SOLUTION
INTRODUCTION
Solutions are an important part of Class 12 Chemistry and play a key role in both board exams and competitive exams. In this chapter, we study what solutions are, their different types, and how to express their concentration using terms like molarity (M), molality (m), normality (N), and percentage methods.
Understanding these concepts helps in solving numerical problems easily and builds a strong foundation for topics like colligative properties and chemical equilibrium. This post will explain everything in a simple and easy way along with important numericals.
SOLUTION
A solution is a homogeneous mixture of two or more chemically non- reacting substances whose composition can be varied within certain limits.
In a homogeneous mixture , all the particles are of molecular size, i.e., up to nanometre in diameter and the different constituents of the mixture cannot be separated by any of the physical methods like filtration, settling or centrifuging. Every solution is made up of a solvent and one or more solutes.
BINARY SOLUTION
A solution containing only one solute dissolved in a solvent is called binary solution.
SOLVENT AND SOLUTE
A solvent is that component of the solution which is present in larger amount by mass than the other component, called as solute.
AQUEOUS AND NON- AQUEOUS SOLUTION
Solutions in water are called aqueous solutions.
The solutions in which water is not the solvent are called non - aqueous solutions. Benzene , ether, carbon tetrachloride etc., are used as solvents in non aqueous solutions.
TYPES OF SOLUTIONS ON THE BASIS OF PHYSICAL STATE OF THE SOLVENT
| S.No. | Solute | Solvent | Type of solutions | Examples |
|---|---|---|---|---|
| 1. | Solid | Solid | Solid in solid | Alloys(brass, bronze, 22 carat gold etc.) |
| 2. | Liquid | Solid | Liquid in Solid | Hydrated salts, Amalgam of Hg with Na |
| 3. | Gas | Solid | Gas in Solid | Dissolved gases in minerals or H2 in Pd |
| 4. | Solid | Liquid | Solid in liquid | Salts/glucose/sugar/urea solution in water |
| 5. | Liquid | Liquid | Liquid in liquid | Methanol/Ethanol in water |
| 6. | Gas | Liquid | Gas in liquid | Aerated drinks, Oxygen in water |
| 7. | Solid | Gas | Solid in gas | Iodine vapours in air, Camphor in N2 gas |
| 8. | Liquid | Gas | Liquid in gas | Humidity in air, Chloroform in N2 gas |
| 9. | Gas | Gas | gas in gas | Air ( N2 gas + O2 gas ) |
EXPRESSING CONCENTRATION OF SOLUTIONS
(A) PERCENTAGE
The percentage of a solution is usually expressed either as ' percentage by mass' or ' percentage by volume' or ' mass by volume'
When nothing is mentioned, it stands for percentage by mass.
cm³ (cc) and mL are taken as equivalent and can be used without any distinction.
In case of a solid dissolved in a liquid
The percentage by mass means the mass of the solute in grams present in 100 g of the solution,i.e.,it is weight/ weight (w/w).
Example: 10% solution of sodium carbonate by mass means 10 g of sodium carbonate are present in 100 g of the solution.
The percentage by volume means the mass of the solute dissolved in 100 cm³ or 100 mL of the solution, i.e., it is weight/volume (w/v).
Example : 10% solution of sodium carbonate by volume means 10 g of sodium carbonate dissolved in 100 cm³ or 100 mL of the solution.
In case of a liquid dissolved in another liquid
The percentage by mass means the mass of the solute in grams present in 100 g of the solution,i.e.,it is weight/ weight (w/w).
Example: 10% solution of ethyl alcohol by mass means 10 g of ethyl alcohol are present in 100 g of the solution (i.e., 90 g of water).
The percentage by volume means the volume of the solute in cm³dissolved in 100 cm³ or 100 mL of the solution, i.e., it is volume/volume (v/v).
Example : 10% solution of ethyl alcohol by volume means 10 cm³ of ethyl alcohol are dissolved in 100 cm³ or 100 mL of the solution (90 cm³ of water).
(B) STRENGTH
The amount of the solute in gram present in one litre ( or decimetre cube) of the solution is called strength of the solution.
It is expressed in g/litre (or g/dm³)and is usually written as gL⁻¹
(C) MOLARITY ( M )
The number of moles of the solute dissolved per litre of solution is called molarity.
unit - mole / litre
Molarity is temperature dependent.
Some common fractions of molarity
1M = Molar
M/2 = Semimolar
M/10 = Decimolar
M/100 = Centimolar
M/1000=Millimolar
(D) FORMALITY (F)
The number of gram formula masses of the solute dissolved per litre of the solution is called formality.
It is used for ionic compounds
.
