Chapter 3: Atoms and Molecules
Learning Notes (Set 3) for Class 9 Science

Question 1: What is the Law of Multiple Proportions?

Answer: When two elements combine to form more than one compound, the masses of one element that combine with a fixed mass of the other are in a ratio of small whole numbers.

Question 2: How did Dalton's atomic theory explain the Law of Conservation of Mass?

Answer: It stated that atoms are indivisible particles that can neither be created nor destroyed in a chemical reaction.

Question 3: What is the formula for calculating the number of moles (n)?

Answer: n = Given mass / Molar mass.

You are on Chapter 3: Atoms and Molecules (Learning Notes for Class 9 Science) Set 3

Question 4: What is an ionic compound?

Answer: A compound formed by the transfer of electrons between a metal and a non-metal, creating positively and negatively charged ions.

Question 5: What is the chemical formula for Calcium Carbonate?

Answer: CaCO₃.

Question 6: What is a chemical formula?

Answer: A symbolic representation of the composition of a compound, showing the type and number of atoms of each element.

Question 7: What is the unit of molar mass?

Answer: grams per mole (g/mol).

Question 8: What is the atomicity of a hydrogen molecule (H₂)?

Answer: 2, because it contains two hydrogen atoms.

You are on Chapter 3: Atoms and Molecules (Learning Notes for Class 9 Science) Set 3

Question 9: What is the mass of one mole of a substance?

Answer: The molar mass, which is its atomic or molecular mass in grams.

Question 10: Who proposed the Law of Definite Proportions?

Answer: Joseph Proust.