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Chapter 4 Aqueous Reactions and Solution Stoichiometry Chemistry, The Central Science, 10th edition Theodore L. Brown; H. Eugene LeMay, Jr.; and Bruce.

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Presentation on theme: "Chapter 4 Aqueous Reactions and Solution Stoichiometry Chemistry, The Central Science, 10th edition Theodore L. Brown; H. Eugene LeMay, Jr.; and Bruce."— Presentation transcript:

1 Chapter 4 Aqueous Reactions and Solution Stoichiometry Chemistry, The Central Science, 10th edition Theodore L. Brown; H. Eugene LeMay, Jr.; and Bruce E. Bursten

2 4.1 Properties of Aqueous Solutions

3 Solutions (abrev. sol’n) Homogeneous mixtures of two or more pure substances –can be liquids or gases. Solvent - substance present in the greatest quantity Solute(s) - All other substances present in lesser quantities Solutions in which water is the solvent are called aqueous solutions

4 Water – a great solvent! H 2 O molecules can attract, separate, and surround the cations and anions that make up many ionic compounds –Solvation - the process of a solvent surrounding and dissolving an ionic compound  the cations & anions become dissociated (or separated) as they are surrounded by the H 2 O molecules The dissociated ions are free to move and become evenly dispersed throughout the solution. –the moving ions can carry a current throughout the solution resulting in electrical conductivity (movement of charged particles through a medium).

5 NaCl + H 2 O

6 Ionic Compounds in Water While water is an excellent solvent, not ALL ionic substances will readily dissolve and dissociate in the presence of H 2 O Those that DO dissociate are known as electrolytes: –Electrolyte - a substance which contains ions and conducts electricity in it’s aqueous form –There are 3 classifications of electrolytes: strong, weak, and nonelectrolytes

7 Strong Electrolytes dissociates completely into ions when dissolved in H 2 O sol’n exists as 100% ions (no bonded ionic compounds left undissolved) good conductor of electricity Includes: –all soluble * ionic compounds –all strong acids & bases* –a few covalent compounds * explained on a later slide

8 Weak Electrolytes dissociate only partially into ions when dissolved in H 2 O sol’n exists mostly as molecules surrounded by water (very, very few ions present) poorly conducts electricity Includes: –weak acids & bases* (ex: acetic acid, HC 2 H 3 O 2 [only 1% as ions]) –slightly soluble ionic compounds* –some covalent compounds

9 Nonelectrolytes do NOT dissociate into ANY ions dissolved substance consists of intact molecules surrounded by H 2 O does not conduct electricity Includes: –most covalent compounds (w/the exception of acids & bases which are either strong or weak)

10 Electrolytes: a visual

11 Solubility – ability to be dissolved Soluble (aq) –a substance which easily dissolves in water Slightly Soluble (s) –a substance that only dissolves a tiny bit in water Insoluble (s) –substance that does NOT dissolve in water –substance remains separate from the H 2 O molecules (no interaction) –substances are insoluble when the ions attract so strongly that they CANNOT be pulled apart by H 2 O molecules

12 Solubility: a visual

13 Solubility Rules To know if an ionic substance is soluble or not, you must consult the solubility rules –lists which ions are typically soluble and insoluble –also lists exceptions to the rules Note: Acids are not explicitly listed in the rules because all acids are aqueous solutions (thus soluble)

14 Solubility Rules for Common Ionic Compounds in Water Soluble Ionic CompoundsExceptions: these are insoluble w/ respective anions Nitrates, NO 3 - none Acetates, C 2 H 3 O 2 - none Chlorides, Cl - Ag +, Hg 2 2+ (2 Hg atoms), Pb 2+ Bromides, Br - Ag +, Hg 2 2+, Pb 2+ Iodides, I - Ag +, Hg 2 2+, Pb 2+ Sulfates, SO 4 2- Ag +, Hg 2 2+, Pb 2+, Sr 2+, Ba 2+ Alkali metal cationsnone Ammonium, NH 4 + none Insoluble Ionic CompoundsExceptions: these are soluble w/ respective anions Sulfides, S 2- alkali metal cations, NH 4 +, Ca 2+, Sr 2+, Ba 2+ Carbonates, CO 3 2- alkali metal cations, NH 4 + Phosphates, PO 4 3- alkali metal cations, NH 4 + Hydroxides, OH - alkali metal cations, NH 4 +, Ca 2+, Sr 2+, Ba 2+

15 Solubility Rules - Practice Are the following soluble or insoluble? – Be(C 2 H 3 O 2 ) 2 – MgS – BaSO 4 – K 3 PO 4 soluble insoluble

