Unit-3: Basic concepts of chemistry

Question 1

What is chemistry?

Answer 1

Chemistry is the study of matter, its properties, and the changes it undergoes.

Question 2

Name two everyday applications of chemistry.

Answer 2

Cooking and cleaning.

Question 3

Mention one role of chemistry in environmental science.

Answer 3

Solving issues like pollution and climate change.

Question 4

How does chemistry contribute to medical advancements?

Answer 4

Through the development of medicines, diagnostics, and surgical materials.

Question 5

Who proposed the atomic theory in 1808?

Answer 5

John Dalton.

Question 6

What are atoms according to Dalton’s atomic theory?

Answer 6

Indivisible particles of matter.

Question 7

According to Dalton, how do atoms of different elements differ?

Answer 7

They differ in mass and properties.

Question 8

What happens to atoms during chemical reactions, according to Dalton’s theory?

Answer 8

They are rearranged but not created or destroyed.

Question 9

Name one limitation of Dalton’s atomic theory.

Answer 9

Atoms are divisible into subatomic particles (protons, neutrons, electrons).

Question 10

Define atomic mass.

Answer 10

The weighted average mass of all isotopes of an element, compared to 1/12th the mass of a carbon-12 atom.

Question 11

What is the atomic mass unit (amu)?

Answer 11

A unit used to express atomic and molecular masses.

Question 12

Calculate the molecular mass of H₂O.

Answer 12

Molecular mass of H₂O = (2 × 1 u) + (1 × 16 u) = 18 u.

Question 13

What is a mole in chemistry?

Answer 13

A unit representing 6.022 × 10^23 particles.

Question 14

What is the molar mass of H₂O?

Answer 14

18 g/mol.

Question 15

How many particles are present in 1 mole of any substance?

Answer 15

6.022 × 10^23.

Question 16

If 2 moles of H₂ are used, how many molecules of H₂ are present?

Answer 16

2 × 6.022 × 10^23 molecules.

Question 17

What is an empirical formula?

Answer 17

The simplest whole-number ratio of atoms in a compound.

Question 18

Give an example of an empirical formula.

Answer 18

CH₂O (for glucose).

Question 19

What is a molecular formula?

Answer 19

The exact number of atoms of each element in a molecule.

Question 20

How is the molecular formula related to the empirical formula?

Answer 20

Molecular Formula = n × Empirical Formula.

Question 21

If the molecular mass of glucose is 180 u, and the empirical formula mass is 30 u, find n.

Answer 21

n = Molecular Mass / Empirical Formula Mass = 180 / 30 = 6.

Question 22

Define a chemical reaction.

Answer 22

A process where reactants are converted to products.

Question 23

Write a balanced chemical equation for the formation of water.

Answer 23

2H₂ + O₂ → 2H₂O.

Question 24

What is stoichiometry?

Answer 24

The calculation of reactants and products in a chemical reaction based on the law of conservation of mass.

Question 25

In the reaction 2H₂ + O₂ → 2H₂O, what is the molar ratio of H₂ to O₂?

Answer 25

2:1.

Question 26

If 4 grams of H₂ are used, how many moles of H₂ are there?

Answer 26

Moles of H₂ = Mass / Molar Mass = 4 / 2 = 2 moles.

Question 27

How many grams of O₂ are required to react with 2 moles of H₂?

Answer 27

1 mole of O₂ is required (molar mass = 32 g/mol), so 32 grams.

Question 28

How many moles of H₂O are produced if 2 moles of H₂ react completely?

Answer 28

2 moles of H₂O.