(E) NORMALITY (N)
The number of gram equivalents of the solute dissolved per litre (dm³) of given solution is called Normality (N) of the solution.
(F) MOLALITY (m)
The number of moles of the solute dissolved in 1 kg of the solvent.
Its unit is mol/kg
Molality is temperature independent.
(G) MOLE FRACTION (x)
Mole fraction of a constituent (solute or solvent) is the fraction obtained by dividing number of moles of that constituent by the total number of moles of all the constituents present in the solution.
or,Mole fraction of a component is the moles of the component divided by the total moles of all components in the solution
Mole fraction has no unit. It is a dimensionless quantity.
The sum of mole fractions of all the constituents of a solution is always equal to unity.
(H) Parts Per Million (ppm)
The mass of the solute present in one million (10⁶) parts by mass of the solution is called ppm of the solution.
or,The volume of the solute present in one million (10⁶) parts by volume of the solution is called ppm of the solution.
For very dilute solution ,i.e., when a very small quantity of a solute is present in a large quantity of a solution, the concentration of the solute is expressed in terms of ppm.
For a solute A, in terms of mass,
And in terms of volume,
The pollution of the atmosphere is reported in ppm but expressed in terms of volumes rather than masses,i.e., the volume of the harmful gas in cm³ present in 10⁶ cm³ of the air.
MCQ
Types of Solutions
1. Which of the following is a solid solution?
A. Air
B. Brass
C. Salt in water
D. Sugar in water
2. Air is an example of:
A. Solid in gas
B. Gas in gas
C. Liquid in gas
D. Gas in liquid
3. Which is a liquid-liquid solution?
A. Ethanol + Water
B. Hydrogen + Oxygen
C. Salt + Water
D. Copper + Zinc
4. Alloy is an example of:
A. Gas solution
B. Liquid solution
C. Solid solution
D. Colloid
5. Which is gas in liquid solution?
A. Oxygen in water
B. Sugar in water
C. Nitrogen in air
D. Brass
Concentration Terms
6. Molarity depends on:
A. Temperature
B. Pressure
C. Volume
D. Mass
7. Molality is defined as:
A. Moles of solute per litre
B. Moles of solute per kg solvent
C. Grams per litre
D. Mass percent
8. Which concentration term is temperature independent?
A. Molarity
B. Molarity & Normality
C. Molality
D. Mole fraction
9. Mole fraction is:
A. Ratio of moles of solute to total moles
B. Ratio of mass
C. Ratio of volume
D. Ratio of density
10. Normality is based on:
A. Equivalent weight
B. Molecular weight
C. Density
D. Volume
Formulas & Calculations
11. Molarity formula is:
A. n/V
B. m/V
C. V/n
D. n×V
12. Molality formula:
A. n/kg solvent
B. n/L
C. g/L
D. mol/g
13. Unit of molality:
A. mol/L
B. mol/kg
C. g/L
D. kg/mol
14. Unit of molarity:
A. mol/kg
B. mol/L
C. g/kg
D. L/mol
15. Mole fraction has:
A. Unit
B. No unit
C. kg unit
D. mol unit
More Conceptual Questions
16. Dilute solution has:
A. Less solute
B. More solute
C. Equal solute
D. No solute
17. Concentrated solution has:
A. Less solute
B. More solute
C. Equal solvent
D. No solvent
18. Saturated solution contains:
A. Maximum solute
B. Minimum solute
C. No solute
D. Only solvent
19. Unsaturated solution:
A. Cannot dissolve more solute
B. Can dissolve more solute
C. Has no solvent
D. Is solid
20. Supersaturated solution is:
A. Stable
B. Unstable
C. Dilute
D. Gas
Numerical/Concept Mix
21. 1 M solution contains:
A. 1 mol/kg
B. 1 mol/L
C. 1 g/L
D. 1 kg/L
22. Increasing temperature affects:
A. Molality
B. Mole fraction
C. Molarity
D. Mass
23. Mass percent formula includes:
A. Mass of solute
B. Mass of solution
C. Both
D. None
24. ppm means:
A. Parts per million
B. Parts per mole
C. Pressure per mole
D. None
25. ppm is used for:
