Mass Transfer

21.1 kg of a saturated aqueous solution of a highly soluble component A at 60°C is cooled to 25°C. The solubility limits of A are (0.6 kgA/kg water) at 60°C and (0.2 kgA/kg water) at 25°C. The amount in kg of the crystals formed is:

1. 0.4
2. 0.25
3. 0.2
4. 0.175

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22.A 25 cm × 25 cm × 1 cm flat sheet weighing 1.2 kg initially was dried from both sides under constant drying rate conditions. It took 1500 seconds for the weight of the sheet to reduce to 1.05 kg. Another 1m × 1m × 1cm flat sheet of the same material is to be dried from one side only. Under the same constant drying rate conditions, the time required for drying (in seconds) from its initial weight of 19.2 kg to 17.6 kg is

1. 1000
2. 1500
3. 2000
4. 2500

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23.A binary mixture of benzene and cyclohexane is separated by

1. Flash vaporisation
2. Extractive distillation
3. Solvent extraction
4. Ordinary distillation

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24.A coalescer in a mixer-settler liquid-liquid extraction column

1. Comprises of thin bed of substances of extended surface having high porosity
2. Helps in increasing the bubble size entering the settler
3. Helps in increasing the settling rate of the bubbles
4. All 'a', 'b', & 'c'

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25.A distillation column with N plates is being operated under normal conditions. At some point of time, the operation is shifted to total reflux condition (i.e., no product and residue are being withdrawn and feed to the column is stopped). At the new steady state,

1. Composition of vapors and that of liquid do not vary throughout the column
2. Reboiler load and condenser load are minimum
3. The top and bottom compositions are unchanged with and without total reflux
4. The top and bottom compositions correspond to the maximum enrichment available

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26.A good solvent used for absorption should not have very high

1. Viscosity
2. Vapor pressure
3. Freezing point
4. All (A), (B) & (C)

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27.A liquid mixture contains 30% o-xylene, 60% p-xylene and 10%. m-xylene (all percentages in w/w). Which of the following statements would be true in respect of this mixture?

1. The mixture exhibits an azeotrope at 101.3 kPa
2. The composition of the mixture, in percent by volume is: o-xylene 30, p-xylene 60. and mxylene 10
3. The composition of the mixture in mole percent is: o-xylene 30, p-xylene 60 and m-xyoene 10
4. The mixture contain optical isomers

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28.A minimum boiling azeotrope is exemplified by

1. Toluene-benzene
2. Acetone-carbon disulphide
3. Water-isobutyl alcohol
4. None of these

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29.A mixture of 10% C6H6 vapour in air at 25°C and 750 mm Hg has a dew point of 20°C. Its dew point at 30°C and 700 mm Hg will be around _________ °C.

1. 21.7
2. 20
3. 27.3
4. 18.7

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30.A natural draft cooling tower is filled with wooden grids, which covers about _________ percent of the tower height.

1. 42278
2. 30-40
3. 70-80
4. 90-100

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