HOME ASSIGNMENT FOR SUMMER VACATION CLASS- XII
By- A P SINGH ,PGT –CHEM.
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1.1. What is meant by ‘reverse osmosis’?
(CBSE 2011,09)
1.2. Explain how molarity value of a solution can be converted into its
molality ? (CBSE/FN 2011)
1.3. What is the advantage of using osmotic pressure as compared to other
colligative properties for determination of molar mass of a solute in
solution ?(CBSE 2010)
2.1. Define the following terms :(1 X 5)
(i) Mole fraction (CBSE 2012,09) (ii) Ideal solutions(CBSE 2012)
(iii) molality of a solution (2009)(iv) Colligative properties (2009)
(v) van’t Hoff factor (2009)
2.2. Explain the following :(CBSE 2012,13)
(i) Henry’s law about dissolution of a gas in a liquid
(ii) Boiling point elevation constant for a solvent
2.3.Non-ideal solutions exhibit either positive or negative deviations from
Raoult’s law. What are these deviations andwhy are they caused?
Explain with one example for each type.(CBSE 2010)
2.4 Differentiate between molarity and molality for a solution. How does a
change in temperature influence their values ?
(CBSE 2011,10,09)
Define the term osmosis and osmotic pressure. Is the osmotic pressure of
asolution a colligative property ? Explain (CBSE 2011)
2.6. State the following :- (CBSE 2011)
(i) Henry’s law about partial pressure of a gas in mixture.
(ii) Raoult;s law in its general form in reference to solutions.
2.7. A 0.561 m solution of an unknown electrolyte depresses the freezing
pointpf water by 2.93o C. What is van’t Hoff Factor for this electrolyte ?
The freezing point depression constant (Kf) for water is1.86 K kg mol-1 .
3.1.15.0 g of an unknown molecular material is dissolved in 450 g of water.
The resulting solution freezes at ─0.340 C. What is the molar mass of
the material ? (Kffor water = 1.86 Kkgmol−1).
(CBSE 2012,10)
3.2 A solution of glycerol (C3H8O3) in water was prepared by dissolving some
glycerol in 500 g of water. This solution has a boiling point of 100.420C.
what mass of Glycerol was dissolved to make this solution ?
Kb for water = 0.512
(CBSE 2012,10)
3.3. A solution prepared by dissolving 1.25 g of oil of winter green
(methyl salicylate) in 99.0 g of benzene has aboiling point of 80.31 °C.
Determine the molar mass of this compound.
(B.P. of pure benzene = 80.10 °C and Kb forbenzene = 2.53 °C kg mol−1).
(CBSE 2010)
3.4 Calculate the boiling point of an aqueous solution prepared by adding 15 g
Of NaCl to 250.00 g of water . (Kb for water = 0.512 kg mol-1 , Molar Mass
Of NaCl = 58.44 gmol-1 )(CBSE 2011)
3.5. Calculate the freezing point of an aqueous solutioncontaining 10.50 g of
MgBr2in 200 g of water . (molar mass of MgBr2 = 184g/mol and for water
K f = 1.86 K kg mol-1)(CBSE 2011)
3.6. 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 the gene
fragment is a non-electrolyte , determine its molar mass.
(CBSE2011)
3.7. What would be the molar mass of a compound if 6.21 g of it dissolved in 24.0 g
of chloroform form a solution that has a boiling point of 68.04O C. The boiling
point of pure chloroform is 61.7o C and boiling point elevation constant, Kb for
chloroform is3.63OC. (CBSE 2011)
2.5.
3.8. What mass of NaCl must be dissolvedin 65.0 g of water to lower the freezing
point of water by 7.5o C ? The freezing point depression constant (Kf) for
water is 1.86 C/m. Assume van’t Hoff factor for NaCl is 1.87 .
(molar mass of NaCl = 58.5 g/mol).
(CBSE 2011,10)
3.9. What mass of ethylene glycol (molar mass = 62.0 g/mol) must be added to 5.5
kg of water to lower the freezing point of water from 0o Cto -10.0O C?Kf for
water = 1.86 K kg mol-1 . (CBSE 2010)
3.10. 100 mg of a protein was dissolved in just enough water to make 10.0 mL of
solution .If this solution has an osmotic pressure of 13.3 mm Hg at 25OC ,
what is the molar mass of protein ? (R = 0.0821 Latm K-1mol-1)(CBSE 2009)
3.11.Calculate the freezing point depression expected for 0.0711 m aqueous of
Na2SO4 .If this solution actually freezes at-0.320 oC, what would be the value
of van’ t Hoff factor ?Kf for water = 1.86 K kg mol-1(CBSE 2009)
3.12. What concentration of nitrogen should be present in a glass of water at room
temperature ? Assume a temperature of 25OC, a total pressure of 1 atm
and mole fraction of nitrogen in air of 0.78
[ KH for nitrogen = 8.42 x 10 ─7M/mm Hg.]
(CBSE 2009)
HOTS QUESTIONS
1. A 500 gm of toothpaste sample has 0.2 g of fluoride concentration. What is the
concentration of fluoride in terms of ppm level?
2. Aquatic species are more comfortable in cold waters rather than in warm
water. GiveReason.
3. A) Why the vapour pressure of a solution of glucose in water lower than that of
water?
B) 0.1 molal solution of glucose and NaCl respectively. Which one will have
higher boiling point?
4. H2S, a toxic gas with rotten egg like smell is used for qualitative analysis. If the
solubility of H2S in water at STP is 0.195 m, calculate Henry’s law constant
(kH=282 bar).
5. The elements A and B form purely covalent compounds having molecular
formulae AB2 and AB4. When dissolved in 20g of benzene, 1g of AB2 lowers
the freezing point by 2.3K, whereas 1g of AB4 lowers it by 1.3K. themolal
depression constant for benzene is 5.1 K kg/mol, calculate the atomic mass of
A and atomic mass of B.
6. To 500 cm3 of water 3.0 X 10-3 kg of acetic acid is added. If 23% of acetic acid
is dissociated, what will be the depression in freezing point? Kf and density of
water are 1.86 K kg mol-1 & 0.997 g cm-3respectively
VALUE BASED QUESTIONS
1. Scuba divers when come towards the surface, the pressure gradually decreases
resulting in the released of dissolved gases leading to formation of bubbles of
nitrogen gas in the blood which blocks the capillaries and thus harmful kinds
are created. To avoid bends and toxic effects of high concn of nitrogen gas,
the air is diluted with helium. After reading the above passage, answer the
following questions.
i) Why is the harmful condition of bends overcome by the use of helium.
ii) Which law is used to calculate the concentration of gases in solution.
iii) Mention the value associated with providing divers air diluted with helium.
2. Ram takes a open pan to cook vegetables at a hill station while shyam cook
the same vegetables in a pressure cooker at the same place.
(a) Explain with reason who will cook vegetable faster.
(b) Mention the reason for the delay in cooking.
(c) Which value is learnt by the student in the process of cooking food in the
pressure cooker.