Question

Potassium chlorate decomposes on heating to form potassium chloride and oxygen.When 24.5g of potassium chlorate is decomposed completely.Then 14.9g of potassium chloride is formed.Calculate the mass of oxygen.Which law of chemical combination will govern your answer?

Answer 1

1. Law of conservation of mass : Mass can

neither be created nor can it be destroyed in a

chemical reaction.

2. Law of constant proportions : In a pure

substance same elements are always present in

a definite proportion by weight.

3. Atom : Smallest unit of an element, which may

or may not exist independently, but always takes

part in a chemical reaction.

4. Molecule : Smallest unit of an element or a

compound which always exists independently

and retains the complete physical and chemical

properties of the element or the compound.

5. Atomicity of a molecule of an element : It

is the number of atoms which constitute one

molecule of an element.

6. Molecular formula : The symbolic representation

of the kind and the actual number of atoms in

one molecule of a pure substance, may be an

element or a compound.

7. Atomic mass unit : The mass of 1/12 part of

C-12 (isotope of carbon) is equivalent to one

atomic mass unit.

8. Gram-atomic mass : The atomic mass of an

element expressed in terms of grams.

9. Atomic mass : The number of times an atom

of an element is heavier than 1/12 part of

C-12 (isotope of carbon).

10. Molecular mass : The number of times a

molecule of a pure substance is heavier than

1/12 part of C-12 (isotope of carbon).

11. Gram-molecular mass : The molecular mass

of a pure substance expressed in grams.

12. Mole : A group of 6.022 × 1023 particles (atoms,

molecules, ions, electrons, protons, neutrons,

etc.) of a substance is called mole.

13. Mole number : It is a number which states,

how many times one molecular mass comes

in certain mass of a substance in grams.

IMPORTANT NOTES

3 Atoms and Molecules

Assignments for summative Assessment

I. Very Short Answer Questions (1 Mark)

Previous Years’ Questions

1. State the postulate of Dalton's Atomic Theory which can explain the law of definite proportions?

[2011 (T-II)]

Other Important Questions

1. Find the ratio by mass of the combining elements

$\huge\mathfrak\pink{Hey \: Guys}$

in the compound – C2

H5

OH.

2. Give the formula of the compound formed by

the elements calcium and fluorine.

3. What is the acid radical present in sodium

peroxide?

4. Carbon and silicon have the same valency. What

is the formula of sodium silicate?

5. What is the ratio by number of atoms in