1. If hydrogen is 14% by weight in CH3(OH)x(NH3)y, then what is the possible value of x*y?
a) 6
b) 12
c) 18
d) 24
Explanation: Let the weight of compound be 100 g, => weight of hydrogen = 14 g, => 3y + x + 3 = 14 => 3y + x = 11, => and 12 + 14 + 16x + 14y = 100, => 8x + 7y = 37, solving both equations we get x = 2 and y = 3, => x*y = 6.
2. A liquid mixture of O2, CH4 and CO has the composition 32% O2, 16% CH4 and 52% CO, then what is the mole fraction of CH4?
a) 0.1
b) 0.2
c) 0.25
d) 0.5
Explanation: Let the total weight of the mixture be 100 g, => weight of each component are 32 g, 16 g and 52 g respectively, => moles of O2 = 32/16 = 2, moles of CH4 = 16/16 = 1, moles of CO = 52/26 = 2 g, => mole fraction of CH4 = 1/5 = 0.2.
3. A gaseous mixture is composed of 20% CO2, 40% O2 and 40% N2. What is the mass fraction of N2?
a) 0.307
b) 0.416
c) 0.529
d) 0.784
Explanation: Let the total moles of the mixture be 100, => mass of CO2 = 20*44 = 880 g, mass of ¬O2 = 40*16 = 640 g, mass of N2 = 40*14 = 560 g, => mass fraction of N2 = 560/(880 + 640 + 560) = 0.307.
4. A liquid mixture composed of 20% CH4, 30% C2H4, 35% C2H2, and 15% C2H2O. What is the average molecular weight of the mixture?
a) 20
b) 25
c) 6.75
d) 9.25
Explanation: Since it is a liquid mixture so the percentages are by weight, => average molecular weight of mixture = (20 + 30 + 35 + 15)/4 =25.
5. A gaseous mixture composed of 20% CH4, 30% C2H4, 35% C2H2, and 15% C2H2O. What is the average molecular weight of the mixture?
a) 20
b) 25
c) 6.75
d) 9.25
Explanation: Since it is a gaseous mixture so the percentages are by mole, => average molecular weight of mixture = {(20/100)*16 + (30/100)*28 + (35/100)*26 + (15/100)*42}/4 = 6.75.
6. The mole percent of H2 and N2 in a mixture is 50% each, what is the mass percentage of H2?
a) 12.5
b) 25
c) 50
d) 87.5
Explanation: Let the moles be 50 each, => Mass of H2 = 100, Mass of N2 = 700, => Mass percentage of H2 = 100/(100 + 700)*100 = 12.5%.
7. The mole percent of CO2 and H2O in a mixture is 40% and 60% respectively, what is the mass percent of CO2?
a) 24.1
b) 47.2
c) 61.9
d) 78.5
Explanation: Let the moles be 40 and 60, => mass of CO2 = 40*44 = 1760, mass of H2O = 1080, => mass percent of CO2 = 61.9%.
8. A mixture contains 20% CO2, 30% SO2 and 50% H2O, what is the mass percent of CO2?
a) 23
b) 45
c) 66
d) 87
Explanation: Let the moles be 20, 30 and 50, => mass percent of CO2 = (20*44)/[20*44 + 30*64 + 50*18] = 23%.
9. A mixture contains 20% NaCl, 30% CH4 and 50% H2O, what is the mass percent of NaCl?
a) 21
b) 34
c) 45
d) 68
Explanation: Mass percent of NaCl = 20*35.5/[20*35.5 + 30*16 + 50*18] = 34%.
10. A mixture contains 10% CO, 40% CO2 and 50% H2O, what is the mass percent of CO2?
a) 9.5
b) 15.4
c) 39.5
d) 74.1
Explanation: Mass percent of CO2 = 10*28/[10*28 + 40*44 + 50*18] = 9.5%.