Reactions in Aqueous Solution Chapter 4 Copyright The

Reactions in Aqueous Solution Chapter 4 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

A solution is a homogenous mixture of 2 or more substances The solute is(are) the substance(s) present in the smaller amount(s) The solvent is the substance present in the larger amount Solution Solvent Solute Soft drink (l) H 2 O Sugar, CO 2 Air (g) N 2 O 2, Ar, CH 4 Soft Solder (s) Pb Sn aqueous solutions of KMn. O 4 2

An electrolyte is a substance that, when dissolved in water, results in a solution that can conduct electricity. A nonelectrolyte is a substance that, when dissolved, results in a solution that does not conduct electricity. nonelectrolyte weak electrolyte strong electrolyte 3

Conduct electricity in solution? Cations (+) and Anions (-) Strong Electrolyte – 100% dissociation Na. Cl (s) H 2 O Na+ (aq) + Cl- (aq) Weak Electrolyte – not completely dissociated CH 3 COOH CH 3 COO- (aq) + H+ (aq) 4

Ionization of acetic acid CH 3 COOH CH 3 COO- (aq) + H+ (aq) A reversible reaction. The reaction can occur in both directions. Acetic acid is a weak electrolyte because its ionization in water is incomplete. 5

Hydration is the process in which an ion is surrounded by water molecules arranged in a specific manner. d- d+ H 2 O 6

Nonelectrolyte does not conduct electricity? No cations (+) and anions (-) in solution H 2 O C 6 H 12 O 6 (s) C 6 H 12 O 6 (aq) 7

Precipitation Reactions Precipitate – insoluble solid that separates from solution precipitate Pb(NO 3)2 (aq) + 2 Na. I (aq) Pb. I 2 (s) + 2 Na. NO 3 (aq) molecular equation Pb 2+ + 2 NO 3 - + 2 Na+ + 2 I- Pb. I 2 (s) + 2 Na+ + 2 NO 3 ionic equation Pb. I 2 Pb 2+ + 2 I- Pb. I 2 (s) net ionic equation Na+ and NO 3 - are spectator ions 8

Precipitation of Lead Iodide Pb 2+ + 2 I- Pb. I 2 (s) Pb. I 2 9

Solubility is the maximum amount of solute that will dissolve in a given quantity of solvent at a specific temperature. 10

Examples of Insoluble Compounds Cd. S Pb. S Ni(OH)2 Al(OH)3 11

Writing Net Ionic Equations 1. Write the balanced molecular equation. 2. Write the ionic equation showing the strong electrolytes completely dissociated into cations and anions. 3. Cancel the spectator ions on both sides of the ionic equation 4. Check that charges and number of atoms are balanced in the net ionic equation Write the net ionic equation for the reaction of silver nitrate with sodium chloride. Ag. NO 3 (aq) + Na. Cl (aq) Ag. Cl (s) + Na. NO 3 (aq) Ag+ + NO 3 - + Na+ + Cl- Ag. Cl (s) + Na+ + NO 3 - Ag+ + Cl- Ag. Cl (s) 12

Chemistry In Action: An Undesirable Precipitation Reaction Ca 2+ (aq) + 2 HCO 3 - (aq) Ca. CO 3 (s) + CO 2 (aq) + H 2 O (l) CO 2 (aq) CO 2 (g) 13

Properties of Acids Have a sour taste. Vinegar owes its taste to acetic acid. Citrus fruits contain citric acid. Cause color changes in plant dyes. React with certain metals to produce hydrogen gas. 2 HCl (aq) + Mg (s) Mg. Cl 2 (aq) + H 2 (g) React with carbonates and bicarbonates to produce carbon dioxide gas 2 HCl (aq) + Ca. CO 3 (s) Ca. Cl 2 (aq) + CO 2 (g) + H 2 O (l) Aqueous acid solutions conduct electricity. 14

Properties of Bases Have a bitter taste. Feel slippery. Many soaps contain bases. Cause color changes in plant dyes. Aqueous base solutions conduct electricity. Examples: 15

Arrhenius acid is a substance that produces H+ (H 3 O+) in water Arrhenius base is a substance that produces OH- in water 16

Hydronium ion, hydrated proton, H 3 O+ 17

A Brønsted acid is a proton donor A Brønsted base is a proton acceptor base acid base A Brønsted acid must contain at least one ionizable proton! 18

Monoprotic acids HCl H+ + Cl- Strong electrolyte, strong acid HNO 3 H+ + NO 3 - Strong electrolyte, strong acid CH 3 COOH H+ + CH 3 COO- Weak electrolyte, weak acid Diprotic acids H 2 SO 4 H+ + HSO 4 - Strong electrolyte, strong acid HSO 4 - H+ + SO 42 - Weak electrolyte, weak acid Triprotic acids H 3 PO 4 H+ + H 2 PO 4 - H+ + HPO 42 - H+ + PO 43 - Weak electrolyte, weak acid 19

