Reactions in Aqueous Solutions 1

Solutions (textbook p ) Aqueous Solution – A solution in which the solvent is water. Water is the solvent (does the dissolving). Water will dissolve polar molecules and ionic compounds. Solutes that are dissolved in water form ions (charged atoms/polyatomic ions). Double displacement reactions have ions that may react with one another. These reactions can form a precipitate, water, or a gas. 2

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Ionization – process of water dissolving polar molecules. The water pulls the polar molecule apart and forms ions. Acids go through ionization and form H + ions. H + ions form hydronium ions, H 3 O + HCl (aq) + H 2 O (l) → H 3 O + (aq) + Cl - (aq) 4

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Dissociation – ionic compounds are separated by the polar molecules into ions. NaOH (aq) → Na + (aq) + OH - (aq) Dissociation of NaCl 6

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Ionic Equations Chemical Equation – shows the reactants and products in a chemical reaction. 2NaOH (aq) + CuCl 2(aq) → 2NaCl (aq) + Cu(OH) 2(s) Complete Ionic equations show the substances as they exist as ions in solution. 2Na + (aq) + 2OH - (aq) + Cu 2+ (aq) + 2Cl - (aq) → 2Na + (aq) + 2Cl - (aq) + Cu(OH) 2(s) 8

Spectator ions – ions that do not participate in the reaction. They are found on both sides of the equation. 2Na + (aq) + 2OH - (aq) + Cu 2+ (aq) + 2Cl - (aq) → 2Na + (aq) + 2Cl - (aq) + Cu(OH) 2(s) Net Ionic Equation – Includes only the particles that participate in the reaction. 2OH - (aq) + Cu 2+ (aq) → Cu(OH) 2(s) 9

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Forming a Precipitate The net ionic equation results in an insoluble compound. This insoluble compound is a precipitate. There are guidelines to determine if the compound is soluble or insoluble. 12

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Forming Water Double displacement reaction sometimes produces water. Increases the number of solvent particles. There is no real observable evidence of this type of reaction because water is colorless and odorless. Usually a neutralization reaction between an acid and a base. This reaction forms a salt and water. 17

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) Neutralization Reaction Movie 18

Forming a Gas Double displacement reactions can form gases. Nonpolar gases such as carbon dioxide (CO 2 ), Hydrogen cyanide (HCN), and hydrogen sulfide (H 2 S) 2HI (aq) + Li 2 S (aq) → H 2 S (g) + 2LiI (aq) 2H + (aq) + 2I - (aq) + 2Li + (aq) + S 2- (aq) → H 2 S (g) + 2Li + (aq) + 2I - (aq) 2H + (aq) + S 2- (aq) → H 2 S (g) 19

Carbonate (CO 3 2- )and bicarbonate (HCO 3 - ) react with acids to form carbon dioxide gas. Carbonic acid (H 2 CO 3 ) is formed in a double displacement reaction. The unstable carbonic acid decomposes into carbon dioxide and water. 20

HCl (aq) + NaHCO 3(aq) → H 2 CO 3(aq) + NaCl (aq) H 2 CO 3(aq) → H 2 O (l) + CO 2(g) Overall : HCl (aq) + NaHCO 3(aq) → H 2 O (l) + CO 2(g) + NaCl (aq) H + (aq) + Cl - (aq) + Na + (aq) + HCO 3 - (aq) → H 2 O (l) + CO 2(g) + Na + (aq) + Cl - (aq) H + (aq) + HCO 3 - (aq) → H 2 O (l) + CO 2(g) 21

Examples HBr (aq) + KOH (aq) → ? H + (aq) + Br - (aq) + K + (aq) + OH - (aq) → H 2 O (l) + K + (aq) + Br - (aq) H + (aq) + OH - (aq) → H 2 O (l) 22

HNO 3 (aq) + Na 2 CO 3 (aq) → ? 2HNO 3 (aq) + Na 2 CO 3 (aq) → H 2 CO 3 (aq) + 2NaNO 3 (aq) But H 2 CO 3 will decompose into CO 2 + H 2 O 2H + (aq) +2NO 3 - (aq) +2Na + (aq) +CO 3 2- (aq) → H 2 O (l) + CO 2 (g) +2Na + (aq) +2NO 3 - (aq) 2H + (aq) + CO 3 2- (aq) → H 2 O (l) + CO 2 (g) 23

19.Aqueous solutions of barium chloride and sodium fluoride are mixed to form a precipitate of barium fluoride. 24

20.Aqueous solutions of copper(I) nitrate and potassium sulfide are mixed to form insoluble copper(I) sulfide. 25

21.Hydrobromic acid (HBr) reacts with aqueous lithium hydroxide. 26

22.Hydrochloric acid reacts with aqueous lithium cyanide. 27

23.Perchloric acid (HClO 4 ) reacts with aqueous rubidium hydroxide. 28