Questions and Problems

1. How do chemical equations relate to chemical reactions?

2. Summarize the information contained in the chemical equation below. How would this reaction be classified? CaCl₂(aq) + Na₂CO₃(aq)→CaCO₃(s) + 2NaCl(aq)

3. What are the meanings of (s), (l), (g), and (aq) after formulas in a chemical equation? What are the meanings of ∆ and←→?

4. What is wrong with balancing the chemical equation S + O₂→SO₃ as S + O₂→SO₂?

5. From your knowledge of chemistry and chemical formulas write the balanced equation for heating magnesium carbonate to give magnesium oxide and carbon dioxide, indicating the physical states of the reactants and products.

6. Balance the equation FeSO₄+ H₂SO₄+ O₂→Fe₂(SO₄)₃+ H₂O, which is for a reaction involved in the formation of pollutant acid mine water.

7. Balance each of the following: (a) C₂H₄+ O₂→CO₂+ H₂O, (b) KClO₄→KClO + O₂, (c)FeS₂+ O₂+ H₂O→FeSO₄+ H₂SO₄ (d) Fe₂O₃+ CO→Fe + CO₂, (e) H₃PO₄+ H2→PH₃ + H₂O, (f) P + Cl₂→PCl₅

8. Explain how chemical equations fit in with the general scheme of chemistry as a language.

9. A chemical equation that describes the action of hydrogen sulfide, H2S, dissolved in water isH2S←→H++ HS-. What does this equation say and how is it consistent with the fact that dissolved hydrogen sulfide is a weak acid?.

10. From the discussion of reactions of metals with sulfuric acid in Section 5.3 and your knowledge of the properties of silver jewelry, explain what is likely to happen when silver metal is placed in sulfuric acid.

11. Zinc is a very reactive metal. Explain with chemical equations what you would expect to happen if zinc metal were placed in sulfuric acid and what would happen if zinc oxide, ZnO, were placed in sulfuric acid.

12. Finely divided steel wool heated red hot and quickly placed into a bottle of oxygen burns vigorously undergoing the reaction 4Fe + 3O₂→2Fe₂O₃. Why is there no concern that a steel beam used in construction will burn in air? However, such a beam can be cut with an oxyacetylene torch by first heating a small portion of it with the torch, then turning off the acetylene and slowly running the torch across the beam. What is happening in this case?

13. A water solution of hydrogen peroxide, H₂O₂, is relatively stable. But, if a small quantity of solid manganese oxide is placed in the solution of hydrogen peroxide, bubbles are given off near the surface of the manganese oxide, although the solid appears to remain intact. Explain what happens and the role of the manganese oxide.

14. The following reactions were given in connection with the Solvay process used to makesodium bicarbonate and sodium carbonate: (A) NaCl + NH3+ CO₂+ H₂O→NaHCO₃(s) +NH₄Cl, (B) 2NaHCO₃+ heat→ Na₂CO₃+ H₂O(g) + CO2(g) (C) 3H₂+ N₂→2NH₃, (D) CaCO₃+ heat→CaO + CO₂, (E) CaO + H₂O→Ca(OH)₂. Classify each of these reactions in the categories given in Section 5.6.

15. Given the chemical reaction 4CH₄+ 6NO₂→4CO + 3N₂+ 8H₂O, write all the possible mole ratios relating N₂ to each of the other reaction participants.

16. Given the atomic masses N 14.0, H 1.0, and Cl 35.5 and the reaction below, calculate the mass of HCl produced when 12.7 g of NH₃ react.

2NH₃+ 3Cl₂→N₂+ 6HCl

17. Given the atomic masses C 12.0, H 1.0, and O 16.0 and the reaction below, calculate the mass of H₂O produced when 15.6 g of O₂react.

C₂H₄+ 3O₂→2CO₂+ 2H₂O

18. Match the reaction type from the list on the left with the example reaction from the right, below. PbSO₄ is insoluble in water.

