CBSE Class 9 Chemistry Atoms And Molecules Worksheet Set C

Question: Which of the following correctly represents 360 g of water?
(i) 2 moles of H₂0
(ii) 20 moles of water
(iii) 6.022 × 10²³ molecules of water
(iv) 1.2044×10²⁵ molecules of water
(a) (i)
(b) (i) and (iv)
(c) (ii) and (iii)
(d) (ii) and (iv)
Answer: d

Question: Which of the following would weigh the highest?
a) 0.2 mole of sucrose (C₁₂H₂₂O₁₁)
b) 2 moles of CO₂
c) 2 moles of CaCO₃
d) 10 moles of H₂O
Answer: c

Question: The chemical symbol for nitrogen gas is
a) Ni
b) N₂
c) N⁺
d) N
Answer: b

Question: Which of the following contains maximum number of molecules?
a) 1 g CO₂
b) 1 g N₂
c) 1 g H₂
d) 1 g CH₄
Answer: c

Question: The chemical symbol for sodium is
a) So
b) Sd
c) NA
d) Na
Answer: d

Question: Which of the following has maximum number of atoms?
a) 18 g of H₂O
b) 18 g of O₂
c) 18 g of CO₂
d) 18 g of CH₄
Answer: d

Question: Mass of one atom of oxygen is

Answer: a

Question: Which of the following statements is not true about an atom?
a) Atoms are not able to exist independently
b) Atoms are the basic units from which molecules and ions are formed
c) Atoms are always neutral in nature
d) Atoms aggregate in large numbers to form the matter that we can see, feel or touch
Answer: a

Question: A change in the physical state can be brought about
a) only when energy is given to the system
b) only when energy is taken out from the system
c) when energy is either given to, or taken out from the system
d) without any energy change
Answer: c

Question: Which of the following represent correct chemical formula? Name it.
a) CaCl
b) BiPO₄
c) NaSO₄
d) NaS
Answer: b

Question: 3.42 g of sucrose are dissolved in 18 g of water in a beaker. The number of oxygen atoms in the solution are
a) 6.68 × 10²³
b) 6.09 × 10²²
c) 6.022 × 10²³
d) 6.022 × 10²¹
Answer: a

Give the formulae of the compounds formed from the following sets of elements

Question: Calcium and fluorine
Answer: CaF₂

Question: Hydrogen and sulphur
Answer: H₂S

Question: Nitrogen and hydrogen
Answer: NH₃

Question: Carbon and chlorine
Answer: CCl₄

Question: Sodium and oxygen
Answer: Na₂O

Question: Carbon and oxygen
Answer: CO, CO₂

Express each of the following in kilograms

Question: 5.84 × 10⁻³ mg
Answer: 5.84 × 10⁻⁹ kg

Question: 58.34 g
Answer: 5.834 × 10⁻² kg

Question: 0.584 g
Answer: 5.84 × 10⁻⁴ kg

Question: 5.873 × 10⁻²¹ g
Answer: 5.873 × 10⁻²⁴ kg

Fill in the blanks

Question: Formula of sodium carbonate is and that of ammonium sulphate is __________.
Answer: Na₂CO₃; (NH₄)₂SO₄

Question: A group of atoms carrying a fixed charge on them is called __________.
Answer: Polyatomic ion

Question: In a chemical reaction, the sum of the masses of the reactants and products remains unchanged. This is called __________.
Answer: Law of conservation of mass

Question: The formula unit mass of Ca₃(PO₄)₂ is __________.
Answer: (3 × atomic mass of Ca) + (2 × atomic mass of P) + (8 × atomic mass of O) = 310

Write the molecular formulae for the following compounds

Question: Copper (II) bromide
Answer: CuBr₂

Question: Aluminium (III) nitrate
Answer: Al(NO₃)₃

Question: Calcium (II) phosphate
Answer: Ca₃(PO₄)₂

Question: Iron (III) sulphide
Answer: Fe₂S₃

Question: Mercury (II) chloride
Answer: HgCl₂

Question: Magnesium (II) acetate
Answer: Mg(CH₃COO)₂

State the number of atoms present in each of the following chemical species

Question: CO₃²⁻
Answer: 4

Question: PO₄³⁻
Answer: 5

Question: P₂O₅
Answer: 7

Question: CO
Answer: 2

Find the ratio by mass of the combining elements in the following compounds. (You may use Appendix-III)

Question: CaCO₃
Answer: Ca : C : O₃ = 40 : 12 : (16 × 3) = 40 : 12 : 48 = 10 : 3 : 12

Question: MgCl₂
Answer: Mg : Cl₂ = 24 : (35.55 × 2) = 24 : 71

Question: H₂SO₄
Answer: H₂ : S : O₄ = (1 × 2) : 32 : (16 × 4) = 2 : 32 : 64 = 1 : 16 : 32

Question: C₂H₅OH
Answer: C₂ : H₆ : O = (12 × 2) : (1 × 6) : 16 = 24 : 6 : 16 = 12 : 3 : 8

Question: NH₃
Answer: N : H₃ = 14 : (1 × 3) = 14 : 3

Question: Ca(OH)₂
Answer: Ca : O₂ : H₂ = 40 : (16 × 2) : (1 × 2) = 40 : 32 : 2 = 20 : 16 : 1