0100-4-pc-1mark

In a paper mill, a wash liquor containing 3% (by weight) solids is concentrated in an evaporator to yield a lye containing 30% (by weight) solids. The quantity of water evaporated per 100 kg of feed is:

• 30 kg
• 70 kg
• 60 kg
• 90 kg

GATE-CH-1993-8-a-pc-2mark

1000 kg of a solution containing 50% by weight of a salt dissolved in it is cooled. 400 kg of anhydrous salt is separated out. The solubility of the salt at the lower temperature in kg/100kg of water is

• 80

• 50

• 40

• 20

GATE-CH-1995-2-f-pc-2mark

1000 kg of wet solids are to be dried from 60% to 20% moisture (by weight). The mass of moisture removed in kg is

• 520

• 200

• 400

• 500

GATE-CH-2003-40-pc-2mark

Air at a temperature of 20^oC and 750 mm Hg pressure has a relative humidity of 80%. What is its percentage humidity? Vapor pressure of water at 20^oC is 17.5 mm Hg.

• 80.38
• 80
• 79.62
• 78.51

GATE-CH-1989-1-i-pc-2mark

1000 kg of a solution containing 30% solids is concentrated to 60% solids. The amount of water evaporated is ––––- kg.

• Answer

GATE-CH-1991-2-i-pc-2mark

A wet paper pulp contains 75% water. After 100 kg of water is removed in a dryer, it is found that the pulp is now containing 30% water. The weight of the original pulp (in kg) is ––––-

• Answer

GATE-CH-1991-2-ii-pc-2mark

The weather bureau reports a dry bulb temperature of ambient air as 29\(^\circ \)C and relative humidity of 80%. The barometer reads 750 mm Hg. The percent humidity of the ambient air is ––––-
(Vapor pressure of water at 29\(^\circ \)C = 30 mm Hg)

• Answer

GATE-CH-1992-2-a-pc-2mark

It is desired to make 100 kg of a solution containing 40% salt by mixing solution \(A\) containing 25% salt and solution \(B\) containing 50% salt. The mass in kg of solution \(A\) required is ––––-

• Answer

GATE-CH-1990-1-i-pc-4mark

A mixture of ethyl acetate vapor and air has a relative saturation of 50% at 30\(^\circ \)C and a total pressure of 100 kN/m\(^2\). If the vapor pressure of ethyl acetate at 30\(^\circ \)C is 16 kN/m\(^2\). 

(i) The percentage of air is ––––-
{#1}

(ii) The percentage saturation is ––––-
{#2}

GATE-CH-2002-2-12-pc-2mark

1 kg of a saturated aqueous solution of a highly soluble component \( A \) at 60^oC is cooled to 25^oC. The solubility limits of \( A \) are (0.6 kg \( A \))/(kg water) at 60^oC and (0.2 kg \( A \))/(kg water) at 25^oC. The amount, in kg, of the crystals formed is

• 0.4
• 0.25
• 0.2
• 0.175

GATE-CH-2003-41-pc-2mark

Na₂SO₄.10H₂O crystals are formed by cooling 100 kg of 30% by weight aqueous solution of Na₂SO₄. The final concentration of the solute in the solution is 10%. The weight of crystals is

• 20
• 32.2
• 45.35
• 58.65

GATE-CH-2004-39-pc-2mark

80 kg of Na₂SO₄ (molecular weight = 142) is present in 330 kg of an aqueous solution. The solution is cooled such that 80 kg of Na₂SO₄.10H₂O crystals separate out. The weight fraction of Na₂SO₄ in the remaining solution is

• 0.00
• 0.18
• 0.24
• 1.00

GATE-CH-2008-32-pc-2mark

A 35 wt% Na₂SO₄ solution in water, initially at 50^oC, is fed to a crystallizer at 20^oC. The product stream contains hydrated crystals Na₂SO₄.10H₂O in equilibrium with a 20 wt% Na ₂SO₄ solution. The molecular weights of Na₂SO₄ and Na₂SO₄.10H₂O are 142 and 322, respectively. The feed rate of the 35% solution required to produce 500 kg/h of hydrated crystals is

• 403 kg/h
• 603 kg/h
• 803 kg/h
• 1103 kg/h

GATE-CH-2010-32-pc-2mark

A saturated solution at 30^oC contains 5 moles of solute (M.W. = 50 kg/kmol) per kg of solvent (M.W. = 20 kg/kmol). The solubility at 100^oC is 10 moles of the solute per kg of the solvent. If 10 kg of the original solution is heated to 100^oC, then the weight of the additional solute that can be dissolved in it, is

