Write down the formulae of sodium oxide.

Important Questions on Atoms and Molecules

EASY

9th CBSE

IMPORTANT

SCIENCE TEXTBOOK FOR CLASS IX>Chapter 3 - Atoms and Molecules>Questions>Q 4

How many atoms are present in a
(i) ${\mathrm{H}}_2\mathrm{S}$ molecule and
(ii) ${\mathrm{P}\mathrm{O}}_4^{3-}$ ion?

HARD

9th CBSE

IMPORTANT

SCIENCE TEXTBOOK FOR CLASS IX>Chapter 3 - Atoms and Molecules>Questions>Q 1

Calculate the molecular masses of ${\mathrm{H}}_2, {\mathrm{O}}_2, \mathrm{C}{\mathrm{l}}_2, \mathrm{C}{\mathrm{O}}_2, \mathrm{C}{\mathrm{H}}_4, {\mathrm{C}}_2{\mathrm{H}}_6, {\mathrm{C}}_2{\mathrm{H}}_4, \mathrm{N}{\mathrm{H}}_3, \mathrm{C}{\mathrm{H}}_3\mathrm{O}\mathrm{H}$.
 

MEDIUM

9th CBSE

IMPORTANT

SCIENCE TEXTBOOK FOR CLASS IX>Chapter 3 - Atoms and Molecules>Questions>Q 2

Calculate the formula unit masses of $\mathrm{Z}\mathrm{n}\mathrm{O}, \mathrm{N}{\mathrm{a}}_2\mathrm{O}, {\mathrm{K}}_2\mathrm{C}{\mathrm{O}}_3,$ given atomic masses of $\mathrm{Z}\mathrm{n}=65 \mathrm{u}, \mathrm{N}\mathrm{a}=23 \mathrm{u}, \mathrm{K}=39 \mathrm{u}, \mathrm{C}=12 \mathrm{u},$ and $\mathrm{O}=16 \mathrm{u}.$

MEDIUM

9th CBSE

IMPORTANT

SCIENCE TEXTBOOK FOR CLASS IX>Chapter 3 - Atoms and Molecules>Questions>Q 1

If one mole of carbon atoms weighs $12$ gram, what is the mass (in grams) of $1$ atom of carbon? (Avogadro number$=6.022\times {10}^{23}$).

MEDIUM

9th CBSE

IMPORTANT

SCIENCE TEXTBOOK FOR CLASS IX>Chapter 3 - Atoms and Molecules>Questions>Q 2

Which has more number of atoms, $100$ grams of sodium or $100$ grams of iron (Given, atomic mass of $\mathrm{N}\mathrm{a}=23 \mathrm{u}, \mathrm{F}\mathrm{e}=56 \mathrm{u}$, Avogadro number $=6.022\times {10}^{23}$)?

HARD

9th CBSE

IMPORTANT

SCIENCE TEXTBOOK FOR CLASS IX>Chapter 3 - Atoms and Molecules>Exercises>Q 2

When $3.0 \mathrm{g}$ of carbon is burnt in $8.00 \mathrm{g}$ oxygen, $11.00 \mathrm{g}$ of carbon dioxide is produced. What mass of carbon dioxide will be formed when $3.00 \mathrm{g}$ of carbon is burnt in $50.00 \mathrm{g}$ of oxygen? Which law of chemical combination will govern your answer?

MEDIUM

9th CBSE

IMPORTANT

SCIENCE TEXTBOOK FOR CLASS IX>Chapter 3 - Atoms and Molecules>Exercises>Q 5

Give the names of the elements present in the following compounds.
(a) Quick lime
(b) Hydrogen bromide
(c) Baking powder
(d) Potassium sulphate.

MEDIUM

9th CBSE

IMPORTANT

SCIENCE TEXTBOOK FOR CLASS IX>Chapter 3 - Atoms and Molecules>Exercises>Q 6

Calculate the molar mass of the following substances.
(a) Ethyne, ${\mathrm{C}}_2{\mathrm{H}}_2$
(b) Sulphur molecule, ${\mathrm{S}}_8$ 
(c) Phosphorus molecule, ${\mathrm{P}}_4$ (Atomic mass of Phosphorus = $31 \mathrm{u}$)
(d) Hydrochloric acid, $\mathrm{H}\mathrm{C}\mathrm{l}$
(e) Nitric acid, $\mathrm{H}\mathrm{N}{\mathrm{O}}_3$.