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Identify each of the following species as a Brønsted acid, base, or both. (a) HI, (b) CH 3 COO-, (c) H 2 PO 4 - HI (aq) H+ (aq) + I- (aq) Brønsted acid CH 3 COO- (aq) + H+ (aq) CH 3 COOH (aq) Brønsted base H 2 PO 4 - (aq) H+ (aq) + HPO 42 - (aq) Brønsted acid H 2 PO 4 - (aq) + H+ (aq) H 3 PO 4 (aq) Brønsted base 21

Neutralization Reaction acid + base salt + water HCl (aq) + Na. OH (aq) Na. Cl (aq) + H 2 O H+ + Cl- + Na+ + OH- Na+ + Cl- + H 2 O H+ + OH- H 2 O 22

Neutralization Reaction Involving a Weak Electrolyte weak acid + base salt + water HCN (aq) + Na. OH (aq) Na. CN (aq) + H 2 O HCN + Na+ + OH- Na+ + CN- + H 2 O HCN + OH- CN- + H 2 O 23

Neutralization Reaction Producing a Gas acid + base salt + water + CO 2 2 HCl (aq) + Na 2 CO 3 (aq) 2 Na. Cl (aq) + H 2 O +CO 2 2 H+ + 2 Cl- + 2 Na+ + CO 32 - 2 Na+ + 2 Cl- + H 2 O + CO 2 2 H+ + CO 32 - H 2 O + CO 2 24

Oxidation-Reduction Reactions (electron transfer reactions) 2 Mg 2+ + 4 e- Oxidation half-reaction (lose e-) O 2 + 4 e- 2 O 2 Reduction half-reaction (gain e-) 2 Mg + O 2 + 4 e- 2 Mg 2+ + 2 O 2 - + 4 e 25 2 Mg + O 2 2 Mg. O

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Zn (s) + Cu. SO 4 (aq) Zn. SO 4 (aq) + Cu (s) Zn 2+ + 2 e- Zn is oxidized Zn is the reducing agent Cu 2+ + 2 e- Cu Cu 2+ is reduced Cu 2+ is the oxidizing agent Copper wire reacts with silver nitrate to form silver metal. What is the oxidizing agent in the reaction? Cu (s) + 2 Ag. NO 3 (aq) Cu(NO 3)2 (aq) + 2 Ag (s) Cu 2+ + 2 e. Ag+ + 1 e- Ag Ag+ is reduced Ag+ is the oxidizing agent 27

Oxidation number The charge the atom would have in a molecule (or an ionic compound) if electrons were completely transferred. 1. Free elements (uncombined state) have an oxidation number of zero. Na, Be, K, Pb, H 2, O 2, P 4 = 0 2. In monatomic ions, the oxidation number is equal to the charge on the ion. Li+, Li = +1; Fe 3+, Fe = +3; O 2 -, O = -2 3. The oxidation number of oxygen is usually – 2. In H 2 O 2 and O 22 - it is – 1. 28 4. 4

4. The oxidation number of hydrogen is +1 except when it is bonded to metals in binary compounds. In these cases, its oxidation number is – 1. 5. Group IA metals are +1, IIA metals are +2 and fluorine is always – 1. 6. The sum of the oxidation numbers of all the atoms in a molecule or ion is equal to the charge on the molecule or ion. 7. Oxidation numbers do not have to be integers. Oxidation number of oxygen in the superoxide ion, O 2, is –½. - HCO 3 What are the oxidation numbers of all the elements in HCO 3 - ? O = – 2 H = +1 3 x(– 2) + 1 + ? = – 1 C = +4 29

The Oxidation Numbers of Elements in their Compounds 30

What are the oxidation numbers of all the elements in each of these compounds? Na. IO 3 IF 7 K 2 Cr 2 O 7 Na. IO 3 Na = +1 O = -2 3 x(-2) + 1 + ? = 0 I = +5 IF 7 F = -1 7 x(-1) + ? = 0 I = +7 K 2 Cr 2 O 7 O = -2 K = +1 7 x(-2) + 2 x(+1) + 2 x(? ) = 0 Cr = +6 31

Types of Oxidation-Reduction Reactions Combination Reaction A + B C 0 +3 -1 0 2 Al + 3 Br 2 2 Al. Br 3 Decomposition Reaction C A + B +1 +5 -2 +1 -1 0 2 KCl. O 3 2 KCl + 3 O 2 32

Types of Oxidation-Reduction Reactions Combustion Reaction A + O 2 B 0 0 +4 -2 S + O 2 SO 2 0 0 +2 -2 2 Mg + O 2 2 Mg. O 33

Types of Oxidation-Reduction Reactions Displacement Reaction A + BC AC + B 0 +1 +2 0 Sr + 2 H 2 O Sr(OH)2 + H 2 Hydrogen Displacement +4 0 0 +2 Ti. Cl 4 + 2 Mg Ti + 2 Mg. Cl 2 Metal Displacement 0 -1 -1 0 Cl 2 + 2 KBr 2 KCl + Br 2 Halogen Displacement 34

The Activity Series for Metals Hydrogen Displacement Reaction M + BC MC + B M is metal BC is acid or H 2 O B is H 2 Ca + 2 H 2 O Ca(OH)2 + H 2 Pb + 2 H 2 O Pb(OH)2 + H 2 35

