Education

1. Let’s start the
session….

2. Expressing Concentration of Solutions
1. Mass per cent or Per cent by mass (w/w)
2. Mass Fraction
3. Molarity (M)
4. Mole Fraction
5. Molality (m)
6. Normality (N)
7. Parts per million (ppm)

3. Mass per cent of Per cent by
mass (w/w)
In case a solid dissoved in a liquid, the per cent by mass means the amount of
solute in grams dissolved in 100 grams of the solution

4. Ǫ. 1
A solution is prepared by adding 2 g of a substance A to 18 g of water.
Calculate the mass per cent of the solute

5. Mole Fraction
It is defined as the ratio of the number of moles of one component to the total
number of moles of the components present in the solution.
Mole fraction is generally denoted by symbol x.

6. Ǫ. 2
A solution contains 25% water, 25% ethanol and 50% acetic acid by mass.
Calculate the mole fraction of each component.

7. Molarity (M)
It is defined as the number of moles of the solute dissolved per litre or dm3 of
the solution.
Molarity is denoted by ‘M’
The solution may be called molar, semimolar, decimolar, centimolar or
millimolar, depending upon whether its molarity is 1, 0.5, 0.1, 0.01 or 0.001
respectively.
Molarity changes with change in temperature.
Moles of solute before dilution = Moles of solute after dilution.
M1V1 = M2V2

8. Molarity (M)

9. Ǫ. 3
Calculate the molarity of a sodium hydroxide solution which has been
prepared by dissolving 20 g of sodium hydroxide in one litre of solution.

10. Ǫ. 4
How many moles and how many gram of sodium chloride are present in
200 cm3 of 0.2 M NaCl slution ?

11. Molality (m)
The molality of a solution is defined as the number of moles of solute dissolved
per 1000 g or 1kg of the solvent. It is represented by ‘m’

13. Parts per million (ppm)
It is the number of parts of the component present per million parts of the
solution.

14. Ǫ. 1
A sample of drinking water was found to be severely contaminated with
chloroform, CHCl3, supposed to be carcinogen. The level of contamination
was 15 ppm (by mass)
(i) Express this in percent by mass.
(ii)_ Determine the molality of chloroform in the water sample.

15. Ǫ. 1
A sample of drinking water was found to be severely contaminated with
chloroform, CHCl3, supposed to be carcinogen. The level of contamination
was 15 ppm (by mass)
(i) Express this in percent by mass.
(ii)_ Determine the molality of chloroform in the water sample.

16. Ǫ. 2
Concentrated nitric acid used in the laboratory work in 68% nitric acid by
mass in aqueous solution. What should be the molarity of such a sample
of the acid if the density of solution is 1.5 g mL–1 ?

17. Calculate the molarity of a solution containing 40 g of NaOH dissolved in two litre of the
solution.
Ǫ. 3

18. The mole fraction of the solute in one molal aqueous solution is
(a) 0.027
(c) 0.018
(b) 0.036
(d) 0.009
Ǫ. 4

19. Solubility
● Solubility of a substance is its maximum amount that can dissolve
in specific amount of solvent under given set of conditions.

20. Effect of temperature
 For endothermic dissolution process, solubility increase with increase in
temperature.
 For exothermic dissolution process, solubility decrease with increase in
temperatre
Effect of Pressure
No significant effect since solids and liquids are highly incompressible and
practically remain unaffected by change in pressure.
Solubility ofsolids in liquids

21. Henry’s Law

22. Solubility of
gases in liquids
Effect of pressure- Henry’s Law - on solubility of gases in liquids
⇒the solubility of a gas at a given temperature is directly proportional
to the pressure at which it is dissolved.

24. Solubility of
gases in liquids
Effect of pressure- Henry’s Law - on solubility of gases in liquids
⇒the solubility of a gas at a given temperature is directly proportional
to the pressure at which it is dissolved.

25. Solubility of gases in liquids
Effect of pressure- Henry’s Law - on solubility of gases in liquids
⇒the solubility of a gas at a given temperature is directly proportional
to the pressure at which it is dissolved.

