# Mass Transfer Questions and Answers – Humidification-Vapour-Gas Mixture

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This set of Mass Transfer Questions & Answers for experienced focuses on “Humidification-Vapour-Gas Mixture “.

1. Partial pressure equals vapour pressure if it is___________
a) Saturated
b) Unsaturated
c) Isothermal
d) None of the mentioned

Explanation: At saturation, the vapour-gas mixture will be at equilibrium so the vapour pressure equals partial pressure.

2. Say True or False
I) Vapour- at superheated temperature
II) Gas – at condensation temperature
a) True
b) False

Explanation: Since vapour has liquid portion we cannot say superheated. Superheated means free from other components like unique gas.

3. Guess the saturated molar absolute humidity of the gas(A.- Vapour(B. mixture at 100 degree Celsius. Vapour pressure of A is 300 mmHg and the total pressure is 760 mmHg.
a) 0.39
b) 0.65
c) 0.60
d) Cannot determine

Explanation: Saturated molar humidity= Vapour pressure of A/ Vapour pressure of B
= 300/(760-300) =0.65.

4. The system is unsaturated if partial pressure _________ equilibrium vapour pressure.
a) Less than
b) Greater than
c) Equals to
d) All of the mentioned

Explanation: If saturated, the vapour pressure equals partial pressure. If unsaturated, the pressure will be less than vapour pressure.

5. Consider a saturated gas(A.-vapour(B. mixture , if the absolute molal humidity is 0.265 and the total pressure= 760 mmHg. Find the vapour pressure of B.
a) 149.21 mmHg
b) 159.21 mmHg
c) 169.21 mmHg
d) 600.8 mmHg

Explanation: First, we have to find the vapour pressure of A.
0.265= pA/760-pA
pA= 159.21
pB=760-159.21= 600.8.

6. The vapour pressure of the nitrogen gas is 400mmHg and the partial pressure is 300mmHg. Find the relative saturation.
a) 75
b) 133
c) 100
d) 50

Explanation: Relative saturation or relative humidity = (partial pressure/vapour pressure. x100
=75.

7. Thermometer measurement temperature is
a) Dry bulb temperature
b) Wet bulb temperature
c) Dew point temperature
d) Room temperature

Explanation: Dry bulb temperature is the actual measuring temperature of the thermometer.

8. Find the dew point a) X
b) Y
c) Z
d) None of the mentioned

Explanation: The point at 100% saturation is known as dew point. Below the point, the vapour starts to condense.

9. Temperature at which the partial pressure of the gas-vapour mixture equals vapour pressure _______
a) Dry bulb temperature
b) Wet bulb temperature
c) Dew point temperature
d) None of the mentioned

Explanation: At saturation, the vapour pressure equals partial pressure. At dew point, saturation attains.

10. Check whether we get approximately 80% saturation if the total pressure and the partial pressure of the gas mixture is 760 mmHg and 260 mmHg. Also, the vapour pressure is 300 mmHg.
a) True
b) False  