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Weekly Quiz Competition

Question 1
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Directions For Questions

The vapour pressure of two pure liquids $$A$$ and $$B$$ which form an ideal solution are $$500$$ and $$800$$ torr respectively at $$300K$$. A liquid solution of $$A$$ and $$B$$ for which the mole fraction of $$A$$ is $$0.60$$ is contained in a cylinder closed by a piston on which the pressure can be varied. The solution is slowly vaporized at $$300K$$ by decreasing the applied pressure.

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The composition of vapour when first bubble formed is:

A
$$y_A = 0.6; y_B = 0.4$$

B
$$y_A = 0.48; y_B = 0.52$$

C
$$y_A = 0.52; y_B = 0.48$$

D
$$y_A = 0.5; y_B = 0.5$$

Solution
Question 2
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A liquid A and B form an ideal solution. If vapour pressure of pure A and B are $$500N{ m }^{ -2 }$$ and $$200N{ m }^{ -2 }$$ respectively, the vapour pressure of a solution of A and B containing 0.2 mole fraction of A would be:

A
$$700N{ m }^{ -2 }$$

B
$$300N{ m }^{ -2 }$$

C
$$260N{ m }^{ -2 }$$

D
$$140N{ m }^{ -2 }$$

Solution

Vapour pressure of a solution containing A & B liquid is
$$P_T=P_A+P_B$$
$$P_A= X_A-P^o_A$$ $$X_A$$= mole fraction of A; $$P^o_A$$= Pure vapour pressure of A.
$$\Rightarrow P_A= 0.2 \times 500 Nm^{-2}$$ & $$P_B= (1-0.2)\times 200 Nm^{-2}$$
Thus $$P_T= 0.2 \times 500 Nm^{-2} + 0.8 \times 200 Nm^{-2}$$
$$\Rightarrow P_T= 260 Nm^{-2}$$
Thus total vapour pressure of solution is $$260 Nm^{-2}$$ .
Question 3
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A mixture of ethyl alcohol and propyl alcohol has a vapour pressure of $$290\ mm$$ at $$300\ K$$. The vapour pressure of propyl alcohol is $$200\ mm$$. If the mole fraction of ethyl alcohol is $$0.6$$, its vapour pressure (in $$mm$$) at the same temperature will be:

A
$$300$$

B
$$700$$

C
$$360$$

D
$$350$$

Solution

By Roult's law,
$${ P }_{ T }={ P }_{ A }^{ \circ }{ x }_{ A }+{ P }_{ B }^{ \circ }{ x }_{ B }$$

$$\therefore \quad 290mm={ P }_{ A }^{ \circ }\times 0.6+200\times \left( 1-0.6 \right) $$

$$={ P }_{ A }^{ \circ }\times 0.6+80$$

$$\therefore \quad { P }_{ A }^{ \circ }=350\ mm$$

Hence, the correct option is $$D$$
Question 4
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A $$3.00\ L$$ oxygen gas is collected over water at $${27}^{o}C$$ when the barometric pressure is $$787\ Torr$$. If vapour pressure of water is $$27\ Torr$$ at $${27}^{o}C$$, moles of $$O_{2}$$ gas will be?

A
$$0.122$$

B
$$0.126$$

C
$$0.004$$

D
$$0.152$$

Solution

Given Volume (V)$$=3.00$$ L
Temperature(T)$$=27^{0}C=300 K$$
Barometric pressure$$=787$$ torr
Vapour pressure of water$$=27$$ torr
total pressure$$=787-27=760\quad{torr}=1\quad{atm}$$
Applying in ideal gas equation
PV=nRT
$$n=\dfrac{PV}{RT}$$
$$n=\dfrac{{1}\times{3}}{{0.0821}\times{300}}=0.122$$
Question 5
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The vapour pressure of pure water is 760 mm at $$25^{ 0 }C$$.The vapour pressure of solution containing 1(m) solution of glucose will be:

A
761.0 mm

B
746.5 mm

C
734.5 atm

D
746.5 Pa

Solution

Vapor pressure
$$\dfrac{P^{o}- P}{P^{o}}= \dfrac{W_{2}}{M_{2}} \times \dfrac{M_{1}}{W_{1}}$$

$$P^{o}= 760\ mm$$

$$M_{1} = 18$$

Molality $$(m)= 1m= \dfrac{mole\ of\ solute}{(weight)\ kg\ of\ solvent }= \dfrac{W_{2}/M_{2}}{W_{i} m \ gm}$$

$$\dfrac{760-P}{760} = 1 \times 10^{-3} \times 18$$

$$P= 746.5\ mm$$

Hence, the correct option is $$B$$
Question 6
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Which of the following is least soluble?

