict whether reactions in aqueous solutions will produce a precipitate, water, or a gas? Vocabulary aqueous solution solute spectator ion net ionic equation solvent complete ionic equation