This set of Chemical Engineering Interview Questions and Answers focuses on “Analyses of Multicomponent Solutions and Mixtures”

1. What is the molecular weight of a mixture that contains 25% CO2, 40% O2 and 35% N2?

a) 11.2 g

b) 22.4 g

c) 33.6 g

d) 44.8 g

View answer

Explanation: Molecular weight = (25*44 + 40*32 + 35*28)/100 = 33.6 g.

2. What is the weight of 10 moles of a mixture with composition 15% O2, 25% SO2, 30% COCl2, 25% SO3 and 5% N2?

a) 124

b) 345

c) 507

d) 719

View answer

Explanation: Molecular weight of mixture = (15*32 + 25*64 + 30*99 + 25*80 + 5*28)/100 = 71.9, => Weight of mixture = 71.9*10 = 719.

3. If a compound contains 48% of Carbon, 48% of oxygen and 8% of hydrogen by weight, then what is the possible molecular formula of the compound?

a) C2H4O

b) CH4O3

c) C4H4O3

d) C4H8O3

View answer

Explanation: ratio of number of atoms, Carbon: Hydrogen: Oxygen = 48/12: 8/1: 48/16 = 4:8:3.

4. A compound contain 12% of carbon, 16% of oxygen, 28% of nitrogen, 4% of hydrogen and 40% calcium by weight, then what can be the possible formula of the compound?

a) C2H3N2Ca(OH)

b) CH4N4Ca2(OH)

c) CH3N2Ca2(OH)

d) None of the mentioned

View answer

Explanation: ration of number of atoms, carbon: hydrogen: oxygen: nitrogen: calcium = 12/12: 4/1: 16/16: 28/14: 40/20 = 1:4:1:2:2.

5. What is the value of x in C2H8(OH)x if the percentage by weight of hydrogen is 12%?

a) 1

b) 2

c) 3

d) 4

View answer

Explanation: Let the total weight of the compound be 100 g, => weight of hydrogen in the compound is 12 g, => x = 12 – 8 = 4.

6. 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

View answer

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.

7. 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

View answer

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.

8. 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

View answer

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.

9. 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

View answer

Explanation: Since it is a liquid mixture so the percentages are by weight, => average molecular weight of mixture = (20 + 30 + 35 + 15)/4 =25.

10. 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

View answer

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.

11. 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

View answer

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%.

12. 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

View answer

Explanation: Let the moles be 40 and 60, => mass of CO2 = 40*44 = 1760, mass of H2O = 1080, => mass percent of CO2 = 61.9%.

13. 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

View answer

Explanation: Let the moles be 20, 30 and 50, => mass percent of CO2 = (20*44)/[20*44 + 30*64 + 50*18] = 23%.

14. 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

View answer

Explanation: Mass percent of NaCl = 20*35.5/[20*35.5 + 30*16 + 50*18] = 34%.

15. 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

View answer

Explanation: Mass percent of CO2 = 10*28/[10*28 + 40*44 + 50*18] = 9.5%.

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