Reactions in Aqueous Solution

Properties of Aqueous Solutions Chapter 4  Reactions in Aqueous Solution    1 Electrolytes in Aqueous Solutions Substances behave differently when they are placed in water, specifically ionic versus covalent compounds. One breaks apart in water, the other does not. Which one is more likely to be pulled apart by water molecules? Electrolytes are ionic and strong acid solutions (e.g., GatoradeTM); Nonelectrolytes are covalent compounds (e.g., sugar); weak electrolytes are in between. Electrolytic Properties  Strong/Weak Electrolytes   Electrolytes in Aqueous Solutions Strong electrolyte: substance that, when dissolved in water, results in a solution that can conduct electricity (NaCl) soluble ionic compounds, strong acids Weak electrolyte: substance that is a poor conductor of electricity when dissolved in water (CH3COOH – vinegar) insoluble ionic compounds, weak acids Nonelectrolyte: substance that doesn’t conduct electricity when dissolved in water (CH3OH – methanol), covalent compounds Properties of Aqueous Solutions   Most reactions in general chemistry take place in an aqueous environment. What does that mean? Terms:  Solution: homogeneous mixture of two or more substances  Solute: substance present in smaller amount  Solvent: substance present in greater amount  Aqueous solution: solvent is water Strong/Weak Electrolytes 1 Ways Reactions Occur  Precipitation (Double-Replacement) Reactions  Three general categories:  Precipitation: insoluble (solid) product is formed  from aqueous solutions  Acid-base neutralization: acid and base react to  form water and a salt (ionic compound)  Oxidation-Reduction: electrons are transferred between atoms in reaction    Combination Decomposition Single-replacement (metal or hydrogen)  Solubility Rules – on periodic table        Solubility Rules Answers         Determine if the following ionic compounds will be soluble (aq) or insoluble (s) in water: K2CO3 soluble (aq) BaSO4 insoluble (s) PbI2 insoluble (s) NaClO4 soluble (aq) Ag2S insoluble (s) (NH4)3PO4 soluble (aq) Cu(OH)2 insoluble (s) Write formulas of products (based on charges), predict phases (Solubility Rules on back of periodic table), and balance the equation. Solubility Rules  If not covered by the rules, it is probably insoluble. Precipitation reactions always begin with two ionic compounds. Example: NaCl (aq) + AgNO3 (aq)  ? Draw these compounds in two separate aqueous environments. What are the possible products when they are combined? Determine if the following ionic compounds will be soluble (aq) or insoluble (s) in water: K2CO3 BaSO4 PbI2 NaClO4 Ag2S (NH4)3PO4 Cu(OH)2 10 Molecular, Ionic, and Net Ionic Equations  There are 3 ways to represent ppt reactions:  As whole compounds (molecular equation)  As ionic species (ionic equation) – more accurate  As participants in reaction (net ionic equation)   Any aqueous ionic substance is written as a compound (e.g., AgNO3), but this isn’t accurate. What does this look like in water? It is Ag+ and NO3- ions Solids, liquids, and gases remain as compounds. 13 2 Formation of Silver Chloride  Molecular equation: Chemistry humor, ha ha!  