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Published on: 30/07/2018
From the chapter Solution, some of the important questions are covered in this question paper. The questions are covers from the book back and the previous year questions.
Download CBSE Class 12th Standard CBSE Chemistry question papers, sample papers, important questions, and previous year solved papers in PDF format. Get free study materials, NCERT solutions, and exam preparation resources for Class 12th Standard CBSE Chemistry
Questions + Answers key
Take MCQ Chemistry Test

1.
A 5 percent solution (by mass) of cane-sugar (M.W. 342) is isotonic with 0.877% solution of substance X. Find the molecular weight of X.
2.
45 g of ethylene glycol (C2H4O2) is mixed with 600 g of water. Calculate
(i) the freezing point depression and
(ii) the freezing point of the solution.
3.
Calculate of solubility of a gas at a particular pressure from the known solubility at some other pressure (at the same temperature).
4.
An aqueous solution of 3.12 g of BaCl2 in 250 g of water is found to boil at 100.0832oC. Calculate the degree of dissociation of BaCl2. [K b (H2O) = 0.52 K/m.]
5.
Calculate the temperature at which a solution containing 54 g of glucose, (C6H12O6), in 250 g of water will freeze. (Kf for water =1.86 K kg mol-1)
6.
Determine the amount of CaCl2 (i = 2.47) dissolved in 2.5 litre of water such that its osmotic pressure is 0.75 atm at 27oC.
7.
Write Vant's Hoff equation. Name the method commonly used measuring osmotic pressure.
8.
What will be the mole fraction of water in methanol solution containing equal number of moles of water and methanol?
9.
What is the van't Hoff factor for a compound which undergoes tetramerisation in an organic solvent ?
10.
When is the value of van't Hoff factor more than one ?
11.
What mass of NaCl (molar mass = 58.5 g mol -1) must be dissolved in 65 g of water to lower the freezing point by 7.5 oC? The freezing point depression constant, K f for water is 1.86 K kg mol-1 . Assume van't Hoff factor for NaCl is 1.87.
12.
Two liquids A and B on mixing produce a warm solution. Which type of deviation from Raoult's law does it show ?
13.
Arrange the following aqueous solutions, each of strength 0.1 M, in order of increasing freezing and boiling points. C2H5OH, Ba3(PO4)2, Na2SO4, KCl Li3PO4. Justify your answer.
14.
(a) When 2.56 g of sulphur was dissolved in 100 g of CS2, the freezing point lowered by 0.383 K. Calculate the formula of sulphur (SX). (Kf for CS2 = 3.83 K kg mol-1, Atomic mass of sulphur = 32 g mol-1).
(b) Blood cells are isotonic with 0.9 % sodium chloride solution. What happens if we place blood cells in a solution containing;
(i) 1.2 % sodium chloride solution?
(ii) 0.4% sodium chloride solution?
15.
(a) State the following:
(i) Henry's law about partial pressure of gas in a mixture.
(ii) Raoult's law in its general form in reference to solutions.
(b) A solution prepared by dissolving 8.95 mg of a gene fragment in 35.0 ML of water has an osmotic pressure of 0.335 torr at 25oC. Assuming gene fragment is non-electrolyte, determine its molar mass.
16.
If sodium sulphate is considered to be completely dissociated into cations and anions in aqueous solution, the change in freezing point of water \((\Delta { T }_{ f })\), when 0.01 mol of sodium sulphate is dissolved in 1 kg of water, is (Kf = 1.86 K kg mol-1).
0.0744K
0.0186K
0.0372K
0.0558K
17.
What is the osmotic pressure of a 0.0020 mol dm-3 sucrose (C12H22O11) solution at 20oC ? (Molar gas constant, R = 8.314 JK-1mol-1)
4870 Pa
4.87 Pa
0.00487 Pa
0.33 Pa
18.
An aqueous solution of methanol in water has vapour pressure
equal to that of water
equal to that of methanol
more than that of water
less than that of water
19.
200 mL of water is added to 500mL of 0.2 M solution. What is the molarity of the dilluted solution ?
0.5010 M
0.2897 M
0.7093 M
0.1428 M
20.
People taking a lot of salt develop swelling or puffiness of their tissues. This disease is called ............ .
21.
The shrinking of a plant or animal cell due to outflow of water is called ............. .
22.
