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Here’s an extensive question paper for Class 11 Chemistry covering Chapters 1 to 5, with a wide
variety of questions and detailed answers.

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### Class 11 Chemistry Question Paper

**Chapters 1 to 5**

**Time: 3 Hours**

**Maximum Marks: 80**

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**General Instructions:**

1. All questions are compulsory.

2. The question paper consists of four sections: A, B, C, and D.

3. Section A contains 1-mark questions.

4. Section B contains 2-mark questions.

5. Section C contains 3-mark questions.

6. Section D contains 5-mark questions.

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### Section A: Multiple Choice Questions (1 Mark Each) [Total: 20 Marks]

1. The number of moles in 12 grams of carbon is:

**a) 1**

**b) 2**

**c) 0.5**
 **d) 6**

**Answer:** a) 1

2. The unit of molarity is:

**a) moles per liter**

**b) grams per liter**

**c) moles per kilogram**

**d) liters per mole**

**Answer:** a) moles per liter

3. Which of the following is an intensive property?

**a) Mass**

**b) Volume**

**c) Density**

**d) Heat**

**Answer:** c) Density

4. The molar mass of NaCl is:

**a) 40 g/mol**

**b) 58.5 g/mol**

**c) 35.5 g/mol**

**d) 22.4 g/mol**

**Answer:** b) 58.5 g/mol

5. The empirical formula of a compound with a molecular formula C₆H₁₂ is:

**a) CH**

**b) C₂H₄**

**c) C₃H₆**

**d) C₆H₁₂**
 **Answer:** b) C₂H₄

6. Which law states that mass is neither created nor destroyed in a chemical reaction?

**a) Law of definite proportions**

**b) Law of conservation of mass**

**c) Law of multiple proportions**

**d) Dalton's law**

**Answer:** b) Law of conservation of mass

7. Avogadro's number is approximately:

**a) \( 6.022 \times 10^{23} \)**

**b) \( 3.011 \times 10^{23} \)**

**c) \( 1.602 \times 10^{-19} \)**

**d) \( 22.4 \)**

**Answer:** a) \( 6.022 \times 10^{23} \)

8. The mass percent of an element in a compound is defined as:

**a) (mass of element / total mass of compound) × 100**

**b) (total mass of compound / mass of element) × 100**

**c) (moles of element / total moles of compound) × 100**

**d) None of the above**

**Answer:** a) (mass of element / total mass of compound) × 100

9. The molecular mass of \( \text{H}_2\text{O} \) is:

**a) 16 g/mol**

**b) 18 g/mol**

**c) 20 g/mol**

**d) 22 g/mol**

**Answer:** b) 18 g/mol
10. The balanced equation for the combustion of propane (C₃H₈) is:

**a) C₃H₈ + 5 O₂ → 3 CO₂ + 4 H₂O**

**b) C₃H₈ + 3 O₂ → 3 CO₂ + 4 H₂O**

**c) C₃H₈ + 4 O₂ → 3 CO₂ + 4 H₂O**

**d) C₃H₈ + 4.5 O₂ → 3 CO₂ + 4 H₂O**

**Answer:** a) C₃H₈ + 5 O₂ → 3 CO₂ + 4 H₂O

11. The atomic number of an element represents:

**a) Number of protons**

**b) Number of neutrons**

**c) Total number of nucleons**

**d) Total mass of the atom**

**Answer:** a) Number of protons

12. Which particle has a negative charge?

**a) Proton**

**b) Neutron**

**c) Electron**

**d) Nucleon**

**Answer:** c) Electron

13. The shape of an s orbital is:

**a) Spherical**

**b) Dumbbell**

**c) Double dumbbell**

**d) Linear**

**Answer:** a) Spherical
14. The principal quantum number (n) indicates:

**a) Size and energy of an orbital**

**b) Shape of an orbital**

**c) Orientation of an orbital**

**d) Spin of an electron**

**Answer:** a) Size and energy of an orbital

15. The maximum number of electrons in a shell is given by the formula:

**a) n²**

**b) 2n²**

**c) n**

**d) 2n**

**Answer:** b) 2n²

16. Which of the following is a characteristic of a metalloid?

**a) Good conductor of heat**

**b) Dull appearance**

**c) High melting point**

**d) All of the above**

**Answer:** d) All of the above

17. The modern periodic table is based on:

**a) Atomic mass**

**b) Atomic number**

**c) Density**

**d) Valency**

**Answer:** b) Atomic number

18. The term "isotopes" refers to atoms of the same element that have:
 **a) Different atomic numbers**

**b) Same number of protons**

**c) Different mass numbers**

**d) Both b and c**

**Answer:** d) Both b and c

19. The period number in the periodic table indicates:

**a) Number of valence electrons**

**b) Number of filled shells**

**c) Number of protons**

**d) Number of neutrons**

**Answer:** b) Number of filled shells

20. The elements in the same group of the periodic table have:

