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AP Chem Problem Set # 2













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Balancing Chemical Equations

1. Balance the following equations:

    1. CO(g) + O2(g) CO2(g)

    2. N2O5(g) + H2O(l) HNO3(ag)

    3. PCl5(l) + H2O(l) H3PO4(aq) + HCl(aq)

    4. CH4(g) + Br2(g) CBr4(l) + HBr(g)

    5. C5H10O2(l) + O2(g) CO2(g) + H2O(l)

    6. Cr(OH)3(s) + HclO4(aq) Cr(ClO4)3(aq) + H2O(l)

    7. (NH4)2Cr2O7(aq) Cr2O3(s) + N2(g) + H2O(l)

2. Write balanced chemical equations to correspond to each of the following descriptions: (a) Solid calcium carbide, CaC2; reacts with water to form an aqueous solution of calcium hydroxide and acetylene gas, C2H2. (b) When solid potassium chlorate is heated, it decomposes to form solid potassium chloride and oxygen gas. (c) Solid zinc metal reacts with sulfuric acid to form hydrogen gas and an aqueous solution of zinc sulfate. (d) When liquid phosphorus trichloride is added to water, it reacts to form aqueous phosphorous acid, H3PO3(aq), and aqueous hydrochloric acid. (e) When hydrogen sulfide gas is passed over solid hot iron(III) hydroxide, the resultant reaction produces solid iron(III) sulfide and gaseous water.

Patterns of Chemical Reactivity

3. (a) What products form when a hydrocarbon is completely combusted in air? Write a balanced chemical equation for the combustion of octane, C8H18(l), in air. (b) How can you determine the chemical formula of the product formed when the metallic element calcium combines with the nonmetallic element oxygen, O2? Write the balanced chemical equation for the reaction.

4. Write a balanced chemical equation for the reaction that occurs when (a) the hydrocarbon heptane, C7H16(l), is combusted in air; (b) the gasoline additive MTBE (methyl tertiary-butyl ether), C5H12O(l), burns in air; (c) Rb(s) reacts with water; (d) Mg(s) reacts with Cl2(g).

5. Balance the following equations, and indicate whether they are combustion, combination, or decomposition reactions:

  1. Al(s) + Cl2(g) AlCl2(s)

  2. C2H4(g) + O2(g) CO2(g) + H2O(l)

  3. Li(s) + N2(g) Li3N(s)

  4. PbCO3(s) PbO(s) + CO2(g)

  5. C7H8O2(l) + O2(g) CO2(g) + H2O(l)

    Additional Exercises

    6. Write the balanced chemical equation for (a) the complete combustion of butyric acid, C4H8O2(l), a compound produced when butter becomes rancid; (b) the decomposition of solid copper(II) hydroxide into solid copper(II) oxide and water vapor; (c) the combination reaction between zinc metal and chlorine gas.

    Electrolytes

    7. Although pure water is a poor conductor of electricity, we are cautioned not to operate electrical appliances around water. why?

    8. When methyl alcohol, CH3OH, is dissolved in water, a non-conducting solution results. When acetic acid, HC2H3O2, dissolves in water, the solution is weakly conducting and acidic in nature. Describe what happens upon dissolution in the two cases, and account for the different results.

    9. Specify how each of the following strong electrolytes ionizes or dissociates into ions upon dissolving in water: (a) ZnCl2; (b) HNO3; (c) FeSO4; (d) (NH4)2CO3.

    10. Formic acid, HCHO2, is a weak electrolyte. What solute particles are present in an aqueous solution of this compound? Write the chemical equation for the ionization of HCHO2.

    Precipitation Reactions and Net Ionic Equations

    11. Using solubility guidelines, predict whether each of the following compounds is soluble or insoluble in water: (a) NiCl2; (b) Ag2S; (c) Cs3PO4; (d) SrCO3; (e) (NH4)2SO4.

    12. Will precipitation occur when the following solutions are mixed? If so, write a balanced chemical equation for the reaction. (a) Na2CO3 and AgNO3; (b) NaOH and K2SO4; (c) FeSO4 and Pb(NO3)2.

    13. Write the balanced complete ionic equations and net ionic equations for the reactions that occur when each of the following solutions are mixed.

