Atoms and Molecules NCERT Solution, study material, CBSE Notes

NCERT Solution: Atoms and Molecules

In a reaction, 5.3 g of sodium carbonate reacted with 6 g of ethanoic acid.

In a reaction, 5.3 g of sodium carbonate reacted with 6 g of ethanoic acid. The products were 2.2 g of carbon dioxide, 0.9 g water and 8.2 g of sodium ethanoate. Show that these observations are in agreement with the law of conservation of mass.

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

Answer

In the given reaction, sodium carbonate reacts with ethanoic acid to produce sodium ethanoate, carbon dioxide, and water.
Sodium Carbonate + Ethanoic acid → sodium ethanoate + carbon dioxide + water

Mass of sodium carbonate = 5.3 g (Given)
Mass of ethanoic acid = 6 g (Given)
Mass of sodium ethanoate = 8.2 g (Given)
Mass of carbon dioxide = 2.2 g (Given)
Mass of water = 0.9 g (Given)

Now, total mass before the reaction = (5.3 + 6) g
= 11.3 g

And, total mass after the reaction = (8.2 + 2.2 + 0.9) g
= 11.3 g

∴ Total mass before the reaction = Total mass after the reaction

Hence, the given observations are in agreement with the law of conservation of mass.

Hydrogen and oxygen combine in the ratio of 1:8 by mass to form water. What mass of oxygen gas would be required to react completely with 3 g of hydrogen gas?

It is given that the ratio of hydrogen and oxygen by mass to form water is 1:8.

Then, the mass of oxygen gas required to react completely with 1 g of hydrogen gas is 8 g.

Therefore, the mass of oxygen gas required to react completely with 3 g of hydrogen gas is 8 × 3 g = 24 g.

Which postulate of Dalton's atomic theory is the result of the law of conservation of mass?

The postulate of Dalton :"Atoms are indivisible particles, which can not be created or destroyed in a chemical reaction" is the result of the law of conservation of mass.

Which postulate of Dalton's atomic theory can explain the law of definite proportions?

The postulate of Dalton, “The relative number and kinds of atoms are constant in a given compound”, can explain the law of definite proportions.

Define atomic mass unit.

Mass unit equal to exactly one-twelfth the mass of one atom of carbon-12 is called one atomic mass unit. It is written as 'u'.

Why is it not possible to see an atom with naked eyes?

The size of an atom is so small that it is not possible to see it with naked eyes. Also, the atom of an element does not exist independently

Write down the formulae of

(i) sodium oxide

→ Na₂O

(ii) aluminium chloride

→ AlCl₃

(iii) sodium sulphide