• 0.25 kg
• 1 kg
• 2 kg
• 3.34 kg

GATE-CH-1988-1-ii-c-pc-1mark

1000 kg of solution containing 50% by weight of a salt dissolved in it is cooled, whereupon 400 kg of anhydrous salt is crystallized out. The solubility of salt at lower temperature in kg/100 kg of water is ––––-

• Answer

GATE-CH-1991-12-i-pc-6mark

Nitrogen from a cylinder is bubbled through acetone at 1.1 bar and 323 K at the rate of \(2 \times 10^{-4}\) m\(^3\)/min. The nitrogen, saturated with acetone vapor leaves at 1.013 bar, 308 K at the rate of \(3.83 \times 10^{-4}\) m\(^3\)/min. What is the vapor pressure (in bar) of acetone at 308 K?

• Answer

GATE-CH-1998-12-pc-5mark

1000 kg/h of an aqueous solution of 20% \(\ce {Na2CO3}\) is cooled gradually to \(T^\circ \)C, to crystallize out \(\ce {Na2CO3.10H2O}\). The solubility of \(\ce {Na2CO3}\) at \(T^\circ \)C is 2.1%. Calculate the percentage of \(\ce {Na2CO3}\) recovered in the form of crystals. (Assume no loss of \(\ce {Na2CO3}\) through the mother liquor adhering to the crsytals and no carry over of crystals with the mother liquor). Draw a neat block diagram showing the inlet and exit compositions and flow rates. (Molecular weight of \(\ce {Na2CO3}\) can be assumed to be 106 and that of water to be 18).

• Answer

GATE-CH-2017-30-pc-2mark

An aqueous salt-solution enters a crystallizer operating at steady state at 25^oC. The feed temperature is 90^oC and the salt concentration in the feed is 40 weight%. The salt crystallizes as a pentahydrate. The crystals and the mother liquor leave the crystallizer. The molecular weight of the anhydrous salt is 135. The solubility of the salt at 25^oC is 20 weight%.

The feed flow rate required for a production rate of 100 kg/s of the hydrated salt, sounded to the nearest integer, is _______ kg/s.

• Answer

GATE-CH-1999-7-pc-5mark

\(\ce {CaCO3}\) slurry has to be dried. The dryer is designed to remove 100 kg moisture per hour. Air at 20\(^\circ \)C and 40% relative humidity, enters the dryer and leaves at 65\(^\circ \)C and 65% relative humidity. (i) What is the weight (in kg) of bone-dry air required per hour? The atmospheric pressure is 103 kPa. (ii) If the humidity of the air entering can be varied, what is the minimum amount of dry air (in kg/h) required? The constants for Antoine equation for vapor pressure of water in mm Hg may be taken as \(A = 18.306\), \(B = 3816.44\) and \(C = -46.13\).
(i) ____________
{#1}

(ii) ____________
{#2}

0100-6-pc-5mark

The figure below is a schematic of a process for the production of NaOH cake which is used in households to clear plugged drains in the plumbings (all compositions in weight%).

The fresh feed to the process is 10,000 kg/h of a 40% aqueous NaOH solution. The fresh feed is combined with the recycled filtrate from the crystallizer, and fed to the evaporator where water is removed to produce a 50% NaOH solution, which in turn is fed to the crystallizer. The crystallizer produces a filter cake that is 95% NaOH crystals and 5% solution that itself consists of 45% NaOH. The filtrate contains 45% NaOH.

1. You are asked to determine the flow rate of water removed by the evaporator, and the recycle rate for this process.

2. Assume that the same production rate of NaOH cake occurs, but the filtrate is not recycled. What would be the total feed rate of 40% NaOH have to be then? Assume that the product solution from the evaporator still contains 50% NaOH.

• Answer

GATE-CH-1994-2-j-pc-1mark

A gas bubble at a pressure of \(P_g\) is passed through a solvent with a saturation vapor pressure of \(P_s\). If the time of passage of the bubble is long and air is insoluble in the solvent, the mole fraction of solvent in the bubble will be equal to ––––-

• Answer

GATE-CH-1994-2-l-pc-1mark

A super saturated solution of a sparingly soluble solute, at a concentration of \(C\), is being fed to a crystallizer at a volumetric flow rate of \(V\). The solubility of the solute is \(C_s\). The output rate of solids from an efficient crystallizer is ––––-

• Answer