NaCl(aq) + AgNO3(aq)  AgCl(s) + NaNO3(aq)  Ionic equation (write separate ions for soluble (aq) compounds):  Na+(aq) + Cl-(aq) + Ag+(aq) +NO3-(aq)  AgCl(s) + Na+(aq) + NO3-(aq)     Net ionic equation (cancel any identical ion on both sides of the equation, called spectator ions): Ag+(aq) + Cl-(aq)  AgCl(s)  Note: s, l, and g stay together!!!!! Ag+/Cl- ions Precipitation Reactions Acid-Base (Double-Replacement) Reactions Reaction of lead (II) nitrate and potassium iodide. What is the precipitate? Write the molecular, ionic, and net ionic equations. Worked Ex. 4.2 – 4.5; Problems 4.4 – 4.8  Acid: substance that breaks apart in water to form H+ (e.g., HCl, HNO3, CH3COOH, lemon, lime, vitamin C).  Base: substance that breaks apart in water to form OH- (e.g., NH3, DranoTM, Milk of MagnesiaTM)  HA(aq)  H+(aq) + A-(aq)  MOH(aq)  M+(aq) + OH-(aq) acid strong acid base weak acid 17 Common Acids and Bases  Acid-Base Neutralization You need to KNOW these!!!       Strong acids: HCl, HBr, HI, HClO4, H2SO4, HNO3 Strong bases: LiOH, KOH, NaOH, RbOH, CsOH, Ca(OH)2, Sr(OH)2, Ba(OH)2 Neutralization reaction: reaction between acid and base; products are usually a salt (ionic compound) and water HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l) Acid + base  salt + water What are the ionic and net ionic equations for these reactions?  KOH (aq) + H2SO4 (aq)   NH3 (aq) + HCl (aq)   Worked Ex. 4.6, 7; Problems 4.9, 4.10, 11 18 3 Acid-Base Reaction Group Work  Determine the products of the reaction. Identify the phase of each compound, and balance the equation. Also write the ionic and net ionic equations. Molecular: Na2S + Cr(NO3)3   Complete Ionic:  Net Ionic:  HCl Acid + Base → H2O + Salt Mg(OH)2 Water is created from H+ and OH- 2HCl(aq) + Mg(OH)2(s) → 2H2O(l) + MgCl2(aq) The salt is created from spectator ions Complete/Balance These Equations Group Answers  Molecular: 3Na2S(aq) + 2Cr(NO3)3(aq)  Cr2S3(s) + 6NaNO3(aq)  Complete Ionic: 6Na+(aq) + 3S2-(aq) + 2Cr3+(aq) + 6NO3-(aq)  Cr2S3(s) + 6Na+(aq) + 6NO3-(aq)   Complete and balance these equations. Write ionic and net ionic equations, if applicable. Na2S(aq) + CuCl2(aq)   KNO3(aq) + CaCl2(aq)   KOH(aq) + H2SO4(aq)   Net Ionic: 2Cr3+(aq) + 3S2-(aq)  Cr2S3(s) 23 Complete/Balance These Equations  Oxidation-Reduction Reactions Na2S(aq) + CuCl2(aq)  2 NaCl(aq) + CuS(s)  Oxidation-Reduction (redox) reactions: electron-transfer reactions  When iron rusts, it loses electrons to form a cation, oxygen gain electrons to form an anion: 4 Fe(s) + 3 O2(g) 2 Fe2O3(s) Use oxidation number rules to determine gain and loss of electrons. Oxidation numbers are assigned as if elements in compounds completely transferred electrons (like in ionic compounds).  Cu2+(aq) + S2-(aq)  CuS(s)  2 KNO3(aq) + CaCl2(aq)  2 KCl(aq) + Ca(NO3)2(aq)  No reaction   2KOH(aq) + H2SO4(aq)  2H2O (l) + K2SO4 (aq)   H+ (aq) + OH- (aq)  H2O (l) 24 4 Assigning Oxidation Numbers     Rules continued  1) An atom (or molecule) in its elemental state has an oxidation number of 0. 2) An atom in a monatomic ion (Na+, Cl-) has an oxidation number identical to its charge. 3a) Hydrogen has an oxidation number of +1, unless it is combined with a metal, in which case it has an oxidation number of –1. 