    (a) Na2CO3(aq) and MgSO4(aq)

  6. Pb(NO3)2(aq) and Na2S(aq)

  7. (NH4)3PO4(aq) and CaCl2(aq)

14. Separate samples of a solution of an unknown ionic compound are treated with dilute AgNO3, Pb(NO3)2, and BaCl2. Precipitates form in all three cases. Which of the following anions could be the anion of the unknown salt: Br-; CO32-; NO3-?

Acid-Base Reactions

15. What is the difference between: (a) a monoprotic acid and a diprotic acid; (b) a weak acid and a strong acid; (c) an acid and a base?

16. Classify each of the following as a strong or weak acid or base: (a) HClO4; (b) HClO2; (c) LiOH; (d) NH3.

17. An aqueous solution of an unknown solute is tested with litmus paper and found to be acidic. The solution is weakly conducting compared with a solution of NaCl of the same concentration. Which of the following substances could the unknown be: KOH, NH3, HNO3, KClO2, H3PO3, CH3COCH3 ?

18. Classify each of the following substances as a non-electrolyte, weak electrolyte, or strong electrolyte in water: (a) H2SO3; (b) ethanol, C2H5OH; (c) NH3; (d) KClO3; (e) Cu(NO3)2.

19. Complete and balance the following molecular equations, and then write the net ionic equation for each:

  1. HBr(aq) + Ca(OH)2(aq)

  2. Cu(OH)2(s) + HClO4(aq)

  3. Cr(OH)3(s) + HNO3(aq)

20. Write balanced molecular and net ionic equations for the following reactions, and identify the gas formed in each: (a) solid cadmium sulfide reacts with an aqueous solution of sulfuric acid; (b) solid magnesium carbonate reacts with an aqueous solution of perchloric acid.

Oxidation-Reduction Reactions

21. Where, in general, do the most easily oxidized metals occur in the periodic table? Where do the least easily oxidized metals occur in the periodic table?

22. Determine the oxidation number for the indicated element in each of the following substances: (a) S in SO3; (b) C in COCl2; (c) Mn in MnO4-; (d) Br in HbrO; (e) As in As4; (f) O in K2O2.

23. Which element is oxidized, and which is reduced in the following reactions?

  1. Ni(s) + Cl2(g) NiCl2(s)

  2. 3Fe(NO3)2(aq) + 2Al(s) 3FE(s) + 2Al(NO3)3(aq)

  3. Cl2(aq) + 2NaI(aq) I2(aq) + 2NaCl(aq)

  4. PbS(s) + 4H2O(aq) PbSO4(s) + 4H2O(l)

24. Write balanced molecular and net ionic equations for the reactions of (a) hydrochloric acid with nickel; (b) sulfuric acid with iron; (c) hydrobromic acid with zinc; (d) acetic acid, HC2H3O2, with magnesium.

25. Based on the activity series (Table 4.5), what is the outcome of each of the following reactions?

  1. Al(s) + NiCl2(aq)

  2. Ag(s) + Pb(NO3)2(aq)

  3. Cr(s) + NiSO4(aq)

  4. Mn(s) + HBr(aq)

  5. H2(g) + CuCl2(aq)

26. The metal cadmium tends to form Cd2+ ions. The following observations are made: (i) When a strip of zinc metal is placed in CdCl2(aq), cadmium metal is deposited on the strip. (ii) When a strip of cadmium metal is placed in Ni(NO3)2(aq), nickel metal is deposited on the strip. (a) Write net ionic equations to explain each of the observations made above. (b) What can you conclude about the position of cadmium in the activity series? (c) What experiments would you perform to allow you to locate more precisely the position of cadmium in the activity series?

Additional Exercises

27. Suppose you have a solution that might contain any or all of the following cations: Ni2+, Ag+, Sr2+, and Mn2+. Addition of HCl solution causes a precipitate to form. After filtering off the precipitate, H2SO4 solution is added to the resultant solution and another precipitate forms. This is filtered off, and a solution of NaOH is added to the resulting solution. No precipitate is observed. Which ions are present in each of the precipitates? Which of the four ions listed above must be absent from the original solution?