HS 2nd year Chemistry Unit 1: Solutions

 

🔹 Topic 1.1: Types of Solutions

Q1. What is a solution? Explain types of solutions with examples.
Ans: A solution is a homogeneous mixture of two or more components. The component in larger quantity is called the solvent, and the one in lesser quantity is the solute. Types of solutions include:

• Gas in gas (e.g., air)

• Liquid in liquid (e.g., ethanol in water)

• Solid in liquid (e.g., salt in water)

• Gas in liquid (e.g., oxygen in water)

Keywords:

• Solution = দ্রবণ

• Homogeneous = সজাতীয়

• Solvent = দ্রাবক

• Solute = দ্রব্য

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🔹 Topic 1.2: Expressing Concentration of Solutions

Q2. Write five methods to express the concentration of solutions.
Ans:

1. Mass % (w/w) = (Mass of solute / Mass of solution) × 100

2. Volume % (v/v) = (Volume of solute / Volume of solution) × 100

3. Mass by volume % (w/v) = (Mass of solute / Volume of solution in mL) × 100

4. Parts per million (ppm) = (Mass of component / Total mass) × 10⁶

5. Mole fraction (x) = Moles of component / Total moles

6. Molarity (M) = Moles of solute / Volume of solution in L

7. Molality (m) = Moles of solute / Mass of solvent in kg

Keywords:

• Concentration = ঘনত্ব

• Mass = ভর

• Volume = আয়তন

• Mole = মোল

• Fraction = ভগ্নাংশ

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🔹 Topic 1.3: Solubility

Q3. What is solubility? How does temperature and pressure affect it?
Ans:
Solubility is the maximum amount of solute that can dissolve in a solvent at a particular temperature and pressure.

• Effect of temperature: Solubility of solids increases if dissolution is endothermic.

• Effect of pressure: Little effect on solids, but for gases, solubility increases with pressure.

Keywords:

• Solubility = দ্রাব্যতা

• Temperature = তাপমাত্রা

• Pressure = চাপ

• Endothermic = উষ্ণগ্রাহী

• Exothermic = তাপ নির্গতকারী

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🔹 Topic 1.3.2: Henry’s Law

Q4. State Henry’s Law and give its application.
Ans:
Henry’s Law: The solubility of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid.
p = KH × x (KH = Henry’s constant)
Applications:

• Bottling of soft drinks

• Scuba diving

• Breathing at high altitudes

Keywords:

• Partial pressure = আংশিক চাপ

• Constant = ধ্রুবক

• Solubility = দ্রাব্যতা

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🔹 Topic 1.4: Vapour Pressure of Liquid Solutions

Q5. State Raoult’s Law.
Ans:
Raoult’s Law: The partial vapour pressure of each volatile component of a solution is proportional to its mole fraction.
p₁ = x₁p₁⁰ and p₂ = x₂p₂⁰

Keywords:

• Vapour pressure = বাষ্পচাপ

• Mole fraction = মোল ভগ্নাংশ

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🔹 Topic 1.5: Ideal and Non-Ideal Solutions

Q6. Distinguish between ideal and non-ideal solutions.
Ans:

• Ideal solution obeys Raoult’s law at all compositions. ΔHmix = 0 and ΔVmix = 0

• Non-ideal solution shows deviation from Raoult’s law.

  • Positive deviation: Weak A-B interactions

  • Negative deviation: Strong A-B interactions

Keywords:

• Ideal = আদর্শ

• Deviation = বিচ্যুতি

• Interaction = পারস্পরিক ক্রিয়া

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🔹 Topic 1.6: Colligative Properties

Q7. What are colligative properties? List them.
Ans:
Colligative properties are properties that depend only on the number of solute particles in a solution, not on their nature.
They include:

1. Relative lowering of vapour pressure

2. Elevation of boiling point

3. Depression of freezing point

4. Osmotic pressure

Keywords:

• Colligative = সম্মিলিত

• Boiling point = স্ফুটনাঙ্ক

• Freezing point = হিমাঙ্ক

• Osmosis = অভিস্রবণ

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🔹 Topic 1.7: Abnormal Molar Mass and van’t Hoff Factor

Q8. What is van’t Hoff factor? What is its significance?
Ans:
Van’t Hoff factor (i) accounts for the degree of association or dissociation of solutes in a solution.

• i = observed colligative property / calculated colligative property

• i > 1 for dissociation, i < 1 for association

Keywords:

• Association = যুক্তি

• Dissociation = বিযুক্তি

• Factor = গুণনীয়ক

🧪 Worksheet: Chapter 1 – Solutions

🔹 Section A: Short Answer Questions (2 marks each)

1. Define a binary solution.

2. What is the difference between solute and solvent?

3. Write the formula for mole fraction.

4. State Henry’s Law.

5. Why is molality preferred over molarity in temperature-based calculations?

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🔹 Section B: Long Answer Questions (5 marks each)

6. Explain any four methods of expressing concentration of solutions with formulae.

7. Describe the effects of temperature and pressure on the solubility of gases in liquids.

8. Differentiate between ideal and non-ideal solutions with suitable examples.

9. What are colligative properties? Explain any two of them in brief.

10. Explain the van’t Hoff factor. How does it affect molar mass calculations?

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🔹 Section C: Fill in the Blanks (1 mark each)

11. The component present in larger quantity in a solution is called __________.

12. Vapour pressure of a solution is __________ than that of the pure solvent.

13. Raoult’s law relates vapour pressure to __________ of the component.

14. The pressure required to stop osmosis is called __________.

15. A solution that obeys Raoult’s Law at all concentrations is called __________.

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🔹 Section D: Multiple Choice Questions (1 mark each)

16. Which of the following is not a colligative property?
    a) Boiling point elevation
    b) Vapour pressure
    c) Osmotic pressure
    d) Freezing point depression

17. Mole fraction is a __________ quantity.
    a) Dimensionless
    b) Dependent on volume
    c) Dependent on mass
    d) None of these

18. Henry’s law states that solubility of a gas is proportional to:
    a) Volume of gas
    b) Temperature
    c) Partial pressure of gas
    d) Density of gas

19. In positive deviation from Raoult’s law, A–B interactions are:
    a) Stronger
    b) Weaker
    c) Same
    d) Non-existent

20. The value of van’t Hoff factor (i) for KCl is approximately:
    a) 1
    b) 0.5
    c) 2
    d) 3

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🔹 Section E: Glossary (Key Terms in Bengali)

Term	Bengali Meaning
Solution	দ্রবণ
Solute	দ্রব্য
Solvent	দ্রাবক
Concentration	ঘনত্ব
Mole fraction	মোল ভগ্নাংশ
Vapour pressure	বাষ্পচাপ
Boiling point	স্ফুটনাঙ্ক
Freezing point	হিমাঙ্ক
Osmosis	অভিস্রবণ
Ideal solution	আদর্শ দ্রবণ
Deviation	বিচ্যুতি
Association	যুক্তিকরণ
Dissociation	বিযুক্তিকরণ