3b) Oxygen usually has an oxidation number of -2. Oxygen in peroxides (O22-) has an oxidation number of -1.  3c) Halogens usually have an oxidation number of -1 (except when bonded to oxygen or in polyatomic ions). 4) The sum of oxidation numbers is 0 for a neutral compound and is equal to the net charge for a polyatomic ion. (Example: NaCl = 0, SO42- = -2)  4a) For binary ionic compounds, the position of the element in the periodic table may be useful:  Group IA: +1; Group IIA: +2; Group VIIA: –1; Group VIA: –2; Group VA: –3 26 Example  Assigning Oxidation Numbers H2SO4   27  H = +1; O = –2 S is unknown, so leave this for last.  The overall charge on this compound is 0.  Use algebra to solve for S:  2(+1) + 1(x) + 4(-2) = 0   Solve for each element: MgCr2O7 Worked Ex. 4.8; Problem 4.13 Determine values of the oxidation number of each element in these compounds or ions: H2O SO2 CCl4 H2O2 Fe3(PO4)2 MnO4NaNO3 KClO4 28 Assigning Oxidation Numbers  29 Oxidation-Reduction Reactions Determine values of the oxidation number of each element in these compounds or ions: H2O H: +1, O: -2 SO2 S: +4, O: -2 CCl4 C: +4, Cl: -1 H2O2 H: +1, O: -1 Fe3(PO4)2 Fe: +2, P: +5, O: -2 MnO4- Mn: +7, O: -2 NaNO3 Na:+1, N:+5, O: -2 KClO4 K: +1, Cl: +7, O: -2    Oxidized: atom, molecule, or ion becomes more positively charged  Loss of electrons is oxidation (LEO) Reduced: atom, molecule, or ion becomes less positively charged (reduced charge)  Gain of electrons is reduction (GER) Or: OIL RIG (oxidation is loss; reduction is gain) Redox 1 Redox 2 30 5 Assigning Oxidation Numbers Oxidation-Reduction Reactions     Oxidation-Reduction Reactions   Identify the element or ion oxidized/reduced. Also identify the oxidizing agent and the reducing agent. Zn(s) + 2HCl(aq)  ZnCl2(aq) + H2(g) Group Work     Reduced Oxidized      Ba: +2 Cl: +5 O: -2  Identify the oxidation number of each element in the compounds or ions below: Ba(ClO3)2 SO32For the reaction below, identify what has been oxidized and reduced; identify the oxidizing agent and the reducing agent. Cu(s) + 2AgNO3(aq)  2Ag(s) + Cu(NO3)2(aq) Redox Reactions Group Answers  The substance oxidized causes the other substance to be reduced and is called the reducing agent. The substance reduced causes the other substance to be oxidized and is called the oxidizing agent. 4 Fe(s) + 3O2(g)  2Fe2O3(s) Worked Ex. 4.9; Problems 4.14, 4.15 S: +4 O: -2 Cu(s) + 2AgNO3(aq)  2Ag(s) + Cu(NO3)2(aq) Cu: oxidized Ag+: reduced Cu: reducing agent AgNO3: oxidizing agent  Combination (1 product)  Decomposition (1 reactant) – usually give off gases  Single Replacement (or Displacement) (start and end with an element and a compound)  Na(s) + Cl2(g)   CuCO3(s)   Zn(s) + HCl(aq)  37 6 Combination Reactions  element + element  metal + nonmetal  nonmetal + nonmetal compound  Why are these redox reactions? Combination Reactions  compound Mg + O2 K + Cl2  H2(g) + O2(g)  ionic compound  Na(s) + Cl2(g)  covalent C(s) + O2(g) 38 Decomposition Rxns Produce Gases   Decomposition Reactions  Compound 2 elements; element + compound; or 2 compounds Oxides, peroxides   NH4Cl (s) NiCO3(s) CuO(s)  Give off O2  Nitrates  Give off NO2 , NO2-  Carbonates  Ammonium salts  Give off CO2  Give off NH3 40 Single-Displacement Reactions  element + compound compound + element (The more metallic/active element in the compound is displaced.)  