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CBSE Questions for Class 11 Engineering Chemistry States Of Matter Quiz 15 - MCQExams.com
CBSE
Class 11 Engineering Chemistry
States Of Matter
Quiz 15
Two liquids A and B form an ideal solution. the solution has a vapor pressure of 700 torrs at $$ 80^0 C $$. it is distilled till 2/3rd of the solution is collected as condensate. the composition of the condensate $$ x'_A = 0.75 $$. and that of residue is $$ x''_A = 0.30 $$ if the vapor pressure of the residue at $$ 80^0 C $$ is 600 torr. which of the following is/are true?
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The composition of the original liquid was $$ x_A = 0.6 $$
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The composition of the original liquid was $$ x_A = 0.4 $$
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$$ P^0_A = \frac {2500}{3} Torr $$
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$$ P^0_B = 500 Torr $$
Explanation
$$ x_AP^0_A + x_B P^0_B = 700 ......(i) $$
$$ X_A "P^0_A + X^"_B P^0_B = 0.30 P^0_A + 0.70 P^0_B = 600 .....(ii) $$
If moles of A ^b initially are C & Y then
$$ X = 0.75 \times \frac {2}{3} (x +y) + 0.30 \times \frac {1}{3}( x +y)......(iii) $$
$$ x_A = \frac {X}{x +y} \quad or \quad x_B = \frac {y}{x +y} ......(iv) $$
solving gives
$$X_A = 0.6 \quad x_B = 0.4 , P^0_A = \frac { 2500}{3} torr $$ & $$ P^0_B = 500 torr $$
The reading of pressure gauge at which only liquid phase exists
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499
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399
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299
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none
Explanation
$$ X_A = \dfrac34=0.75; \quad X_B = 0.25 $$
$$ P_{\text{bubble point}} = X_A P^0_A + X_B P^0_B $$
$$ P_{\text{bubble point}} = X_A P^0_A + X_B P^0_B $$
$$ 0.75 +400 + 0.25 \times 800 = 500 mm $$
Above 500 mm Hg only liquid phase exists.
$$ y_A = 0.75; \quad \quad y_B = 0.5 $$
At dew point:
$$ \dfrac {1}{P_T } = \dfrac {Y_A }{P^0A} + \dfrac {Y_B}{P^0_B } \Rightarrow \dfrac {1}{ P_T} = \dfrac { 0.75}{400} + \dfrac { 0.25}{800} = \dfrac { 1.5 + 0.25}{800} $$
$$ \Rightarrow P_T = \dfrac {800}{1.75} = 457.14\ mm Hg $$
Below the dew point, only the vapour phase exists.
Vapour pressure of a solution is
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Directly proportional to the mole fraction of the solvent
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Inversely proportional to the mole fraction of the solute
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Inversely proportional to the mole fraction of the solvent
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Directly proportional to the mole fraction of the solute
Explanation
For solutions containing non - volatile solutes , the Raoult's law may be stated as at a given temperature, the vapour pressure of a solution containing non - volatile solute is directly proportional to the mole fraction of the solvent.
Which of the following solution in water possesses the lowest vapour pressure?
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$$0.1 (M) NaCl$$
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$$0.1 (M) BaCl_2$$
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$$0.1 (M) KCl$$
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None of these
Explanation
The molarity for all the options is same i.e. 0.1 M, thus the deciding factor would be 'i'
in A, i = 2
in B, i = 3
in C, i = 2
This implies that dissociation into ions is maximum in the case of B, and thus least vapour pressure is observed
To which of the following gaseous mixtures is Dalton's law not applicable?
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$$Ne + He + SO_{2}$$
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$$NH_{3} + HCl + HBr$$
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$$O_{2} + N_{2} + CO_{2}$$
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$$N_{2} + H_{2} + O_{2}$$
Explanation
$$NH_{3}$$ and $$HCl$$ & $$HBr$$ is a reacting gas mixture to produce $$NH_{4}Cl$$ & $$NH_{4}Br$$.
Therefore, Dalton's law is not applicable.