If pressure greater than osmotic pressure is applied on the solution seperated from the solvent by a semipermeable membrane, the flow of solvent is from ................ to .............. . The process is called ............. .
23.
The relative lowering vapour pressure of a solvent at a given temperature due to dissolution of a non-volatile solute is equal to ............... of ................ in the solution.
24.
The solubility of a solute decreases with increase of temparature if dissolution is .............. .
1.
\({ \pi }_{ cane\ sugar }={ \pi }_{ X }\)
Therefore, ccane sugar=cX
(where c is molar concentration)
\(\frac { { W }_{ cane\ sugar } }{ { M }_{ cane\ sugar } } =\frac { { W }_{ X } }{ { M }_{ X } } \)
\(\frac { 5g }{ 342 \ g \ { mol }^{ -1 } } =\frac { 0.877 }{ { M }_{ X } } \)
\(\\ \Rightarrow { M }_{ X }=\frac { 0.877\times 342 }{ 5 } g\ { mol }^{ -1 }\)
\(\Rightarrow { M }_{ X }=59.9 \ or \ 60 \ g{ \ { mol }^{ -1 } }\)
2.
Depression in freezing point is related to the molality, therefore, the molality of the solution with respect to ethylene glycol \(=\frac{\text { moles of ethylene glycol }}{\text { mass of water in kilogram }}\)
\(\text {Moles of ethylene glycol }=\frac{45 \mathrm{~g}}{62 \mathrm{~g} \mathrm{~mol}^{-1}}=0.73 \mathrm{~mol}\)
\(\text {Mass of water in } \mathrm{kg}=\frac{600 \mathrm{~g}}{1000 \mathrm{~g} \mathrm{~kg}^{-1}}=0.6 \mathrm{~kg}\)
\(\text {Hence molality of ethylene glycol }=\frac{0.73 \mathrm{~mol}}{0.60 \mathrm{~kg}}=1.2 \mathrm{~mol} \mathrm{~kg}^{-1}\)
Therefore freezing point depression,
ÄTf = 1.86 K kg mol–1 x 1.2 mol kg–1 = 2.2 K
Freezing point of the aqueous solution = 273.15 K – 2.2 K = 270.95 K
3.
From Henry's law, m = Kp. If m1 is the solubility of a gas at pressure
P1 and m2 is its solubility at pressure P2'\({m_1\over m_2}={P_1\over P_2}\)
Thus, knowing m1 at P1- m2 at P2 can be calculated. The equation, m = KP also suggests that plot of pressure, P vs solubility m will be a straight line passing through the origin with slope = K. Greater the value of K, greater is the solubility.
4.
ΔTb = 100.0832 - 100.0 = 0.0832°C,
Kb = 0.52 K kg mol-1,
WA = 250 g, WB = 3.12 g,
MB = 137 + 71 = 208 9 mol-1
Now \(ΔT_b=iK_b\times{W_B\over M_B}\times{1000\over W_A}\)
⇒ \(0.0832 = i \times 0.52 \times{3.12\over4 6.489}\times{1000\over 250}\)
\(⇒ i={0.0832\times208\over 4\times3.12\times0.52}={17.30\over 6.489}=2.66\)
\(\alpha={i-1\over n-1}={2.66-1\over 3-1}={1.66\over 2}=0.83\)
Degree of dissociation (α) = 83%
5.
\(\triangle { T }_{ f }={ K }_{ f }\times m\)
\( \Rightarrow \triangle { T }_{ f }={ K }_{ f }\times \frac { { W }_{ B } }{ { M }_{ B } } \times \frac { 1000 }{ { W }_{ A } }\)
\( \Rightarrow \triangle { T }_{ f }=1.86\times \frac { 54 }{ 180 } \times \frac { 1000 }{ 250 } \)
\( \Rightarrow \triangle { T }_{ f }=1.86\times \frac { 3 }{ 10 } \times 4=\frac { 22.32 }{ 10 } \\ =2.232 \ K\)
\( Freezing \ point=273K-2.232\)
\( =270.768 \ K\)
\(or \ F.pt.=273.15 \ K-2.23 \ K=270.7 \ K\)
6.