A. Decomposition 1. HCl + NaOH→H2O + NaCl

B. Neutralization 2. Pb(NO₃)₂+ Na₂SO₄→PbSO₄+ 2NaCl

C. Substitution 3. 2H₂O₂→2H₂O + O₂

D. Double displacement 4. CuSO₄(aq) + Fe(s)→FeSO₄(aq) + Cu(s)

19. Of the following, the untrue statement is

A. The symbol←→is used to show that a reaction goes both ways.

B. The notation (l) is used to show that a reactant or product is dissolved in water.

C. A catalyst changes the rate of a reaction but is not itself consumed.

D. The symbol, ∆, is used to show application of heat to a reaction.

E. Simply because a chemical equation may be written and balanced does not indicate for certain that the chemical reaction it indicates will occur.

20. Given the reaction 2S + 3O₂→2SO₂ and atomic masses of 32.0 and 16.0 for S and O, respectively, calculate the mass of O₂ reacting with 15.0 g of S.

21. Given the reaction CH₄+ 2H₂O→CO₂+ 4H₂ and atomic masses of C, 12.0, H, 1.0; and O16.0, calculate the total mass of products formed when 24.0 g of CH₄ reacts.

22. Given the reaction 3CH₄+ 4Fe₂O₃→3CO₂+ 6H₂O + 8Fe and atomic masses of C, 12.0; H,1.0; Fe, 55.8; and O, 16.0, what is the mass of CO₂ produced by the reaction of 36.0 g of Fe₂O₃?

23. What is the basis of stoichiometry in respect to relative amounts of materials in reactions?

23. What are the major steps in doing a stoichiometric calculation?

24. What is a limiting reactant?

25. A solution of FeSO₄ was prepared by mixing 100 g of pure H₂SO₄ with water and putting it in contact with 50.0 g of iron metal. What reaction occurred? What masses of reaction products were generated and what were the masses of reactants, if any, left over? The atomic masses needed are H 1.0, Fe 55.8, S 32.0, and O 16.0.

26. What is the difference between the stoichiometric yield and the measured yield in a chemical reaction? How are they used to calculated percent yield?

27. How are titrations and stoichometry related?

28. A solid mineral sample consisting of calcium carbonate, CaCO₃, and nonreactive mineral matter weighing 0.485 g was stirred in some water to which 0.115 mol/L standard hydrochloric acid, HCl, was added from a buret. The reaction was CaCO₃+ 2HCl→CaCl₂+ CO₂+ H₂O. If 48.6 milliliters (0.0486 L) of HCl was required to react with all the CaCO₃ in the sample, what was the percentage of CaCO₃ in the sample given that the molar mass of CaCO₃ is 100 g/mol?

29. A 250 mL sample of incinerator exhaust gas scrubber water contaminated with HCl was titrated with 0.104 mol/L standard NaOH, of which 11.3 mL were required to reach the endpoint. What was the molar concentration of HCl in the water sample?

30. What is made by the Solvay process? What is the overall chemical reaction that describes the Solvay process? What are the two major raw materials consumed and what are two major species that are recycled through the process?

31. What are major green aspects of the Solvay process? What are some aspects that are less green?

32. What is a major alternative to use of the Solvay process?

33. Calculate the number of moles of total of AlCl₃ in 38.6 g of the compound and the number of moles of CH₄, in 217 g of methane. Use 27.0, 35.5, 12.0, and 1.0 for the atomic masses of Al, Cl, C, and H, respectively.

34. Why might you expect stoichiometric ratios of reactants to be used in industrial chemical reactions? If one of two reactants used in an industrial process is much more expensive than another, suggest why and in which way a stoichiometric ratio might not be used? Also, suppose that one of two reactants is quite toxic whereas the other reactant is not. Why might the practice of green chemistry suggest using a nonstoichometric ratio of reactants in such a case?

35. Given the reaction 2H₂+ O₂→2H₂O, identify which species is oxidized, which is reduced, which is the oxidizing agent, and which is the reducing agent.

36. Given the reaction that occurs when a direct electrical current is passed through liquid ionic NaCl, 2Na⁺+ 2Cl^-→2Na + Cl₂, identify which species is oxidized and which is reduced. Justify the answer.

37. Identify which reactions given in Section 5.6 are oxidation-reduction reactions