16 Acids Substances that produce H + ions when dissolved in water (Arrhenius). Ex) HNO 3  H + + NO 3 – Substances that produce OH − ions when dissolved in water (Arrhenius). Ex) NaOH  Na + + OH – Bases

17 Strong vs. Weak Both strong & weak acids and bases exist –Strong acids & bases dissociate completely in solution Exist as 100% ions Strong electrolytes & conductors –Weak acids & bases only partially dissociate in solution Few ions exits Weak electrolytes & conductors

18 Strong vs. Weak Electrolytes Strong Acid: Weak Acid: HCl HNO 2

19 Seven Strong Acids MUST BE MEMORIZED! Hydrochloric (HCl) Hydrobromic (HBr) Hydroiodic (HI) Nitric (HNO 3 ) Sulfuric (H 2 SO 4 ) Chloric (HClO 3 ) Perchloric (HClO 4 ) **When dissolved in water, they dissociate 100% into H + ions and their respective anion.**

20 Strong Bases MUST BE MEMORIZED!  Soluble hydroxide compounds Alkali metal hydroxides LiOH, NaOH, KOH, etc… Calcium hydroxide, Ca(OH) 2 Strontium hydroxide, Sr(OH) 2 Barium hydroxide, Ba(OH) 2 When dissolved in water, they dissociate 100% into their respective metal cation and OH –

21 Predicting Ions in Solution If a substance is soluble, you can predict what ions present are in the solution –Ex) Ammonium sulfate (NH 4 ) 2 SO 4  soluble Dissociates into: 2 NH 4 + ions 1 SO 4 2- ion –Ex) Sulfuric Acid H 2 SO 4  soluble Dissociates into: 2 H + ions 1 SO 4 2- ion

22 How to Classify Electrolytes Ask… Is the substance ionic, covalent, or an acid/base? If ionic, is it soluble? –If soluble = strong electrolyte –If insoluble = nonelectrolyte If covalent –If covalent and NOT an acid or base = generally nonelectrolyte (ex: sugar, organic compounds) If acid or a base, is it a strong acid/base? –If strong acid or base = strong electrolyte –if it is any other acid or base = weak electrolyte

23 Classify the following as: strong, weak, or nonelectrolyte 1)CaCl 2 2)HNO 3 3)Ag 3 PO 4 4)HCHO 2 5)KOH 6)C 2 H 5 OH – ionic – soluble = Strong – acid = Strong – ionic – insoluble = Nonelectrolyte – acid = Weak – ionic – soluble = Strong (also strong base) – covalent– NOT a base = Nonelectrolyte

24 Classify the following as: strong, weak, or nonelectrolyte 1) Mg(OH) 2 2) HCl 3) H 3 PO 4 4) (NH 4 ) 2 CO 3 5) H 2 SO 4 – ionic – insoluble = nonelectrolyte – strong acid = strong – weak acid = weak – ionic – soluble = strong – strong acid = strong

25 4.2 Precipitation Rxns

26 Precipitation Rxns Double replacement reactions that specifically produce a solid product –This solid product is called a precipitate (abbreviated ppt.) and is known as insoluble (because it cannot readily dissolve in water) To predict if an insoluble ppt will form, use the solubility rules

27 Predicting Precipitations Rxns 1.Predict the products of the double replacement reaction (cations switch partners) 2.Use solubility rules to determine the states of matter of the products:  insoluble = (s); soluble = (aq)  If a solid is formed, a ppt rxn has occurred

28 1. Fe(NO 3 ) 3 (aq) + K 2 S (aq) 2 Fe(NO 3 ) 3 (aq) + 3 K 2 S (aq)  Fe 2 S 3 (s) + 6 KNO 3 (aq) 2. Li 2 CO 3 (aq) + KC 2 H 3 O 2 (aq) Li 2 CO 3 (aq) + KC 2 H 3 O 2 (aq)  2 LiC 2 H 3 O 2 (aq) + K 2 CO 3 (aq)  NR (no reaction) = a bunch of ions in a puddle Predicting Precipitation Rxns Practice

29 DEMO!!! Will precipitates form? Solutions Used:  0.1 M KI  0.1 M Pb(NO 3 ) 2  0.1 M CaCl 2

30 Balanced Chemical Equations Balanced chemical equations show chemical formulas without considering the ionic character of any substances However… recall that soluble ionic compounds are strong electrolytes  strong acids, strong bases, and soluble ionic salts This means they dissociate and are truly present as ions in a sol’n (which leads us to…)