**a) Similar physical properties**

**b) Similar chemical properties**

**c) Same number of valence electrons**

**d) All of the above**

**Answer:** d) All of the above

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### Section B: Short Answer Questions (2 Marks Each) [Total: 20 Marks]

21. **Calculate the number of moles in 50 grams of H₂O.**

**Answer:** Moles of H₂O = mass (g) / molar mass (g/mol) = 50 g / 18 g/mol = 2.78 moles.

22. **Explain the difference between an empirical formula and a molecular formula with examples.**
 **Answer:** The empirical formula represents the simplest ratio (e.g., CH for C₆H₁₂), while the
molecular formula shows actual numbers (C₆H₁₂).

23. **What is the significance of Avogadro's number in chemistry?**

**Answer:** Avogadro's number (6.022 × 10²³) allows us to convert between moles and the number
of particles.

24. **Differentiate between molarity and molality.**

**Answer:** Molarity = moles of solute/volume of solution (L); Molality = moles of solute/mass of

25. **Describe how to identify the limiting reagent in a chemical reaction with an example.**

**Answer:** The limiting reagent is the reactant that gets consumed first, determining the maximum
amount of product formed (e.g., in 2H₂ + O₂ → 2H₂O, if you have more H₂ than O₂, O₂ is the limiting
reagent).

26. **Define the term "ionization energy."**

**Answer:** Ionization energy is the energy required to remove an electron from an atom in its
gaseous state.

27. **What is the principle behind Rutherford’s gold foil experiment?**

**Answer:** The experiment demonstrated that atoms have a small, dense nucleus, as most alpha
particles passed through while some were deflected.

28. **What are valence electrons?**

**Answer:** Valence electrons are the electrons in the outermost shell of an atom, determining its
chemical properties and reactivity.

29. **What is a cov

alent bond?**
 **Answer:** A covalent bond is a chemical bond formed when two atoms share one or more pairs of
electrons.

30. **Explain what isotopes are with examples.**

**Answer:** Isotopes are atoms of the same element with the same number of protons but different
numbers of neutrons (e.g., Carbon-12 and Carbon-14).

31. **What are the characteristics of ionic compounds?**

**Answer:** Ionic compounds have high melting and boiling points, conduct electricity when
dissolved in water, and are generally soluble in water.

32. **What does the term "specific heat capacity" mean?**

**Answer:** Specific heat capacity is the amount of heat required to raise the temperature of 1 gram
of a substance by 1°C.

33. **What is a chemical reaction? Provide an example.**

**Answer:** A chemical reaction is a process where reactants transform into products (e.g.,
combustion of methane: CH₄ + 2 O₂ → CO₂ + 2 H₂O).

34. **How does temperature affect the rate of a chemical reaction?**

**Answer:** Generally, increasing temperature increases reaction rates as particles have more kinetic
energy, leading to more frequent and effective collisions.

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### Section C: Long Answer Questions (3 Marks Each) [Total: 30 Marks]

35. **Explain Dalton's atomic theory and its significance.**

**Answer:** Dalton's atomic theory posits that matter is composed of atoms, which are indivisible
and indestructible. Atoms of the same element are identical, while atoms of different elements differ.
This theory laid the foundation for modern chemistry by introducing the concept of atoms as
fundamental building blocks.
36. **Describe the structure of an atom according to the Bohr model.**

**Answer:** The Bohr model describes the atom as having a dense nucleus containing protons and
neutrons, with electrons orbiting in fixed paths or energy levels. Each orbit corresponds to a specific
energy level, and electrons can move between levels by absorbing or emitting energy.

37. **What is the law of definite proportions? Provide an example.**

**Answer:** The law of definite proportions states that a chemical compound always contains its
component elements in fixed ratio by mass. For example, water (H₂O) is always composed of hydrogen
and oxygen in a 1:8 mass ratio.

38. **Explain the concept of molarity with an example.**

**Answer:** Molarity (M) is a measure of concentration defined as the number of moles of solute per
liter of solution. For example, if 2 moles of NaCl are dissolved in 1 liter of water, the molarity of the
solution is 2 M.

