Chemistry Homework #4

Electrical current

Pg 151 #9-22

9.     Why are active metals more difficult to process and refine than are less active metals?

a.     Active metals are more difficult to process and refine than are less active metals because if they are active, they react at varying degrees with oxygen.

10. Based on your results from Investigating Matter B.5 (page 142), which metals involved in that investigation would be the easiest to process? Why?

a.     The metals involved in the investigation that would be the easiest to process would be copper and zinc because they were the least reactive with all of the solutions added to the metals.

11. Why do most metals exist in nature as minerals rather than as pure metallic elements?

a.     They exist in nature as minerals rather than pure metallic elements because of their reactivity with other substances, as well as their reactivity with oxygen.

12. Which of these reactions is more likely to occur? Why? (Refer to Table 2.5 page 145).

a.     Calcium metal with Chromium (III) chloride           

                                               i.     This is because the reactivity of calcium metal is higher than that of chromium metal.

b.     Chromium metal with calcium chloride

13. Consider the following two equations. Which equation represents a reaction that is more likely to occur? Why?

a.     Zn²⁺(aq) + 2 Ag(s) => Zn(s) + 2 Ag⁺(aq)

b.     2 Ag⁺(aq) + Zn(s) => 2 Ag(s) + Zn²⁺(aq)

                                               i.     This is because there are more molecules of silver, a less reactive metal, to affect the zinc.

14. A. Why would it be a poor idea to stir a solution of lead (II) nitrate with an iron spoon?

a.     It would be a poor idea to stir it with an iron spoon because the iron that makes up the spoon is more reactive than the lead nitrate, which would cause a chemical reaction and change the chemical makeup of the spoon.  

B. Write a chemical equation to support your answer.

       a.    Fe³⁺(s) + Pb²⁺(l) => Fe(l) + Pb⁺(s)

15. Define oxidation and reduction in terms of electron transfer.

a.     OXIDATION: losing one or more electrons

b.     REDUCTION: gaining one or more electrons

16. Write an equation for each of the following processes.

a.     The reduction of gold(III) ions to gold metal

                                               i.     Au³⁺ + 3 e-  => Au

b.     The oxidation of elemental vanadium to vanadium(IV) ions

                                               i.     V => V⁴⁺ + 4 e-

c.      The oxidation of Cu⁺ to Cu²⁺ ions           

                                               i.     Cu + 2 Ag⁺ => Cu²⁺ + 2 Ag

17. Identify each of the following equations as representing either an oxidation reaction or a reduction reaction:

a.     Fe²⁺+ 2 e - => Fe

                                               i.     Reduction

b.     Cr => Cr³⁺ + 3 e-

                                               i.     Oxidation

c.      Al³⁺ + 3 e - => Al

                                               i.     Reduction

18. Consider the following equation:           

Zn(s) + Ni²⁺(aq) => Zn²⁺(aq) + Ni(s)

a.     Which reactant has been oxidized? Explain your choice.

                                              i.     Zinc was oxidized because it lost two electrons when looking at the end product.

b.    Which reactant has been reduced? Explain your choice.

                                              i.     The Nickel was reduced because it gained the two electrons that Zinc lost.

c.     What is the reducing agent in this reaction?

                                              i.     Zinc

19. Consider the following equation:

2 K(s) + Hg²⁺(aq) => 2 K⁺(aq) + Hg(s)

a.     Which reactant has been oxidized? Explain your answer.

                                              i.     Potassium was oxidized because it lost one electron when looking at the end product.

b.    Which reactant has been reduced? Explain your answer.

                                              i.     Mercury was reduced because it became a neutral substance.

c.     What is the oxidizing agent in this reaction?

                                              i.     Potassium

20. Write an equation for:

a.     The oxidation of Al metal by Cr³⁺ ions.

                                              i.     Al + Cr³⁺ => Al³⁺ + Cr

b.    The reduction of Mn²⁺ ions by Mg metal.

                                              i.     Mn²⁺ + Mg => Mg²⁺ + Mn

21. Explain how each of the following processes converts metal cations into metal atoms.

a.     Electrometallurgy:

                                              i.     Using an electrical current to supply electrons to metal ions, thus reducing them.

b.    Pyrometallurgy:

                                              i.     The oldest ore-processing method, which involves treating the metals and their ores with heat (thermal energy), an in a blast furnace.

c.     Hydrometallurgy:

                                              i.     Involves treating ores and other metal-containing materials with reactants in a water solution.

22. What processes would be most useful in obtaining the following elements from their ores?

a.     Magnesium:

                                              i.     Electrometallurgy

b.    Lead:

                                              i.     Pyrometallurgy