2CSC (p.181) #13-21

7/16/13

13. a. 6 moles of NH3 are needed to react with 9 mol PbO.
      b. 5 moles of N2 are produced by the reaction of 10 mol NH3.
      c. 5 moles of Pb are produced from 5 mol PbO.

14. a. 1 mole
      b. 621g
      c. 28g
      d. 415g

15. The percent oxygen by mass is not 67%, it is 73%. This is because the molar mass of oxygen is 32, and the molar mass of carbon is 12 in carbon dioxide. Therefore, 32/44 x 100= 73% oxygen.

16. a. 87% silver by mass
         (108 x 2) + 32= 248
         216/248 = .870 x 100 = 87%
      b. 53% aluminum by mass
          (27 x 2) + (16 x 3)= 102
          54/102 = .53 x 100 = 53%
      c. 40% calcium by mass
          40 + 12 + (16 x 3) = 100
          40/100 = .40 x 100 = 40%

17. a. 68% lead by mass
         207 + 32 + (16 x 4) = 303
         207/303 = .68 x 100 = 68%
     b. 10% PbSO4 in the ore sample
          5/50 = .1 x 100 = 10%
     c. 6.8% Pb in the total ore sample
        68 x 10% (.10) = 6.8%
    d.

10% lead in the PbSO4 ore

68% lead in lead sulfate

18. a. Reusing is when you use something over and over again until it can't be used anymore. Recycling is when recourses can be used again and processed to be used for a different purpose.
      b. Two examples of reusing are using a plastic fork over and cleaning it, instead of throwing it away. And reusing water bottles is an example. Two examples of recycling are old computer and car parts and cans.

19. a. Renewable resources: plants, animals, fertilizer, water, and air
      b. Nonrenewable resources: metals, natural gas, coal, petroleum/ oil

20. a. reusing
      b. recycling
      c. reusing

21. Both glass from a light bulb and paper from a newspaper can be recycled. However, a newspaper can be reused as well, but a light bulb cannot not.