# Atoms And Molecules Science Class 9 ncert questions Answers

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## Atoms And Molecules Science Class 9 ncert questions Answers

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# Class 9 Science Questions With Answers

#### Class 9 Science Questions And Answers:

sodium carbonate + ethanoic acid → sodium ethanoate + carbon dioxide + water

Mass of Sodium carbonate = 5.3g

Mass of ethanoic Acid = 6g

Mass of Sodium ethanoic acid = 8.2g

Mass of water = 0.9g

We knock that according to the law of conservation of mass-

Mass of reactants = Mass of products

5.3g + 6g = 8.2g + 2.2g + 0.9g

11.3g = 11.3g

Hence, the given observations are satisfied the law of conservation of mass.

Given ratio of Hydrogen and Oxyden - 1:8

It means- 1g of Hydrogen gas required 8g Oxygen to reaction with Hydrogen

Therefore, 3g of Hydrogen gas required = 3 x 8 = 24g

So, 24g Oxygen is required to react completely with Hydrogen gas.

The second postulate of Dalton's atomic theory is the result of the law of conservation of mass.

That is as follow-

"Atoms are indivisible particles, which can neither be created nor be destroyed in a chemical reaction".

The sixth postulate of Dalton's atomic theory explains the law of definite proportions.

That is as follow-

"The ralative number and kind of atoms in a given compound remains constatnt".

An atomic mass unit or  amu is one twelfth of the mass of an unbound atom of carbon -12 isotope. This is approximetely 1.67377 x 10 -27 kilogram (kg).

The relative atomic mass of the atom of an element is defined as the average mass of the atom, as compared to 1/12th the mass of one carbon-12 atom.

Atomic mass unit is abbreviated as 'amu' but on IUPAC latest recommendation, it is writen as 'u'.

Atoms are very small tiny particles. It is so small that can not be seen with a nacked eyes. Also, an another reason - the atom of an element does not exist independently.

(i) Sodium oxide : Na2O

(ii) Aluminium chloride : AlCl3

(iii) Sodium Sulphate : Na2S

(iv) Magnesium hydroxide : Mg(OH)2

The Molecular mass of H2 = 2 x atomic mass of H

= 2 x 1 = 2u

The molecular mass of O2 = 2 x atomic mass of O

= 2 x 16 = 32u

The molecular mass of Cl2 = 2 x atomic mass of Cl

= 2 x 35.5 = 71u

The molecular mass of CO2 = atomic mass of C + 2 x atomic mass of O

= 12 + 2 x 16 = 44u

The molecular mass of CH4 = atomic mass of C + 4 x atomic mass of H

= 12 + 4 x 1 = 16u

The molecular mass of C2H= 2 x atomic mass of C + 6 x atomic mass of H

= 2 x 12 + 6 x 1 = 30u

The molecular mass of C2H= 2 x atomic mass of C + 4 x atomic mass of H

= 2 x 12 + 4 x 1 = 28u

The molecular mass of NH= atomic mass of N + 3 x atomic mass of H

= 14 + 3 x 1 = 17u

The molecular mass of CH3OH = atomic mass of C + 4 x atomic mass of H + atomic mass of O

= 12 + 4 x 1 + 16 = 32u

### Study Materials

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#### Class 9 Science Atoms And Molecules 2023-2024 Latest Syllabus

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