Paired Exercise 9.17 Polychlorinated biphenyls (PCBs), which were formerly used

Question

Paired Exercise 9.17 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: 2 CpH4CL + 2302 + 2 H2O-+24 , + 12 HCI dy (a) How many moles of water are needed to react with 15.0 mol O2? mol H20 Use correct number of significant digits; the tolerance is +-1 in the 3rd significant digit (b) How many grams of HCI are produced when 16.8 mol H20 react? (c) How many moles of CO2 are produced when 78.3 g HCI are produced? C-0 mol CO2 Use correct number of significant digits; the tolerance is +-1 in the 3rd significant digit (d) How many grams of C12H4Cls are reacted when 102.75 g of CO2 are produced?Note: Use three significant digits in your answer. Use correct number of significant digits; the tolerance is +-1 in the 3rd significant digit (e) How many grams of HCl are produced when 3.0 kg C12H4Cl6 react?

Explanation / Answer

Part a)

Here, the ratio of O2 : H2O = 23:2

15 moles of O2 x 2 moles of H2O/23 moles of O2 = 1.3043 moles

moles of water = 1.3043 moles

Part b)

Ratio of H2O : HCl = 2:12

16.8 moles of H2O x 12 moles of HCl/2 moles of H2O = 100.8 moles

molar mass of HCl = 36.46 g/mole

Therefore, mass of HCl = 100.8 moles x 36.46 g/1 mole = 3675.16 g


Part c)

From the mass of HCl, moles of HCl can be calculated

78.3 g x 1 mole/36.46 g = 2.147 moles

Ratio of HCl : CO2 in balanced equation = 12:24

2.147 moles of HCl x 24 moles of CO2/12 moles of HCl = 4.294 moles

Moles of CO2 = 4.294 moles

Part d)

From the mass of CO2, moles of CO2 can be calculated

102.75 g x 1 mole/44.01 g = 2.334 moles

Ratio of CO2 : C12H4Cl6 in balanced equation = 24 : 2

2.334 moles of CO2 x 2 moles of C12H4Cl6/24 moles of CO2 = 0.194 moles

From the moles of C12H4Cl6, the mass of C12H4Cl6 can be calculated

0.194 moles x 360.86 g/mole = 70.0 g

Mass of C12H4Cl6 = 70.0 g

Part e)

Here, first, we need to convert kg to gram

3 kg = 3000 g

From the mass of C12H4Cl6, we the moles of C12H4Cl6 can be calculated

3000 g x 1 mole/360.86 g = 8.313 moles

Ratio of C12H4Cl6 : HCl in balanced equation = 2:12

8.313 moles of C12H4Cl6 x 12 moles of HCl/2 moles of C12H4Cl6 = 49.87 moles

From the moles of HCl, the mass of HCl can be calculated

49.87 moles x 36.46 g/mole = 1818.26 g

Grams of HCl = 1818.26 g

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