39. **Discuss the role of catalysts in chemical reactions.**

**Answer:** Catalysts are substances that increase the rate of a chemical reaction without being
consumed in the process. They work by lowering the activation energy required for the reaction,
allowing it to proceed more quickly. For example, enzymes in biological systems act as catalysts.

40. **Describe the periodic trends in atomic radius and explain why they occur.**

**Answer:** Atomic radius generally increases down a group due to the addition of electron shells,
which increases the distance between the nucleus and outer electrons. It decreases across a period as
increased nuclear charge pulls electrons closer to the nucleus, resulting in a smaller radius.

41. **Explain the significance of electron configuration in determining the chemical properties of an
element.**

**Answer:** The electron configuration determines how an atom interacts with other atoms,
influencing its reactivity and bonding behavior. Elements with similar configurations (especially in the
outer shell) tend to exhibit similar chemical properties, leading to the formation of groups in the
periodic table.

42. **What are hybridization and its significance in molecular geometry?**

43. **Define "oxidation" and "reduction" and provide an example of a redox reaction.**

**Answer:** Oxidation is the loss of electrons, while reduction is the gain of electrons. In the reaction
between zinc and copper sulfate (Zn + CuSO₄ → ZnSO₄ + Cu), zinc is oxidized (loses electrons), and
copper is reduced (gains electrons).

44. **How does the structure of water contribute to its unique properties?**

**Answer:** Water's polar covalent bonds lead to hydrogen bonding, resulting in high surface tension,
high specific heat, and a solid state (ice) that is less dense than its liquid state. These properties are
crucial for life and various ecological processes.

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### Section D: Essay Questions (5 Marks Each) [Total: 30 Marks]

45. **Discuss the modern periodic table and the periodic law. How does it differ from Mendeleev's
table?**

**Answer:** The modern periodic table is arranged by increasing atomic number, which aligns
elements with similar properties in groups. The periodic law states that the properties of elements are
periodic functions of their atomic numbers. This differs from Mendeleev's table, which was arranged by
atomic mass and had inconsistencies, as some elements were placed in incorrect groups based on mass
rather than properties.

46. **Explain the various types of chemical bonds with examples.**

**Answer:** The main types of chemical bonds include:

- **Ionic bonds:** Formed by the transfer of electrons from one atom to another (e.g., NaCl).

- **Covalent bonds:** Formed by sharing electrons between atoms (e.g., H₂O).

- **Metallic bonds:** Involves a "sea of electrons" shared among a lattice of metal atoms (e.g., Cu).
These bonds determine the properties of substances such as melting points, conductivity, and solubility.
47. **Discuss the concept of pH and its significance in chemistry and biology.**

**Answer:** pH measures the acidity or basicity of a solution, calculated as the negative logarithm of
the hydrogen ion concentration. It ranges from 0 (acidic) to 14 (basic), with 7 being neutral. pH is crucial
in biological systems, affecting enzyme activity, metabolic processes, and the solubility of minerals and
nutrients.

48. **Describe the concept of thermodynamics in chemical reactions, including the laws of
thermodynamics.**

**Answer:** Thermodynamics studies energy changes in chemical reactions.

- **First Law:** Energy cannot be created or destroyed, only transformed.

- **Second Law:** Entropy (disorder) in an isolated system always increases.

- **Third Law:** As temperature approaches absolute zero, entropy approaches a constant minimum.
These principles guide the understanding of reaction spontaneity and energy efficiency.

49. **What is the significance of organic compounds in daily life? Discuss a few examples.**

**Answer:** Organic compounds, primarily based on carbon, are vital for life. Examples include:

- **Carbohydrates:** Provide energy (e.g., glucose).

- **Proteins:** Serve as enzymes and structural components (e.g., hemoglobin).

- **Lipids:** Store energy and form cell membranes (e.g., triglycerides).

Their roles extend to pharmaceuticals, plastics, and fuels, making them integral to various industries.

50. **Explain the process of stoichiometry in balancing chemical equations. Give an example.**

**Answer:** Stoichiometry involves using the coefficients in a balanced chemical equation to relate
quantities of reactants and products. To balance an equation, ensure the same number of each type of
atom appears on both sides. For example, in the combustion of methane:

\[ CH₄ + 2 O₂ → CO₂ + 2 H₂O \]

This shows the ratios of reactants and products, allowing calculations of moles or mass involved in the
reaction.

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### End of Question Paper

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