solution question and answers 2012 (1).docx

8/14/2019 solution question and answers 2012 (1).docx

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SOLUTIONS

1. What is molarity?It is the number of moles of solute present in IL of solution.

2. What is molality?It is the number of moles of solute present in 1 kg of solvent.

3. Which concentration term remain unchanged by temperature?Molality

4. Why does the molality of solution remain unchanged with temperature?Because mass of solute and solvent are independent of temperature.

5. How does molarity of solution change with temperature?With rise in temperature molarity decreases because of volume of solution increases.

6. What is mole fraction?It is the ratio of number of moles of one component and total number of moles of solution.

7. Differentiate between molarity and molality.a) Molarity is the number of moles of solute present in IL of solution. Molality is the

number of moles of solute present in 1 kg of solvent.

b) Molarity decreases with increase in temperature but molality is independent oftemperature.

8. State Henrys law. Give two applications.The partial pressure of a gas in vapour phase (p) is directly proportional to the mole fraction

of the gas (x) in the solution,

i.e., p = KHx

Applications of Henrys law

(i) Bottles are sealed under high pressure to increase the solubility of CO2 in soft drinksand soda water.

(ii) the oxygen tanks used by scuba divers are filled with air and diluted with helium toavoid bends.

9. Define vapour pressure. What happens to the vapour pressure when non-volatile solutedissolves in the liquid?

The pressure exerted by vapour molecules on the surface of its liquid at equilibrium.


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Vapour pressure decreases when non-volatile solute is added to it.

10.State Raoults law for solutions containing volatile liquidsFor a solution of volatile liquids, the partial vapour pressure of each component in the

solution is directly proportional to its mole fraction.

11.What is ideal solution? Give graphical representation.Solutions which obey Raoults law over the entire range of concentrations

An ideal solution will be formed when intermolecular forces of attraction between themolecules of solute (A A) and those between the molecules of solvent (B B) are nearly

equal to those between solute and solvent molecules (A B).

For ideal solution: Enthalpy of mixing ,mix H = 0Volume of mixing, mix V = 0

Examples: n-Hexane and n-heptane, bromoethane and chloroethane, benzene and toluene


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12.What is non-ideal solution?

Solutions which do not obey Raoults law over the entire range of concentration

The vapour pressure of a non-ideal solution is either higher or lower than that

predicted by Raoults law.

o Positive deviation from Raoults law When vapour pressure is higher

o Negative deviation from Raoults law When vapour pressure is lower

13. With suitable diagram and appropriate examples explain a non-idealsolutionwith positive

deviation.

The intermolecular forces of attraction between solute-solvent molecules are weaker than those

between solute-solute molecules and solvent-solvent molecules. Therefore, solvent molecules can

easily escape, resulting in increase in vapour pressure.

o Example: Ethanol and acetone mixture13.What are the sign of H and V for solution with positive deviation?

H =+ve V = + ve

14. With suitable diagram and appropriate examples explain a non-ideal solution with

negative deviation.

The intermolecular forces of attraction between solute-solute molecules and solvent-solvent

molecules are weaker than those between solute-solvent molecules. This results in the decreasing of


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vapour pressure.

o Example Chloroform and acetone mixtureThe intermolecular attractive forces between solute-solvent molecules increase due tothe formation of H-bond.

15.What are the sign of H and V for solution with negative deviation?

H = -ve V = - ve

16.What type of solution is formed when chloroform is mixed with acetone?

Solution with negative deviation

17. What type of solution is formed when ethanol is mixed with water?

Non-ideal solution with positive deviation.

18. Give an example of solution showing positive deviation from ideal behaviour.

Ethanol and hexane

19. Give an example of solution showing negative deviation from ideal behaviour.

Water and nitric acid.


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20. Define azeotropic mixture.

A mixture of liquids which boil at constant temperature without change in composition is called

azeotropic mixture.

21. What are maximum boiling azeotropes? Give an example.

A mixture of liquids which boils at a temperature higher than the boiling point of both the components

in pure state.

Example: Hydrochloric acid and water

Non-ideal solution showing negative deviation forms maximum boiling azeotropes

22. What are minimum boiling azeotropes? Give an example.

A mixture of liquids which boils at a temperature lower than the boiling point of both the components

in pure state.