$$60 \,gm$$ of Urea (Mol. wt 60) was dissolved in $$9.9$$ moles of water. If the vapour pressure of pure water is $$P_0$$ , the vapour pressure of solution is
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$$0.10 \,P_0$$
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$$1.10 \,P_0$$
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$$0.90 \,P_0$$
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$$0.99 \,P_0$$
Explanation
Given that,
Moles of water. $$N=9.9$$ moles
Moles of urea, $$n=\dfrac{w}{M}=\dfrac{60}{60}=1$$
Now,
$$\dfrac {P^{0} - P_{S}}{P^{0}} = \dfrac {n}{N} \Rightarrow \dfrac {P^{0} - P_{S}}{P^{0}} = \dfrac {1}{9.9} \Rightarrow 9.9 \,P^{0} - 9.9 \,P_s = P^{0}$$
$$\Rightarrow 8.9 \,P^{0} = 9.9 \,P_s \Rightarrow P_s = \dfrac {8.9}{9.9} P^{0} \approx 0.90 \,P^{0}$$
The vapour pressure lowering caused by the addition of $$100 \,g$$ of sucrose (molecular mass = 342) to $$1000 \,g$$ of water if the vapour pressure of pure water at $$25 ^\circ C$$ is $$23.8 \,mm \,Hg$$
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$$1.25 \,mm \,Hg$$
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$$0.125 \,mm \,Hg$$
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$$1.15 \,mm \,Hg$$
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$$00.12 \,mm \,Hg$$
Explanation
Given molecular mass of sucrose $$= 342$$
Moles of sucrose $$= \dfrac {100}{342} = 0.292 \,mole$$
Moles of water $$N = \dfrac {1000}{18} = 55.5 \,moles $$ and
Vapour pressure of pure water $$P^{0} = 23.8 \,mm \,Hg$$
According to Raoult's law
$$\dfrac {\Delta P}{P^{0}} = \dfrac {n}{n + N} \Rightarrow \dfrac {\Delta P}{23.8} = \dfrac {0.292}{0.292 + 55.5}$$
$$\Delta P = \dfrac {23.8 \times 0.292}{55.792} = 0.125 \,mm \,Hg$$
The pressure P of a gas is plotted against its absolute temperature $$T$$ for two different constant volumes, $$V_{1}$$ and $$V_{2}$$. when $$V_{1}$$ > $$V_{2}$$, the:
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Curves have the same slope and do not intersect
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Curves must intersect at some point other than $$T = 0$$
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Curve for $$V_{2}$$ has a greater slope than that for $$V_{1}$$
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Curve for $$V_{1}$$ has a greater slope than that for $$V_{2}$$
Explanation
At constant volumes $$P \alpha T$$
$$P=$$ constant $$T; PV = nRT \because P= \dfrac {nR} {V} T$$
slope $$= m = \dfrac{nR}{V} \because V_{2} < V_{1}$$
$$\dfrac{m_{1}} {m_{2}} = \dfrac{V_{2}} {V_{1}} \because m_{1} < m_{2}$$ is curve for $$V.$$ has a greater slope than for $$V.$$
Which has maximum vapour pressure?
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$$HI$$
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$$HBr$$
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$$HCl$$
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$$HF$$
Explanation
The lower is boiling point more is the vapour pressure. Boiling point order is $$HCl < HBr < HI < HF$$
Correct gas equation is:
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$$\dfrac {V_{1} T_{2}}{P_{1} }= \dfrac {V_{2} T_{1}}{P_{2}}$$
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$$\dfrac {P_{1} V_{1}}{P_{2}V_{2} }= \dfrac {T_{1}} {T_{2}}$$
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$$\dfrac {P_{1} T_{2}}{V_{1} }= \dfrac {P_{2} V_{1}}{T_{2}}$$
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$$\dfrac {V_{1} V_{2}}{T_{1}T_{2} }= P_{1}P_{2}$$
Explanation
Ideal gas law equation:
$$PV = nRT$$
$$\dfrac {P_{1} V_{1}} {T_{1} }=\dfrac {P_{2}V_{2}}{T}$$
$$ \because$$ $$\dfrac{P_{1}V_{1}}{P_{2}V_{2}}=$$ $$\dfrac{T_{1}}{T_{2}}$$
Hence, option B is correct.
Two which of the following the Dalton's law of particle pressure is not applicable?
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$$H_2$$ and $$He$$
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$$NH_3$$ and $$HCl$$
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$$N_2$$ and $$H_2$$
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$$N_2$$ and $$O_2$$
Explanation
Dalton's law of partial pressure is applicable to non-reaction gases $$NH_3$$ and $$HCl$$ are reacting gases, so Dalton's law will not be applicable for them.
Choose the correct answer
The graph of $$PV$$ vs $$P$$ for a gas is:
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parabolic
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hyperbolic
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a straight line parallel to X-axis
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a straight line passing through origin
Explanation
Since temperature is kept constant
P
V
=
Constant
Straight line parallel to the X-axis.
Directions: In the following questions, a statement of assertion is followed by a statement of reason. Mark the correct choice:
Assertion: The vapour pressure of an aqueous solution is less than 1.013 bar at 373.15 K.
Reason: Vapour pressure of water is 1.013 bar at 373.15K.
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If both assertion and reason are true and reason is the correct explanation of assertion.
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If both assertion and reason are true but reason is not the correct explanation of assertion
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If assertion is true but reason is false.
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If both assertion and reason are false.
Which of the following hydrogen halide is most volatile ?
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$$HF$$
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$$HCl$$
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$$HBr$$
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$$HI$$
Explanation
Most volatile hydrogen halide is the one which has least boling point viz $$HCl.$$
Which of the following is not a colligative property?
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Vapour pressure
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Depression in f. pt.
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Elevation in b. pt.
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Osmotic pressure
Explanation
$$\text { Auswer:- (a) vapour pressure. }$$
Colligative properties are those properties of solutions that depend on the
ratio of number of solute particles to number of solvent particles in a solution.
There are 4 colligative properties:-
-vapour pressure Lowering
-osmotic pressure
-freezing point depression
-boiling point elevation
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