Question

questions of chapter atoms and molecules for class 9th 2020 plz tell me
its very important for me​

Answer 1

at least tell the book name, and the pictures of the questions...

Answer 2

Answer:

here are some important questions

1. State:

(a) Law of Conservation of mass

(b) Law of constant proportion

Answer:

(a) It states that mass can neither be created nor destroyed in a chemical reaction.

(b) Law of constant proportion states that in a chemical compound the elements are always present in a definite proportion by mass.

2. What do you mean by atomicity? What is the atomicity of ozone?

Answer:

The number of atoms constituting a molecule is known as its atomicity.

Ozone (O3) contains 3 oxygen atoms. So its atomicity is 3.

3. Calculate the mass of 1 atom of Hydrogen.

Answer:

One mole of hydrogen weighs = 1 g

∴ 6.02×1023 atoms of hydrogen weigh = 1/ (6.02×1023)

∴ 1 atom of hydrogen weighs = 1.66 ×10−24 g

4. Name a non-metal which is polyatomic.

Answer:

Sulphur (S) called polyatomic because each sulphur molecule (S8) is made up of 8 sulphur atoms.

5. Calculate the mass percentage of oxygen present in HNO3.

Answer:

The molecular mass of HNO3 = the atomic mass of H + the atomic mass of N + 3 × the atomic mass of O = 1 + 14 + 48 = 63 g

Mass percentage of oxygen = (Mass of O in compound/ molecular mass) x 100

= (48/63) x 100 = 76.19%

6. What is Avogadro constant? Write its value.

Answer:

The Avogadro constant is defined as the number of atoms in exactly 12 g of carbon-12.

Avogadro constant or Avogadro number = 6.022 × 1023

7. What do you mean by one mole of a substance?

Answer:

The mole is the amount of substance that contains the same number of particles (atoms/ ions/ molecules/ formula units etc.) as there are atoms in exactly 12 g of carbon-12.

8. How many molecules of water are present in 36 grams of water?

Answer:

Molecular mass of water (H2O) = 2(H)+1(O) = 2×1 + 1×16 = 2 + 16 = 18 gm

Thus, 1 mole of water weighs= 18 g

Or 18g of water contain 1 mole, i.e., 6.023 x 1023 molecules of water.

36 gm of water contain = (36/18) x 6.023 x 1023

= 2 x 6.023 x 1023 = 12.044 x 1023molecules of water

9. Which has more number of atoms: 100g of N2 or 100g of NH3?

Answer:

NH₃ has more atoms than N₂.

10. A group of atoms carrying a fixed charge on them is called _______.

Answer:

Polyatomic ion.