A. Concentrated solutions
B. Very dilute solutions
C. Solids
D. Gases only
Application-Based
26. Which is most concentrated?
A. 1 M
B. 2 M
C. 0.5 M
D. 0.1 M
27. Density is needed to convert:
A. Molality → Mole fraction
B. Molarity → Molality
C. Mass → Mole
D. None
28. Solvent is present in:
A. Less amount
B. Greater amount
C. Equal amount
D. None
29. Solute is present in:
A. Greater amount
B. Lesser amount
C. Equal amount
D. None
30. Water is called:
A. Universal solvent
B. Weak solvent
C. Non-solvent
D. Acid
Advanced MCQs
31. Mole fraction of solute increases when:
A. Solute decreases
B. Solvent decreases
C. Volume increases
D. Temperature decreases
32. Which has highest boiling point?
A. Dilute solution
B. Concentrated solution
C. Pure solvent
D. Gas
33. Colligative properties depend :
A. Nature
B. Number of particles
C. Temperature
D. Volume
34. Ideal solution follows:
A. Raoult’s law
B. Boyle’s law
C. Charles law
D. Dalton law
35. Non-ideal solution deviates due to:
A. Interactions
B. Temperature
C. Pressure
D. Mass
Final Set
36. Example of solid in liquid:
A. Sugar in water
B. Air
C. Brass
D. Hydrogen
37. Example of gas in gas:
A. Air
B. Soda
C. Sugar solution
D. Alloy
38. Example of liquid in liquid:
A. Benzene + Toluene
B. Salt + water
C. Oxygen + water
D. Hydrogen + nitrogen
39. Strong electrolyte:
A. NaCl
B. Glucose
C. Urea
D. Sugar
40. Weak electrolyte:
A. HCl
B. NaOH
C. CH₃COOH
D. NaCl
Last 10 Questions
41. Molality symbol:
A. M
B. m
C. N
D. X
42. Mole fraction symbol:
A. X
B. M
C. m
D. N
43. Normality symbol:
A. N
B. M
C. m
D. X
44. Which is dimensionless?
A. Molarity
B. Molality
C. Mole fraction
D. Normality
45. 1 kg =
A. 100 g
B. 1000 g
C. 10 g
D. 500 g
46. 1 L =
A. 100 mL
B. 1000 mL
C. 10 mL
D. 500 mL
47. Solubility increases with temperature for:
A. Gases
B. Solids
C. Liquids
D. All
48. Gas solubility decreases with:
A. Pressure
B. Temperature
C. Volume
D. Density
49. Henry’s law relates:
A. Pressure & solubility
B. Temperature & solubility
C. Mass & volume
D. Density & mass
50. Example of supersaturated solution:
A. Fresh solution
B. Heated then cooled solution
C. Dilute solution
D. Gas
NUMERICALS
1. Calculate the molar mass of the following compounds
i.Water
ii. Ethylene glycol
iii. Acetic acid
iv. Ethanol
v. Urea
vi. Glycerol
vii. Sugar
viii. Methanol
ix. Benzene
x. Sulphuric acid
2. Calculate the molality and mole fraction of 2.5 g of ethanoic acid in 75 g of benzene.
3. Calculate the molarity and normality of a solution containing 9.8 g of sulphuric acid in 250 cc of the solution.
4. Calculate the mole fraction of ethylene glycol and water in a solution containing 20% of ethylene glycol by mass.
5. Calculate the molality and mole fraction of the solute in aqueous solution containing 3.0 g of urea per 250 g of water.
6. A solution contains 90 g of water, 6.4 g of methanol and 18.4 g of glycerol. What is the mole fraction of glycerol?
7. A solution contains 25% water, 25% ethanol and 50% acetic acid by mass. Calculate the mole fraction of each component.
8. Find the molarity and molality of a 15% solution of sulphuric acid (density = 1.020 g/cc).
9. Calculate the molarity of water if its density is 1000 kg/m³.
10. The mole fraction of benzene in a solution in toluene is 0.50. Calculate the weight percent of benzene in the solution.
11. Calculate the mass percentage of benzene and carbon tetrachloride if 22 g of benzene is dissolved in 122 g of carbon tetrachloride.
12. Calculate the mole fraction of benzene in solution containing 30% by mass in carbon tetrachloride.
13. Calculate the mass of urea required in making 2.5 kg of 0.25 molal aqueous solution.
14. Calculate (a) molality (b) molarity and (c) mole fraction of KI if the density of 20% (mass/mass) aqueous KI is 1.202 g/mL.
15. Concentrated nitric acid used in the laboratory is 68% nitric acid by mass in aqueous solution. What should be the molarity of such a sample of the acid if the density of the solution is 1.504 g/mL ?
CONCLUSION
In conclusion, the chapter on solutions is both theoretical and numerical-based, making it essential to understand the concepts clearly. By learning the types of solutions and different methods of expressing concentration, students can solve problems with confidence.
Regular practice of numericals and a clear understanding of formulas will make this chapter easy and scoring. With the right approach, mastering solutions becomes simple and interesting.