31 …Ionic Equations Complete Ionic (CIE): explicitly indicates all the IONS that are in sol’n throughout the rxn  Spectator Ions = ions present on BOTH sides of the chemical equation Ions are present but play NO DIRECT ROLE in chemical rxn When ALL reactants and products are AQUEOUS (no reaction), every ion is a spectator ion (so CIE is not usually written)

32 …Ionic Equations Net Ionic (NIE):  includes only ions and compounds directly involved in the chemical rxn  This means NO spectators are included

33 CIE & NIE Practice Mg(NO 3 ) 2 (aq) + Li 2 SO 4 (aq) Balanced Equation: Mg(NO 3 ) 2 (aq) + Li 2 SO 4 (aq)  MgSO 4 (aq) + 2 LiNO 3 (aq) = NR Complete Ionic Equation: Mg 2+ (aq) + 2 NO 3 - (aq) + 2 Li + (aq) + SO 4 2- (aq)  Mg 2+ (aq) + SO 4 2- (aq) + 2 Li + (aq) + 2 NO 3 - (aq) Net Ionic Equation: NONE! – all spectators

34 6 NH 4 + (aq) + 2 PO 4 3- (aq) + 3 Ba 2+ (aq) + 3 S 2- (aq)  6 NH 4 + (aq) + 3 S 2- (aq) + Ba 3 (PO 4 ) 2 (s) (NH 4 ) 3 PO 4 (aq) + BaS (aq) Balanced Equation: 2 (NH 4 ) 3 PO 4 (aq) + 3 BaS (aq)  3 (NH 4 ) 2 S (aq) + Ba 3 (PO 4 ) 2 (s) Complete Ionic Equation: Net Ionic Equation: 2 PO 4 3- (aq) + 3 Ba 2+ (aq)  Ba 3 (PO 4 ) 2 (s) … NO spectators! CIE & NIE Practice

35 4.4 Oxidation- Reduction Reactions

36 Single Replacement Rxns General Rxn Formula: A + BC  AC + B The reactants: –One reactant is a single element by itself –The other reactant is an ionic compound The products: –If the single element is a metal, it will replace the cation in the ionic compound –If the single element is a halogen gas, it will replace the anion in the ionic compound

37 Oxidation-Reduction Rxns (aka: Redox) All single replacement rxns can be classified as Redox rxns (but not all redox rxns are single replacement) Redox rxns occur when electrons are transferred between reactants Oxidation occurs when an atom, ion, or molecule loses electrons. (LEO) Reduction occurs when an atom, ion, or molecule gains electrons. (GER) * Both processes happen simultaneously in a rxn

38 Activity Series of Metals - Ease of Oxidation When a single replacement rxn occurs, the metal that is alone will be oxidized. However, some metals are easier to oxidize than others (they lose electrons more easily than others, thus forming cations) –Active Metals: metals at the top of the activity series are more reactive and more easily oxidized –Noble Metals: metals at the bottom of the activity series which have very low reactivity

39 In a single replacement rxn: (1)a solid metal element can be OXIDIZED by any elements listed below it in the activity series (2)Look to see if the metal solid is ABOVE the metal cation (in the 2 nd reactant)  If yes, the rxn does happen  predict products  If not, NR (b/c the solid metal cannot be oxidized) Activity Series of Metals

40 Using the Activity Series Examples 1) magnesium sulfate+ zinc metal 2) iron metal + copper (II) nitrate  NR Fe (s) + Cu(NO 3 ) 2 (aq)  Cu (s) + Fe(NO 3 ) 2 CIE: Fe (s) + Cu 2+ (aq) + 2 NO 3 – (aq)  Cu (s) + Fe 2+ (aq) + 2 NO 3 – (aq) We can also write CIE & NIE!!! (only aqueous dissociate) NIE: Fe (s) + Cu 2+ (aq)  Cu (s) + Fe 2+ (aq)

41 Metals Reacting w/Acids Only metals listed ABOVE hydrogen in the series are able to react with acids If the reaction does occur, H 2 gas is produced. Example #1: ___Ni (s) + ___HCl (aq)   Ni is above H 2, so the rxn occurs! Example #2: ___Cu (s) + ___HCl (aq)   Cu is below H 2, so no rxn occurs! NiCl 2 (aq) + H 2 (g) NR 2

42 Activity Series of Halogens: The idea is the same here… –Fluorine is the most reactive –Iodine is the least reactive Only a MORE reactive halogen can replace a LESS reactive one In these single replacement rxns, the single element (halogen gas) must be listed ABOVE the halogen anion in the 2 nd reactant for a rxn to occur ___Cl 2 + ___NaBr (aq)  ___NaCl (aq) + ___Br 2 (g) 2 A CTIVITY S ERIES OF H ALOGENS : Fluorine Chlorine Bromine Iodine 2


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