\(\text { Using relation, } \pi=i C R T=i \frac{n}{V} R T\)
\(n=\frac{\pi V}{i R T}=\frac{0.75 \times 2 \cdot 5}{2 \cdot 47 \times 0 \cdot 0821 \times 300}=0.0308 \text { mole }\)
\( \text { Molar mass of } \mathrm{CaCl}_{2}=40+2 \times 35 \cdot 5=111 \mathrm{~g} \mathrm{~mol}^{-1} \)
\(\therefore \text { Amount of } \mathrm{CaCl}_{2} \text { dissolved }\)
\(=0.0308 \times 111=3.42 \mathrm{~g}\)
7.
Vant's Hoff equation is \(\pi V=c R T\) Berkley and Hartley method is commonly used for measuring osmotic pressure.
8.
\(x_{\text {water }}=\frac{\text { Moles of water }}{\text { Moles of water }+ \text { Moles of methanol }}\)
Now, moles of water = Moles of methanol = 1(say)
\(x_{\text {water }}=\frac{1}{1+1}=0.5\)
9.
\(4 A \longrightarrow A_4\)
1 mole of A after association gives \(\frac{1}{4}\) mole of A4. Hence, \(i=\frac{1}{4}=0.25\)
10.
i > 1 when the solute undergoes dissociation in the solution.
11.
8.199 g
12.
Warming up of the solution means that the process of mixing is exothermic, i.e., \(\Delta H_{ mixing }=-ve\). This implies that the solution shows a negative deviation.
13.
In C2H5OH, i = 1, because it is not an electrolyte.
In Ba3(PO4)2 i = 5; In Na2SO4, i = 3;
In KCI, i = 2; In Li3PO4, i = 4
Greater the value of i, greater will be ΔTb' and higher will be b.pt. of solution.C2HsOH, KCI, Na2SO4, Li3PO4 and Ba3(PO4)2 is the increasing order of b.pt. Greater the value of i, greater will be ΔTf lower will be freezing point of solution.Therefore, Ba3(PO4)2 Li3PO4, Na2SO4, KCI and C2H5OH is the increasing order of freezing point.
14.
\(\Delta { T }_{ f }=\frac { { K }_{ f }{ W }_{ b }\times 1000 }{ { M }_{ b }\times { W }_{ a } } \)
\(0.383=\left( \frac { 3.83\times 2.56 }{ M\times 100 } \right) \times 1000\)
M = 256
S \(\times \) x = 256
32 \(\times \) x = 256
x = 8
(b) (i) If we place blood cells in solution containing 1.2% sodium chloride solution, they shrink.
(ii) It we place blood cells in solution containing 0.4% sodium chloride solution, they swell.
15.
(a) (i) Henry's Law: It states the partial vapour pressure of gas in vapour phase is directly proportional to mole fraction of the gas in the solution.
p = KH.x
where KH is Henry's law constant, 'x' is mole fraction of gas in solution and p is partial vapour pressure of the gas in solution.
(ii) Raoult's Law for solution of non-volatile solute: The relative lowering of vapour pressure for a solution is equal to the mole fraction of solute when solvent alone is volatile.
\({p_A^0-p_A\over p_A^0}=x_B\)
where p0 is vapour pressure of pure component 'A', pA is vapour pressure of component 'A' in solution, xB is mole fraction of solute, PA0 - PA is lowering of vapour pressure and \(p_A^0-p_A\over p_A^0\) is relative lowering of vapour pressure.
(b) πV = nRT
\(\Rightarrow\ \pi V={W_B\over M_B}\times R \times T\)
\(\Rightarrow\ {0.335\over 760}\times{35\over 1000}={8.95\times10^{-3}\times0.0821\times 2988\over M_B}\)
\(\Rightarrow\ M_B={760 \times 1000 \times 8.95 \times 10-3 \times 0.0821\times 298\over 0.335\times35}\)
\(={166.416\times10^3\over11.725}=14.19\times10^3\)
= 1.419 x 104 g mol-1
16.
(d)
0.0558K
17.
\(\pi =CRT\\ C=0.002\quad mol\quad { dm }^{ -3 }=2\quad mol\quad { m }^{ -3 }\\ R={ 8.314JK }^{ -1 }{ mol }^{ -1 },T=293K\\ \pi =2\times 80314\times 293=4872\quad Pa\)
18.
Methanol being more volatile than water, the solution of methanol in water will have more vapour pressure than water (a case of positive deviation).
19.
(d)
0.1428 M
20.
( )
edema
21.
( )
plasmolysis or crenation
22.
( )
solution, solvent, reverse osmosis
23.
( )
mole fraction, solute
24.
( )
exothermic
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