The Activity Series for Halogens F 2 > Cl 2 > Br 2 > I 2 Halogen Displacement Reaction 0 -1 -1 0 Cl 2 + 2 KBr 2 KCl + Br 2 I 2 + 2 KBr 2 KI + Br 2 36

Types of Oxidation-Reduction Reactions Disproportionation Reaction The same element is simultaneously oxidized and reduced. Example: reduced +1 0 -1 Cl 2 + 2 OH- Cl. O- + Cl- + H 2 O oxidized 37

Classify each of the following reactions. Ca 2+ + CO 32 - Ca. CO 3 Precipitation NH 3 + H+ NH 4+ Acid-Base Zn + 2 HCl Zn. Cl 2 + H 2 Redox (H 2 Displacement) Ca + F 2 Ca. F 2 Redox (Combination) 38

Chemistry in Action: Breath Analyzer +6 3 CH 2 OH + 2 K 2 Cr 2 O 7 + 8 H 2 SO 4 +3 3 CH 3 COOH + 2 Cr 2(SO 4)3 + 2 K 2 SO 4 + 11 H 2 O 39

Solution Stoichiometry The concentration of a solution is the amount of solute present in a given quantity of solvent or solution. M = molarity = moles of solute liters of solution What mass of KI is required to make 500. m. L of a 2. 80 M KI solution? volume of KI solution 500. m. L x 1 L 1000 m. L M KI x moles KI 2. 80 mol KI 1 L soln x M KI 166 g KI 1 mol KI grams KI = 232 g KI 40

Preparing a Solution of Known Concentration 41

Dilution is the procedure for preparing a less concentrated solution from a more concentrated solution. Dilution Add Solvent Moles of solute before dilution (i) = Moles of solute after dilution (f) Mi V i = Mf V f 42

How would you prepare 60. 0 m. L of 0. 200 M HNO 3 from a stock solution of 4. 00 M HNO 3? Mi. Vi = Mf. Vf Mi = 4. 00 M Mf = 0. 200 M Vf = 0. 0600 L Vi = Mf V f Mi Vi = ? L = 0. 200 M x 0. 0600 L = 0. 00300 L = 3. 00 m. L 4. 00 M Dilute 3. 00 m. L of acid with water to a total volume of 60. 0 m. L. 43

Gravimetric Analysis 1. Dissolve unknown substance in water 2. React unknown with known substance to form a precipitate 3. Filter and dry precipitate 4. Weigh precipitate 5. Use chemical formula and mass of precipitate to determine amount of unknown ion 44

Titrations In a titration a solution of accurately known concentration is added gradually added to another solution of unknown concentration until the chemical reaction between the two solutions is complete. Equivalence point – the point at which the reaction is complete Indicator – substance that changes color at (or near) the equivalence point Slowly add base to unknown acid UNTIL the indicator changes color 45

Titrations can be used in the analysis of Acid-base reactions H 2 SO 4 + 2 Na. OH 2 H 2 O + Na 2 SO 4 Redox reactions 5 Fe 2+ + Mn. O 4 - + 8 H+ Mn 2+ + 5 Fe 3+ + 4 H 2 O 46

What volume of a 1. 420 M Na. OH solution is required to titrate 25. 00 m. L of a 4. 50 M H 2 SO 4 solution? WRITE THE CHEMICAL EQUATION! H 2 SO 4 + 2 Na. OH 2 H 2 O + Na 2 SO 4 volume acid 25. 00 m. L x M acid moles red 4. 50 mol H 2 SO 4 1000 m. L soln x rxn coef. moles base 2 mol Na. OH 1 mol H 2 SO 4 x M base volume base 1000 ml soln 1. 420 mol Na. OH = 158 m. L 47

16. 42 m. L of 0. 1327 M KMn. O 4 solution is needed to oxidize 25. 00 m. L of an acidic Fe. SO 4 solution. What is the molarity of the iron solution? WRITE THE CHEMICAL EQUATION! 5 Fe 2+ + Mn. O 4 - + 8 H+ Mn 2+ + 5 Fe 3+ + 4 H 2 O volume red M red moles red 16. 42 m. L = 0. 01642 L x 0. 1327 mol KMn. O 4 1 L rxn coef. moles oxid V oxid M oxid 25. 00 m. L = 0. 02500 L x 5 mol Fe 2+ 1 mol KMn. O 4 x 1 0. 02500 L Fe 2+ = 0. 4358 M 48

Chemistry in Action: Metals from the Sea Ca. CO 3 (s) Ca. O (s) + CO 2 (g) Ca. O (s) + H 2 O (l) Ca 2+ (aq) + 2 OH (aq) Mg 2+ (aq) + 2 OH (aq) Mg(OH) 2 (s) Mg(OH)2 (s) + 2 HCl (aq) Mg. Cl 2 (aq) + 2 H 2 O (l) Mg 2+ + 2 e- Mg 2 Cl- Cl 2 + 2 e. Mg. Cl 2 (aq) Mg (s) + Cl 2 (g) 49