Limiting Reagents, Solubility, and Solution Reactions

Limiting Reagents, Solubility, and Solution Reactions Key Questions & Exercises 1. See last week’s answer sheet. 2. See last week’s answer sheet. 3. See last week’s answer sheet. 4. NaCl is a strong electrolyte when dissolved in water, but pure solid NaCl does not conduct electricity. Why? The ions need to be able to move in order to conduct the current. The ions in an ionic solid can only vibrate (and sometimes rotate) about their fixed positions in the crystal lattice, so an ionic solid does not conduct electricity. 5. Which of the following terms might apply to an ionic solute: nonelectrolyte, strong electrolyte, weak electrolyte? Ionic solutes break up into their component ions when they dissolve in water. Therefore, all ionic solids are strong electrolytes. 6. Which of the following terms might apply to a molecular solute: nonelectrolyte, strong electrolyte, weak electrolyte? A molecular substance might be a nonelectrolyte (e.g., sugar, ethyl alcohol), a weak electrolyte (e.g., acetic acid, hypochlorous acid), or a strong electrolyte (e.g., hydrochloric acid). 7. Which kind(s) of solute particles (molecules, ions) exist in each of the following types of solutions? If more than one kind, which predominates? strong electrolyte - ions only weak electrolyte - molecules and some ions, with molecules predominating nonelectrolyte - molecules only 8. Categorize each of the following solutes as strong electrolyte, weak electrolyte, or nonelectrolyte: NaOH - strong CH3OH - nonelectrolyte AgC2H3O2 - strong HCO2H - weak NiSO4 - strong 9. Indicate whether the following ionic compounds are soluble or insoluble. Compound Solubility Compound Solubility PbCl2 insoluble Pb(CH3CO2)2 soluble KOH soluble Mg(OH)2 insoluble MgSO4 soluble BaSO4 insoluble CaCO3 insoluble (NH4)2CO3 soluble Hg2Cl2 insoluble CaCl2 soluble K2S soluble CuS insoluble 10. When two electrolyte solutions are mixed, new pairings of cations and anions may or may not result in a metathetical reaction. In order for a real reaction to take place, what possible products must a particular cation-anion pair produce? Metathesis occurs when a new cation-anion pairing would result in any of the following: (1) an insoluble compound (a precipitate), (2) neutralization (an acid-base reaction), or (3) a gas or other molecular species. 11. Write balanced ionic and net ionic equations for the reaction that occurs when each of the following pairs of solutions are mixed. If no precipitate forms, write “no reaction”. AgNO3(aq) + NaI(aq): Ag+(aq) + I–(aq) ÷ AgI(s) Pb(NO3)2(aq) + K2SO4(aq): Pb2+(aq) + SO42–(aq) ÷ PbSO4(s) Mg(NO3)2(aq) + K2SO4(aq): No reaction. (Magnesium sulfate is soluble) Ca(NO3)2(aq) + (NH4)3PO4(aq): 3 Ca2+(aq) + 2 PO43–(aq) ÷ Ca3(PO4)2(s) 12. Indicate whether each of the following is an acid or base, whether it is strong or weak, and show how you would write it (as molecules or ions) in an ionic equation. HCl and NH3 are given as examples. formula acid/base strong/weak written in solution as HCl acid strong H+(aq) + Cl–(aq) NH3 base weak NH3(aq) HCO2H acid weak HCO2H(aq) CH3NH2 base weak CH3NH2(aq) HClO4 acid strong H+(aq) + ClO4–(aq) HOCl acid weak HOCl(aq) 13. Write balanced net ionic equations for the following neutralizations. (Start by writing ionic equations, and then cancel any spectator ions.) Remember to write all weak electrolytes and molecular species in molecular form. KOH(aq) + HCO2H(aq): OH–(aq) + HCO2H(aq) ÷ H2O(l) + HCO2–(aq) HNO3(aq) + Ca(OH)2(aq): H+(aq) + OH–(aq) ÷ H2O(l) CH3NH2(aq) + HBr(aq): CH3NH2(aq) + H+(aq) ÷ CH3NH3+(aq) NaC2H3O2(aq) + HNO3(aq): C2H3O2–(aq) + H+(aq) ÷ HC2H3O2(aq) (acetate ion is also written CH3CO2–) 14. Write balanced net ionic equations for the following, remembering to write all solids, liquids, weak electrolytes, or molecular species in molecular form. (Start by writing ionic equations, and then cancel any spectator ions.) NH4Cl(aq) + Ca(OH)2(aq): NH4+(aq) + OH–(aq) ÷ NH3(g) + H2O(l) PbS(s) + HNO3(aq): PbS(s) + 2 H+(aq) ÷ H2S(g) + Pb2+(aq) NaHCO3(aq) + CH3CO2H(aq): HCO3–(aq) + CH3CO2H(aq) ÷ H2O(l) + CO2(g) + CH3CO2–(aq) CaCO3(s) + HCl(aq): CaCO3(s) + 2 H+(aq) ÷ H2O(l) + CO2(g) + Ca2+(aq)