Question

3. How can we divide molecules according to the number of atoms contain in it? Classify
the following molecules according to it.

Na, O2, S8, P4, K, H2​

Answer 1

Answer:

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Explanation:

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Answer 2

Answer:

1. 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 carbonate.

Ans.

Sodium carbonate + Ethanoic acid → Sodium ethanoate + Carbon dioxide + Water

5.3 g + 6 g → 8.2 g + 2.2 g + 0.9 g

LHS RHS

11.3 g = 11.3 g

(Mass of reactant) (Mass of product)

This shows, that during a chemical reaction mass of reactact = mass of product.

2. 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?

Ans. Ratio of H : O by mass in water is:

Hydrogen : Oxygen → H2O

1 : 8 = 3 : x

x = 8 × 3

∴ 24 g of oxygen gas would be required to react completely with 3 g of hydrogen gas.

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

Ans. The postulate of Dalton's atomic theory that is the result of the law of conservation of mass is-the relative number and kinds of atoms are constant in a given compound. Atoms cannot be created nor destroyed in a chemical reaction.

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

Ans. The relative number and kinds of atoms are constant in a given compounds

1. Define the atomic mass unit.

Ans. One atomic mass unit is equal to exactly one-twelfth (1/12th) the mass of one atom of carbon-12. The relative atomic masses of all elements have been found with respect to an atom of carbon-12.

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

Ans. Atom is too small to be seen with naked eyes. It is measured in nanometres.

1 m = 109 nm

1. Write down the formulae of

(i) Sodium oxide

(ii) Aluminium chloride

(iii) Sodium sulphide

(iv) Magnesium hydroxide

Ans. The formulae. are

(i) Formula bf Sodium Oxide

Symbol → Na O

Charge → +1 –2

Formula → Na2O

(iii) Formula of Sodium Oxide

Symbol → Na S

Charge → + 1 –2

Formula → Na2S

(ii) Formula of aluminium chloride

Symbol → Al Cl

Charge → +3 –1

Formula → A1C13

(iv) Formula of magnesium hydroxide

Symbol → Mg OH

Charge 1

Formula → Mg(OH)2

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