Reactions in Aqueous Solutions

Transcription

1 Copyright 2004 by houghton Mifflin Company. Reactions in Aqueous Solutions Chapter 7 All rights reserved Predicting if a Rxn Will Occur When chemicals are mixed and one of these driving forces can occur, the reaction will generally happen 2 Dissociation anions and cations of an ionic cmpds separate from each other when dissolved in water electrical conductivity is evidence of this dissociation ionic compounds 3

2 4 Electrolytes are substances whose aqueous solution is a conductor of electricity All electrolytes have ions dissolved in water Strong electrolytes: Nonelectrolytes: Weak electrolytes: Dissociation potassium chloride dissociates in water into potassium cations and chloride anions KCl (aq) = K + (aq) + Cl - (aq) K Cl K + Cl - copper(ii) sulfate dissociates in water into copper(ii) cations and sulfate anions CuSO 4(aq) = Cu +2 (aq) + SO 4 2- (aq) 5 Dissociation potassium sulfate dissociates in water into potassium cations and sulfate anions K 2 SO 4(aq) = 2 K + (aq) + SO 4 2- (aq) K SO 4 K K + SO 4 2- K + 6

3 7 At least one of the products formed is insoluble in water KI (aq) + AgNO 3(aq) KNO 3(aq) + AgI (s) K + I - Ag + NO 3 - K + NO 3 - Ag I Solubility Guidelines Soluble Cmpds of alkalai metals, nitrate, acetate & ammonium ions Cmpds of chloride, bromide & iodide ions except lead(ii) ion mercury(i) ion silver ion Cmpds of sulfate ion except strontium ion lead(ii) ion barium ion mercury(i) ion 8 Solubility Guidelines Insoluble Cmpds of hydroxide ions except calcium ion barium ion strontium ion slightly soluble Cmpds of sulfide ions except alkaline earth metals Cmpds of carbonate & phosphate ions 9

4 10 Which of the following would be soluble? NaCl CaCO 3 AgCl Na 3 PO 4 Predicting the Formation of a Precipitate Write reactants as they exist (ionic if aq & soluble) Look for insoluble combinations of ions 11 Which of the following mixtures would result in a precipitation? NaCl + AgNO 3 NH 4 OH + NiCl 2 NaCl + Ca(NO 3 ) Pb(C 2 H 3 O 2 ) 2 + KBr 4 12

5 Ionic Equations Molecular equations: equations which describe the chemicals put into the water & the product molecules KCl (aq) + AgNO 3(aq) KNO 3(aq) + AgCl (s) Complete ionic equations: equations which describe the actual ions & molecules in the solutions as well as the molecules of solid, liquid and gas not dissolved K + (aq) + Cl - (aq)+ Ag + (aq)+ NO 3 - (aq) K + (aq) + NO 3 - (aq) + AgCl (s) 7.3 Ionic Equations Spectator ions: K + (aq) + Cl- (aq) + Ag+ (aq) + NO 3 - (aq) K+ (aq) + NO 3 - (aq) + AgCl (s) net ionic equation: Cl - (aq) + Ag+ (aq) AgCl (s) Acid-Base Reactions If water can pull an H + off of a molecule to produce H 3 O +, then that molecule is considered an acid. HCl (g) + H 2 O (l) H 3 O + (aq) + Cl- (aq) Strong acid: HCl H 2 SO 4 HNO 3 HClO 4 HI HBr 15

6 Acid-Base Reactions A base is a molecule that can pull an H + off of an acid HCl (g) + H 2 O (l) H 3 O + (aq) + Cl - (aq) acid base HF (g) + OH - (aq) H 2 O (l) + F - (aq) acid base Strong base: 7.4 Acid-Base Reactions the cation from the base combines with the anion from the acid to make the salt acid + base salt + water H 2 SO 4(aq) + Ca(OH) 2(aq) CaSO 4(aq) + 2 H 2 O (l) the net ionic equation for an aqueous Acid-Base reaction is always H 3 O + (aq) + OH- (aq) 2 H 2 O (l) Oxidation-Reduction Reactions Metal + non-metal reaction The metal loses e - s & becomes a cation We call this process oxidation The nonmetal gains e - s & becomes an anion We call this process reduction In the reaction, e - s are transferred from the metal to the nonmetal 18

7 Oxidation-Reduction Reactions All reactions that involve a transfer of one or more e - s are called oxidationreduction reactions (REDOX) We say that the substance that loses electrons in the reaction is oxidized and the substance that gains electrons in the reaction is reduced. 7.5 Oxidation-Reduction Reactions metal + nonmetal ionic compound ionic cmpds always solids unless dissolved in water in the ionic cmpd the metal is the cation in the ionic cmpd the nonmetal is the anion to predict direct synthesis of metal + nonmetal determine the charges on the cation and anion from their position on the Periodic Table determine numbers of cations and anions needed to have charges cancel balance the equation Oxidation-Reduction Reactions Some reactions between two non-metals are also oxidation-reduction reaction Any reaction in which O 2 is a reactant or a product will be an oxidation-reduction reaction CH 4(g) + 2 O 2(g) CO 2(g) + 2 H 2 O (g) 2 SO 3(g) 2 SO 2(g) + O 2(g) The compound formed is not ionic 21

8 Ways to Classify Reactions Precipitation reactions: Acid-base reactions: Double displacement reactions: precipitation reactions acid-base reactions Will only occur if product is Insoluble Water 7.6 Ways to Classify Reactions Oxidation-reduction reactions: Metals + Nonmetal O 2 as a reactant or product Gas forming reactions: NaHCO 3(aq) + HCl (aq) NaCl (aq) + CO 2(g) + H 2 O (l) Ways to Classify Reactions Single replacement reaction: Zn (s) + 2 HCl (aq) ZnCl 2(aq) + H 2(g) Fe 2 O 3(s) + 2 Al (s) 2 Fe (s) + Al 2 O 3(s) 24

9 Other Ways to Classify Rxns Combustion Reactions O 2(g) is reacted with a C cmpd & release a lot of energy subclass of C cmpds produces H cmpds produces C 3 H 8(g) + 5 O 2(g) 3 CO 2(g) + 4 H 2 O (g) 7.7 Other Ways to Classify Rxns Synthesis Reactions Metal + Nonmetal rxns (also redox) 2 Na (s) + Cl 2(g) 2 NaCl (s) Rxns of Metals or Nonmetals with O 2 (also redox) N 2(g) + O 2(g) 2 NO (g) Other Ways to Classify Rxns Decomposition Reactions Generally initiated by addition of energy Addition of electric current or heat 2 H 2 O (l) electric 2 H 2(g) + O 2(g) current Opposite of a Synthesis Reaction 2 NaCl (l) electric 2 Na (l) + Cl 2(g) current 27

10 7.7 Other Ways to Classify Rxns 28