Metal Displacement Single Displacement: Cu + AgNO3  Zn(s) + Cu(NO3)2(aq)  Cu(s) + Zn(NO3)2(aq)  Hydrogen Displacement  Mg(s) + HCl(aq) MgCl2(aq) + H2(g) Alkali Metals Zn+SnCl2 42 43 7 Single Displacement: Fe + Cu(NO3)2 Activity Series The higher the metal on the activity series, the more active that metal. Translation: higher metals on the chart will form ions as products.   45 Predict whether a reaction occurs        Na + H2O Fe + H2O Fe + Cr(NO3)2 Ni + Pb2+ Ag + Mg2+ Zn + Co2+ Worked Ex. 4.10; Problems 4.16, 4.17 Combustion Reactions  React w/ cold water  React w/ steam   Burning hydrocarbons CxHyOz + O2 (g)  CO2 (g) + H2O (g) Methanol, CH3OH _CH3OH (l) + _O2 (g)  _CO2 (g) + _H2O (g) React w/ acid 46 Reaction Types Types of Reactions Summary       Reaction Types Animated Precipitation: use Solubility Rules (AB + CD  AD + CB) Acid-Base Neutralization: acid + base  salt + water (AB + CD  AD + H2O) Combination: start with elements (A + B  AB) Decomposition: often produces gas (AB  A + B) Single Displacement: use Activity Series to predict if a reaction occurs (A + BC  B + AC) Combustion: Classify (and balance) these rxns 1. Co(s) + AgNO3(aq)  2. Fe(s) + HCl(aq)  3. Na2CO3(s) 4. Ca(s) + H2O(l)  5. CaCO3(s) 6. HClO4(aq) + KOH (aq)  7. BaCl2(aq) + Na2SO4(aq)   Hydrocarbon + O2(g)  CO2(g) + H2O(g) 49 8 Classify (and balance) these rxns 8. HgO(s) 9. LiOH(aq) + H2SO4(aq)  10. Na2CrO4(aq) + Ni(NO3)2(aq)  11. Li(s) + O2(g)  12. Mg(OH)2(aq) + 2HCl(aq)  13. NH3(g) + HCl(g)  14. NiCO3(s) 15. Ca(s) + F2(g)  Group Work       Determine what type of reaction will happen for each set of reagents below. Predict products of the following reactions. Write correct phases for the products and balance each equation: ___ Al (s) + ___ NaNO3 (aq)  ___ Na (s) + ___ O2 (g)  ___ Na2SO4 (aq) + ___ Pb(NO3)2 (aq)  Classify these reactions by type Single disp. 1. Co(s) + 2AgNO3(aq)  Co(NO3)2(aq) + 2Ag(s) Single disp. 2. Fe(s) + 2HCl(aq)  FeCl2(aq) + H2(g) Decomp. 3. Na2CO3(s)  Na2O(s) + CO2(g) Single disp. 4. Ca(s) + 2H2O(l)  Ca(OH)2(aq) + H2(g) Decomp. 5. CaCO3(s) + heat  CaO (s) + CO2(g) Acid-base neut. 6. HClO4(aq) + KOH(aq)  KClO4(aq) + H2O(l) Precip. 7. BaCl2(aq) + Na2SO4(aq)  BaSO4(s) + 2NaCl(aq) Decomp. 8. 2HgO(s)  2Hg(l) + O2(g) Acid-base neut. 9. 2LiOH(aq) + H2SO4(aq)  Li2SO4(aq) + 2H2O(l) Precip. 10. Na2CrO4(aq) + Ni(NO3)2(aq)  2NaNO3(aq) + NiCrO4(s) Combo. 11. 4Li(s) + O2(g)  2Li2O(s) Acid-base neut. 12. Mg(OH)2(aq) + 2HCl(aq)  2MgCl2(aq) + H2O(l) Combo. 13. NH3(g) + HCl(g)  NH4Cl(s) Decomp. 14. NiCO3(s)  NiO(s) + CO2(g) Combo. 15. Ca(s) + F2(g)  CaF2(g) Group Answers  SR: Al (s) + NaNO3 (aq)  No reaction  Combo: 4 Na (s) + O2 (g)  2 Na2O (s)  DR/PPT: Na2SO4 (aq) + Pb(NO3)2 (aq)  2NaNO3 (aq) + PbSO4 (s) The End  Given reactants, be able to identify the reaction type, predict the products of reaction (with correct phases), and balance the equation – similar to the worksheet questions! 9