26. I. The units of Henry law constant are same as those of
pressure
II. Different gases have different values of Henry law constant.
Higher the value of KH of a gas is, lower will be its solubility and
vice versa.
CHARACTERISTICS OF HENRY LAW CONSTANT (KH)

27. Solubility of gases in liquids
Effect of pressure- Henry’s Law - on solubility of gases in liquids

28. I. Soft drinks, soda water and other carbonated beverages contains
dissolved carbon dioxide.
APPLICATIONS OF HENRY'S LAW

29. I. Anoxia - the low content of blood oxygen causes climbers to
become weak and reduces their thinking ability which are
symptoms of anoxia.
APPLICATIONS OF HENRY'S LAW

31. I. Bends - scuba divers suffer from the painful effects when they
come towards the surface
APPLICATIONS OF HENRY'S LAW

37. Numericals on Henry’s Law

38. Henry’s Law
(Practice)

39. 3
Numericals on Henry’s Law
2

40. 4
Numericals on Henry’s Law
2

42. 5
Numericals on Henry’s Law
2

43. I. The units of Henry law constant are same as those of
pressure
II. Different gases have different values of Henry law constant.
Higher the value of KH of a gas is, lower will be its solubility and
vice versa.
CHARACTERISTICS OF HENRY LAW CONSTANT (KH)

44. I. The pressure of the gas is not too high.
II. The temperature is not too low.
III. The gas should not undergo any chemical reaction with the
solvent.
IV. The gas should not undergo association or dissociation in
solution.
LIMITATIONS OF HENRY'S LAW

48. Calculation of molality of
the mole fraction is
given.
Calculation of mole
fraction of the molality is
given.

49. 02 is bubbled through water at 293 K Assuming that 02 exerts a partial
pressure of 0.95 bar. Calculate the solubility of 02 in moles per litre and
gL-1. The value of Henry law constant (KH) for 02 is 34.84 k bar.

50. Henry's law constant of CO2 in water is 1.67 x 108 Pa at 298 K. Calculate
the quantity of CO2 in 500 mL of soda water when packed under 2.5 atm
CO2 pressure at 298 K

51. If N2 gas is bubbled through water at 293 K, how many millimoles of N2
gas would dissolve in 1litre of water? Assume that N2 exerts a partial
pressure of 0.987 bar. Given that Henry's law constant for N2 at 293 K is
76.48 kbar.

52. The value of Henry's law constant-for some gases at 293 K is given
below. Arrange the gases in the increasing order o f their solubility
He : 144 .97 kbar, H2 : 69.16 kbar, N2 : 76.48 kbar, 02 : 34.86 kbar
A. He < N2 < H2 < 02
B. 02 < H2 < N2 < He
C. H2 < N2 < 02 < He
D. He < 02 < N2 < H2

53. The value of Henry's law constant-for some gases at 293 K is given
below. Arrange the gases in the increasing order o f their solubility
He : 144 .97 kbar, H2 : 69.16 kbar, N2 : 76.48 kbar, 02 : 34.86 kbar
A. He < N2 < H2 < 02
B. 02 < H2 < N2 < He
C. H2 < N2 < 02 < He
D. He < 02 < N2 < H2

54. At high altitudes the partial pressure of oxygen is less than that at the
ground level:This leads to
A. Low concentrations of oxygen in the blood and tissues
B. High concentrations of oxygen in the blood and tissues
C. Release of dissolved gases and formation of bubbles of nitrogen in
the blood
D. Thickening of blood and tissues.

55. At high altitudes the partial pressure of oxygen is less than that at the
ground level:This leads to
A. Low concentrations of oxygen in the blood and tissues
B. High concentrations of oxygen in the blood and tissues
C. Release of dissolved gases and formation of bubbles of nitrogen in
the blood
D. Thickening of blood and tissues.

56. What is the molarity of a solution containing 10 g of NaOH in 500 mL of
solution ?
(a) 0.25 mol L–1 (b) 0.75 mol L–1 (c) 0.5 mol L–1 (d) 1.25 mol L–1

57. The value of Henry’s constant KH is-------------------------------
(a) Greater for gases with higher solubility
(b) Greater for gases with lower solubility
(c) Constant for all gases
(d) Not related to the solubility of gases

58. The value of Henry’s constant KH is-------------------------------
(a) Greater for gases with higher solubility
(b) Greater for gases with lower solubility
(c) Constant for all gases
(d) Not related to the solubility of gases

59. Calculate the molality of ethanol solution in which the mole fraction of
water is 0.88
[A] [CBSE SQP 2018-19]

60. Calculate the mole fraction of benzene in solution containing 30% by
mass in carbon tetrachloride.
[A][NCERT Exemplar]