A
$$BeF_{2}$$

B
$$SrF_{2}$$

C
$$CaF_{2}$$

D
$$MgF_{2}$$

Solution

Here the option (B)$$Sr{ F }_{ 2 }$$ is correct, Which is least soluble.
Hydrogen energy decreases down the group, so solubility with the water decreases down the group.
Solubility in the order $$Be>Mg>Ca>Sr>Ba$$
Question 7
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Which of the following condition is not followed for an ideal solution?

A
$$\Delta { H }_{ mixing }$$=0

B
$$\Delta { S }_{ mixing }$$=0

C
$$\Delta { v }_{ mixing }$$=0

D
All A, B, and C are followed

Solution

An ideal solution satisfies the following conditions.
1)There will be no change in volume on mixing two components.
$$\triangle V_{mix}=0$$
2)There will be no charge in enthalpy on mixing two components.
$$\triangle H_{mix}=0$$
So, the $$\Delta S_{mixing}=0$$ is not followed by the ideal solution.
Question 8
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Which of the following pair will form an ideal solution?

A
Chlorobenzen , chloro ethane

B
Benzene, Toluene

C
Acetone, chloroform

D
Water, HCl

Solution

The substances that have similar structures and polarities form nearly ideal solution benzene and toulene will form an ideal solution.
Acetone, chloroform, chlorobenzene chloroethane ,water $$HCl$$ will form non-ideal solutions due to the difference of polarites between the two components.
Question 9
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$$3$$ moles of $$P$$ and $$2$$ moles of $$Q$$ are mixed, what will be their total vapour pressure in the solution if their partial vapour pressures are $$80$$ and $$60$$ respectively?

A
$$80$$ torr

B
$$140$$ torr

C
$$720$$ torr

D
$$70$$ torr

Solution

Mole fraction of $$P=\dfrac { 3 }{ 3+2 } =\dfrac { 3 }{ 5 } $$

Mole fraction of $$Q=\dfrac { 2 }{ 3+2 } =\dfrac { 2 }{ 5 } $$

Hence,

Total vapour pressure =(Mole fraction of $$P$$ $$\times $$ Vapour pressure of $$P$$) + (mole fraction of $$Q$$ $$\times$$ Vapour pressure of $$Q$$)

$$=\left( \dfrac { 3 }{ 5 } ×80 \right) +\left( \dfrac { 2 }{ 5 } ×60 \right) =48+24=72\ torr$$
Question 10
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How many grams of sucrose must be added to $$320g$$ of water to lower the vapour pressure by $$1.5mm$$ $$Hg$$ at $${25}^{o}C$$?
(Given: The vapour pressure of water at $${25}^{o}C$$ is $$23.8mm$$ $$Hg$$ and molar mass of sucrose is $$324.3g/mol$$)

A
$$21.5g$$

B
$$140g$$

C
$$363.36g$$

D
$$160.12g$$

Solution

$$w_{1}=$$ Wsucrose = ?
$$M_{1}=$$ Molecular weight $$+32,4.3\ g/mol$$
$$w_{2}=320\ g$$
$$M_{2}=H_{2}O=18\ g/mol$$
$$p-ps=1.5\ mm$$
$$p=23.8\ mm$$
$$\dfrac{p-ps}{p}=\dfrac{W_{1}}{M_{1}}\times \dfrac{M_{2}}{W_{2}}$$
$$\dfrac{1.5}{23.8}=\dfrac{W_{1}}{324.3}\times \dfrac{18}{320}$$
$$W_{1}=363.36\ g$$

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Question 1

$$y_A = 0.6; y_B = 0.4$$

$$y_A = 0.48; y_B = 0.52$$

$$y_A = 0.52; y_B = 0.48$$

$$y_A = 0.5; y_B = 0.5$$

Solution

Question 2

$$700N{ m }^{ -2 }$$

$$300N{ m }^{ -2 }$$

$$260N{ m }^{ -2 }$$

$$140N{ m }^{ -2 }$$

Solution

Question 3

$$300$$

$$700$$

$$360$$

$$350$$

Solution

Question 4

$$0.122$$

$$0.126$$

$$0.004$$

$$0.152$$

Solution

Question 5

761.0 mm

746.5 mm

734.5 atm

746.5 Pa

Solution

Question 6

$$BeF_{2}$$

$$SrF_{2}$$

$$CaF_{2}$$

$$MgF_{2}$$

Solution

Question 7

$$\Delta { H }_{ mixing }$$=0

$$\Delta { S }_{ mixing }$$=0

$$\Delta { v }_{ mixing }$$=0

All A, B, and C are followed

Solution

Question 8

Chlorobenzen , chloro ethane

Benzene, Toluene

Acetone, chloroform

Water, HCl

Solution

Question 9

$$80$$ torr

$$140$$ torr

$$720$$ torr

$$70$$ torr

Solution

Question 10

$$21.5g$$

$$140g$$

$$363.36g$$

$$160.12g$$

Solution

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