Food Processing Unit Operations Multiple Choice Questions on “Evaporation – Boiling Point Elevation ”.
1. Which law governs theboiling point elevation in evaporators?
a) Rauolt’s law
b) Boyle’s law
c) Charle’s law
d) Duhring’s law
Answer: d
Clarification: Duhring’s law is the ratio of temperature at which two solutions exert the same temperature is constant which can be used to determine boiling point elevation in evaporators.
2. Why does boiling point elevation occur?
a) Due to addition of solute
b) Due to addition of solution
c) Due to change in humidity
d) Due to change in pressure
Answer: a
Clarification: Boiling point elevation is the temperature change of the boiling point of a solvent caused by adding a solute. If the vapor pressure is lowered, the relative number of particles becoming a gas is decreased. In order to reach equilibrium between vapor pressure and atmospheric pressure, more energy is added to force the particles at the surface of the liquid to release to the gaseous state. This increase results in the liquid boiling at a higher temperature.
3. What is boiling point elevation constant of water?
a) 5.12°C/m
b) 51.2°C/m
c) 0.512°C/m
d) 0.0512°C/m
Answer: c
Clarification: The boiling point elevation constant of water is 0.512°C/m. It is a constant that is equal to the change in the boiling point for a 1-molal solution of a nonvolatile molecular solute so therefore it is called as the molal boiling-point elevation constant.
4. What is the boiling point of sugar?
a) 1,465°C
b) 100°C
c) 102.82°C
d) 78.37°C
Answer: c
Clarification:The boiling point of sugar is 102.82°C. The boiling point of salt is 1,465C°. The boiling point of pure water is 100°C. The boiling point of ethanol is78.37°C.
5. How does boiling point depend on pressure?
a) Directly proportional
b) Indirectly proportional
c) Not dependent
d) Depends on the solute
Answer: a
Clarification: The boiling point relates to the temperature when the vapor pressure of the liquid equals the surrounding environmental pressure. Thus, the boiling point is dependent on the pressure. The boiling point increases with increase in the pressure up to the critical point.
6. Can the boiling point be reduced below the triple point?
a) True
b) False
Answer: b
Clarification: The boiling point cannot be reduced below the triple point. Since the boiling point is dependent on the pressure. It decreases with decreasing pressure until the triple point is reached.
7. Which liquid has lowest boiling point?
a) Helium
b) Water
c) Ethanol
d) Nitrogen
Answer: a
Clarification:Helium has the lowest boiling point which is -268.9°C. Water has boiling point of 100°C. Ethanol has the boiling point of78.37°C. Nitrogen has boiling point of -195.8°C.
8. Which of the following are factors that regulate the boiling point of the solute?
a) Concentration of solute in the solution
b) Concentration of solvent
c) Type of solute
d) Type of solvent
Answer: a
Clarification: The boiling point of a solution is a colligative property therefore it depends on the concentration of solute in the solution, but not on type of solute or solvent.
9. What is the alternative name for boiling point elevation?
a) Vapor pressure lowering
b) Vapor pressure elevation
c) Latent heat
d) Entropy
Answer: a
Clarification: Vapor pressure lowering is the alternative name for boiling point elevation. The vapor pressure of an aqueous solution is less than that of pure water at the same temperature. Therefore the boiling point of the solution will be higher than that of the water.
10. Is boiling point a physical property?
a) True
b) False
Answer: a
Clarification: Boiling point is a physical property. Physical properties are properties that can be measured without changing the chemical nature of the substance.