Heat Transfer Operations Multiple Choice Questions on “Evaporators – Duhring’s Rule”.
1. The Duhring’s rule is used to determine _______
a) Osmotic pressure
b) Surface tension
c) Boiling point elevation
d) Vapour pressure depression
Answer: c
Clarification: The Duhring’s rule is used to determine the boiling point of a solution at a particular concentration of solute by assuming that the relation between boiling point solution and solvent is a linear function.
2. The Duhring’s rule states that: The boiling point of a given solution is a _____ function of the boiling point of water at the same temperature.
a) Linear
b) Parabolic
c) Exponential
d) Quadratic
Answer: a
Clarification: The Duhring’s rule is used to determine the boiling point of a solution at a particular concentration of solute by assuming that the relation between boiling point solution and solvent is a linear function. It is also necessary to consider that the solution follows Roult’s Law.
3. If the concentration of the solution increases, the Lines shift __________
a) To the left
b) To the right
c) Downwards
d) Upwards
Answer: d
Clarification: The parallel lines of Duhring’s plot are for particular solution concentrations which when increased shifts upwards.
4. What are the names of the axes in the plot by Duhring?
a) X –Concentration of solution, Y- Boiling Point of solution
b) X –Boiling Point of pure water, Y- Boiling Point of solution
c) X –Boiling Point of Solution, Y- Concentration of solution
d) X –Boiling Point of solution, Y- Boiling Point of pure water
Answer: b
Clarification: The Duhring’s plot is made between boiling point of pure water as the abscissa and boiling point of solution as the ordinate.
5. For Duhring’s Plot to be valid, the range of boiling points must be relatively ________
a) Narrow
b) Large
c) Very big
d) Negligibly small
Answer: a
Clarification: The duhring’s plot should be applied keeping in mind few important concepts of its applications, which is, it cannot be applied for large elevations of BP as well as the solution should follow Roults Law.
6. For Duhring’s plot to be valid and to see its applicability to an operation, we must check if the solution in feed follows __________
a) Henry’s Law
b) Roults law
c) Avogadro’s Law
d) Gas Laws
Answer: b
Clarification: The Duhring’s rule is used to determine the boiling point of a solution at a particular concentration of solute by assuming that the relation between boiling point solution and solvent is a linear function. It is also necessary to consider that the solution follows Roult’s Law.
7. The slope of the Duhring’s Plot is always ______
a) Greater than one
b) Greater than 2
c) Less than 1
d) Less than zero
Answer: a
Clarification: The Duhring’s plot is done between boiling point of pure water as the abscissa and boiling point of solution as the ordinate. Hence the slope is = B.P.of solution/B.P.of pure water >1 as the B.P.of solution is always greater than B.P.of pure water.