Example: ethanol and water

Non-ideal solution showing positive deviation forms minimum boiling azeotropes.

23. What type of behavior is expected when water is added to sulphuric acid?

Negative deviation.

24.What are colligate properties? Give examples.

Those properties which depend upon number of solute particles only and not on nature of solute arecalled colligative properties.

1. Relative lowering of vapour pressure2. Elevation of boiling point.3. Depression of freezing point.4. Osmotic pressure.

25. Define boiling point.

The temperature at which vapour pressure of liquid becomes equal to atmospheric pressure.

26. Illustrate elevation in boiling point with help of a diagram.

With addition of non-volatile solute, vapour pressure decreases and hence, boiling point increases.

When a non-volatile Solute is dissolved in a solvent its vapour pressure decreases.Hence vapour

pressure of solution becomes equal to atmospheric pressure only at higher temperature.


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Here, = Elevation of boiling point Where,

Tb= Boiling of solution

= Boiling point of solvent

27. Derive the expression for elevation in boiling point.

Tbm(for dilute solution)Tb= Kbm

Where, m= Molality

Kb= Proportionality constant known as Boiling Point Elevation Constant or Molal Elevation

Constant or Ebullioscopic constant (Unit = K kg mol1

)

Where,w2= Mass of solute M2= Molar mass of solute w1= Mass of solvent

28.Write an expression for calculating molar mass of solute from elevation in boiling point.

29. Illustrate depression in freezing point with help of a diagram.

With addition of non-volatile solute, vapour pressure decreases, which leads to a decrease in freezing

point.


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When a non-volatile solute is dissolved in a solvent its vapour pressure decreases.Hence vapour

pressure of solvent and solution becomes equal at lower temperature.

Here, = Depression of freezing pointWhere,

= Freezing point of solvent Tf= Freezing point of solution

30.Derive an expression for depression in freezing point.

For dilute solution (ideal solution),Tfm

Tf= Kfm

Where,

m = Molality Kf= Proportionality constant known as Freezing Point Constant or Molal

Depression Constant or Cryoscopic constant (Unit = K kg mol1)

Where,

w2= Mass of solute M2= Molar mass of solute w1= Mass of solvent

31. Write an expression for calculating molar mass of solute from depression in freezing point .

32. What is an antifreeze?


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It is a liquid which is added to another liquid to prevent its freezing .Eg: Ethylene glycol in water

33. Why does the boiling point of solution increase on adding non-volatile solute?

On adding nonvolatile solute to liquid its vapour pressure decreases. Hence boiling point increases

34. Why does the freezing point of solution decrease on adding non-volatile solute?

On adding nonvolatile solute to liquid its vapour pressure decreases. Hence freezing point decreases.

35. Define ebullioscopic constant.

It is the elevations in boiling point when I mol of solute is added to 1000g of solvent.

36. Define Cryoscopic constant.

It is the depression in freezing point when 1 mol of solute is added to 1000g of solvent.

37. What is osmosis ?

The process of flow of solvent from pure solvent to solution or from less concentrated solution to

more concentrated solution through a semi permeable membrane is called osmosis.

38. Define osmotic pressure.

The extra pressure applied on the solution side to just stop the process of osmosis, when the solvent

and solution are separated by semipermeable membrane is called osmotic pressure.

39. Osmotic pressure is a colligative property. Why?

Osmotic pressure is a colligative property because it depends only on number of solute particles and

not depend on the nature of solute particles.

40. Write different expressions for Osmotic pressure.

1. v= n2RT

= Osmotic pressure V= volume of solution in Litre

n2= number of moles of solute R = gas constant T = Temperature in Kelvin

2. w2=MassofsoluteM2 = Molar mass of solute


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3. = MRT OR = CRT M = Molarity of solution C = concentration of

solution

41.Write the formula to find molar mass of solute from osmotic pressure.

42. What is the advantage of osmotic pressure method for determining molecular mass of

solute?

a) This method is performed at room temperature

b) Osmotic pressure method gives large value even for dilute solution

43. State how does osmotic pressure vary with temperature.

Osmotic pressure increases with increase in temperature

44.What is reverse osmosis? What is the use of reverse osmosis?

If the pressure applied on the solution is greater than its osmotic pressure, then the direction of

osmosis is reversed i.e., the solvent starts passing from solution to solvent. The phenomenon is called

reverse osmosis.

