Polychlorinated biphenyls (PCBs), which were formerly used in the manufacture of
ID: 796538 • Letter: P
Question
Polychlorinated biphenyls (PCBs), which were formerly used in the manufacture of electrical transformers, are environmental and health hazards. They break down very slowly in the environment. The decomposition of PCBs can be represented by the equation:
2C12H4Cl6 + 23O2 + 2H2O Yields 24CO2 + 12HCl
a) How many moles of water are needed to react 10.0 mol O2?
b) How many grams of HCl are produced when 15.2 mol H2O react?
c) How many moles of CO2 are produced when 76.5 g HCl are produced?
d) How many grams of C12H4Cl6 are reacted when 100.25 g CO2 are produced?
e) How many grams of HCl are produced when 2.5 kg C12H4Cl6 react?
Explanation / Answer
a)
10 moles of O2 x 2 moles of H2O / 23 moles of O2 = 0.870 moles of H2O
b)
15.2 moles of H2O x 12 moles of HCl / 2 moles of H2O = 91.2 moles of HCl
91.2 moles x 36.46 g / mol = 3,325 g of HCl
c)
76.5 g x 1 mol / 36.46 g = 2.10 moles of HCl
2.10 moles of HCl x 24 moles of CO2 / 12 moles of HCl = 4.2 moles of CO2
d)
100.25 g x 1 mol / 44.01 g = 2.28 moles of CO2
2.28 moles of CO2 x 2 moles of C12H4Cl6 / 24 moles of CO2 = 0.190 moles of C12H4Cl6
0.190 moles x 360.88 g / mol = 68.6 g of C12H4Cl6
e)
2.5 kg x 1,000 g / 1 kg = 2,500 g of C12H4Cl6
2,500 g x 1 mol / 360.88 g = 6.93 moles of C12H4Cl6
6.93 moles of C12H4Cl6 x 12 moles of HCl / 2 moles of C12H4Cl6 = 41.6 moles of HCl
41.6 moles x 36.46 g / mol = 1,517 g of HCl
Hope this helps and good luck! :)