CHEM 139: Zumdahl Chapter 7 page 1 CHAPTER 7: REACTIONS IN AQUEOUS SOLUTIONS End-of-Chapter Problems: 1-84 7.5 REACTIONS OF METALS WITH NONMETALS COMBINATION/SYNTHESIS REACTIONS: A + Z ⎯→⎯Δ AZ – Two reactants combine to form one product when heated. – Given a metal and a nonmetal, recognize they react to form a solid ionic compound. Example: Predict the product for the following sets of reactants, then balance the equation. ____ Mg(s) + ____ O2(g) ⎯→⎯Δ ____ K(s) + ____ Br2(s) ⎯→⎯Δ ____ Al(s) + ____ S(s) ⎯→⎯Δ Note: The triangle above the reaction arrow ( ⎯→⎯Δ) indicates that the reactants are heated to make the reaction occur. COMBUSTION REACTIONS: CxHy + O2(g) ⎯→⎯Δ CO2(g) + H2O(g) (COMPLETE OXIDATION/BURNING) CxHyOz + O2(g) ⎯→⎯Δ CO2(g) + H2O(g) Hydrocarbons (compounds with only C and H) and hydrocarbon derivatives (compounds with only C, H and O) burn in O2 to produce CO2 gas and steam, H2O(g). Example: Predict the products for the following, then balance the equation. 1. ____ C3H8(g) + ____ O2(g) ⎯→⎯Δ 2. ____ C6H6O(l) + ____ O2(g) ⎯→⎯Δ 3. ____ C4H10(g) + ____ O2(g) ⎯→⎯ΔCHEM 139: Zumdahl Chapter 7 page 2 DECOMPOSITION REACTIONS: AZ → A + Z – One reactant breaks down into two or more products. – Given an unbalanced equation for a decomposition reaction, balance it and classify it. ____ KClO3(s) Δ, MnO2⎯ → ⎯ ⎯ ⎯ ____ KCl(s) + ____ O2(g) ____ Al2(CO3)3(s) ⎯→⎯Δ ____ Al2O3(s) + ____ CO2(g) ____ Fe(HCO3)3(s) ⎯→⎯Δ ____ Fe2O3(s) + ____ CO2(g) + ____ H2O(g) SINGLE-REPLACEMENT REACTIONS: A(s) + BX(aq) → AX(aq) + B ACTIVITY SERIES: Relative order of elements arranged by their ability to undergo reaction Li > K > Ba > Sr > Ca > Na > Mg > Al > Mn > Zn > Fe > Cd > Co > Ni > Sn > Pb > H2 > Cu > Ag > Au Note: The Activity Series will be given to you on quizzes and exams. SINGLE-REPLACEMENT REACTIONS: A SOLID METAL IN A METAL SOLUTION – The more active metal will go into solution=(aq). metal A(s) + aqueous solution B(aq) → aqueous solution A(aq) + metal B(s) Zn(s) + Sn2+(aq) → Sn(s) + Zn2+(aq) Cu(s) + 2 Ag+(aq) → 2 Ag(s) + Cu2+(aq)CHEM 139: Zumdahl Chapter 7 page 3 For each of the following, 1. Check the Activity Series to see if the solid metal is more active. – If it is, the reaction occurs, so write the formulas for the products – If it's not, write NR for "no reaction" 2. Balance the equation if the reaction occurs 1. _____ Zn(s) + _____ AgNO3(aq) → 2. _____ Al(s) + _____ ZnCl2(aq) → 3. _____ Ag(s) + _____ Al(NO3)3(aq) → SINGLE-REPLACEMENT REACTIONS: A METAL IN AN ACID For each of the following, 1. Check the Activity Series to see if the solid metal is more active than H. – If not, write NR for "no reaction" – If it is, the metal replaces hydrogen to form H2(g) and the metal goes into solution as a cation to join the anion. 2. Balance the equation if the reaction occurs. metal A(s) + acid(aq) → aqueous solution A(aq) + H2(g) 1. _____ Mg(s) + _____ HCl(aq) → 2. _____ Al(s) + _____ HBr(aq) → 3. _____ Cu(s) + _____ H2SO4(aq) →CHEM 139: Zumdahl Chapter 7 page 4 SINGLE-REPLACEMENT REACTIONS: ACTIVE METALS IN WATER ACTIVE METALS: Li > K > Ba > Sr > Ca > Na — Metals that react directly with water. For each of the following, 1. Check to see if the solid metal is an active metal. – If it's not, write NR for "no reaction". – If it is, the metal replaces hydrogen to form H2(g) and the metal goes into solution as a cation to combine with the hydroxide anion, OH−. 2. Balance the equation if the reaction occurs active metal(s) + H2O(l) → metal hydroxide(aq) + H2(g) 1. _____ Ca(s) + _____ H2O(l) → 2. _____ K(s) + _____ H2O(l) → 3. _____ Fe(s) + _____ H2O(l) → 7.2 REACTIONS IN WHICH A SOLID FORMS Some ionic compounds—usually those with ions with low charges like NaCl, KNO3, etc.—dissolve in water to form ions. See the examples of KNO3 and Pb(NO3)2 below:CHEM 139: Zumdahl Chapter 7 page 5 Other ionic compounds have stronger ionic bonds that cannotbe broken by polar H2O molecules. → These ionic compounds do not dissolve in water. → They are insoluble in water and remain intact as solids called “precipitates”. → For example, lead(II) iodide does not dissolves in water and remains a yellow solid (shown at the right). SOLUBILITY RULES: Indicate the ions in ionic compounds that are soluble or insoluble – The Solubility Rules will be given on quizzes and exams. soluble = compound dissolves in water → ions in solution → physical state is aqueous, (aq) insoluble = compound does not dissolve in water but remains a solid → physical state is shown as solid, (s) Solubility Rules for Ionic Compounds in Water Soluble if the ionic compound contains: 1. Li+, Na+, K+, NH4+ (ALWAYS!) 2. acetate ion (C2H3O2–), nitrate ion (NO3–), chlorate ion (ClO3–), perchlorate ion (ClO4–) 3. Halide ions (X–): Cl–, Br–, or I–, but AgX, Hg2X2, HgX, and PbX2 are insoluble 4. sulfate ion (SO42-), but CaSO4, SrSO4, BaSO4, Ag2SO4, PbSO4 are insoluble. Insoluble if the ionic compound contains: 5. carbonate ion, CO32- 6. chromate ion, CrO42- 7. phosphate ion, PO43- 8. sulfide ion (S2–), but CaS, SrS, and BaS are all soluble 9. hydroxide ion (OH–), but Ca(OH)2, Sr(OH)2, and Ba(OH)2 are all soluble Example: Use the Solubility Rules to determine the physical state when each ionic compound below is placed in water: a. CaCl2 b. Li2CrO4 c. PbBr2 d. K2CO3 e. Sr(OH)2 f. BaS g. Al(OH)3 h. Ag3PO4 i. Na2SCHEM 139: Zumdahl Chapter 7 page 6 PRECIPITATION REACTIONS Two solutions react to form a precipitate, an insoluble compound: AX(aq) + BZ(aq) → AZ(s) + BX(aq) precipitate The example at the right shows the following reaction: Fe(NO3)3(aq) + 3 NaOH(aq) → Fe(OH)3(s) + 3 NaNO3(aq) precipitate Guidelines for Predicting Products for Double-Displacement Precipitation Reactions 1. Exchange the anions, writing the formulas for the