This phenomenon is used in purification (desalination) of sea water.

45. What are isotonic solutions?

Solutions having same osmotic pressure are called isotonic solutions

46. Define i) hypertonic solution ii) hypotonic Solution

i) Solution having higher osmotic pressure is called hypertonic solution.

ii) Solution having lower Osmotic pressure is called hypotonic Solution.


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47. Doctors advise gargles by saline water in case of sore throat. Why?

Saline water is hypertonic solution therefore fluids responsible for irritation in throat will come out.

48. What is the statement of Raoultslaw for solution containing non-volatile solute?

Relative lowering of vapour pressure is equal to the mole fraction of the solute.

i.e.,

Where,

= Vapour pressure of the solvent

p1= Vapour pressure of the solution

x2= Mole fraction of the solute

However,

Where, n2= Number of moles of solute

n1= Number of moles of solvent

49.What is the formula to find vapour pressure of solution if solute is non-volatile?

50.What is the formula to find Molar mass and weight of non-volatile solute if vapour pressure

of solution is given?

Where,

w2= Mass of solute

M2 = Molar mass of solute

w1= Mass of solvent

M1= Molar mass of solvent

51.What is the formula to find i) vapour pressure of solution ii) composition (mole fractions) ofcomponents if both the components are volatile liquids?


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52. What is the formula to find composition (mole fractions) of components in vapour phase?

y1, y2 = Mole fractions of the components 1 and 2 respectively in the vapour phase

53.What is abnormal molarmass?

Due to association or dissociation of solute, the molar mass of a solutecalculated from its

colligative property is either lower or higher than the expected or normal value. Such molar mass

is called abnormal molar mass.

Dissociation:

KCl K ++ Cl

Association:

2CH3COOH (CH3COOH)2

54.What is vant Hoffs factor?

The ratio of normal molar mass and abnormal molar mass is called van t Hoffs factor

OR

The ratio of observed colligating properties and norm colligative properties is called vant Hoffs

factor


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55.What is thevalueof vant Hoffs factor if solute particles undergo dissociation?

More than one

56. What is the value of vant Hoffs factor if solute particles undergo association ?

Less than one

57. What is the value of vant Hoffs factor if solute particles do not undergo association and

dissociation?

One

58. Name the colligative property mostly used for the determination of molecular mass of

solute.

Osmotic pressure because this method used at room temperature and macromolecules decomposeat higher temperature.

59. Give examples for solute which undergo association.

Acetic acid in benzene, benzoic acid in benzene

60. Give examples for solutes which undergo dissociation.

Electrolytes(NaCl,KCl,Na2SO4,K2SO4)

61. Give modified equations for colligative properties

Relative lowering of vapour pressure of solvent,

*Elevation of boiling point, Tb= iKbm

*Depression of freezing point, Tf= iKfm


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*Osmotic pressure of solution, = in2RT/V

62.What is the formula to find vant Hoffs factor if dissociation is not complete?

= i-1/n-1

= degree of dissociation n = number of particles after dissociation

eg:KClK++ Cl

n =2

63. What is the formula to find vant Hoffs factor if solute particles undergo association?

=i- 1/ 1/n-1

For dimer n=2

64. What is the value of vant Hoffs factor for NaCl?

2

65. What is the value ofvant Hoffs factor for Na2SO4 ?

3

66. What is the value of vant Hoffs factor for solute which undergoes dimerization?

67. What is the value ofvant Hoffs factor for solute which undergoes tetramerisation ?

68. Which will have greater boiling point? (i) 1M urcasolution (ii) 1M NaCl solution

1M NaCl solution because number of particles are more

69.Which will have greater freezing point? (i) 1M urcasolution (ii) 1M NaCl solution

1M urea solution because number of particles are less

70. Why a mixture of liquids shows negative deviation from ideal behavior?


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Because intermolecular force of attraction between two liquids is stronger than that between pure

liquids.

71. Why a mixture of liquids shows positive deviation from ideal behavior?

Because intermolecular force of attraction between two liquids is weaker than that between pure

liquids.

72. Osmotic pressure of 1M KCl solution is higher than 1M urea solution. Why?

KCl is an electrolyte, it undergoes dissociation insolution,hence number of particles increases.

Urea is non-electrolyte.

solution question and answers 2012 (1).docx

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