KSEEB Solutions for Class 9 Science Chapter 3 Atoms and Molecules

Karnataka Board Class 9 Science Chapter 3 Atoms and Molecules

KSEEB Solutions for Class 9 Science Chapter 3 Intext Questions

KSEEB Solutions For Class 9 Science Chapter 3 Question 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.
Sodium carbonate + ethanoic acid ➝ sodium ethanoate + carbon dioxide + water
Answer:
Sodium carbonate + ethanoic acid ➝ sodium ethanoate + carbon dioxide + water
5.3 + 6 ➝ 8.2 + 2.2 + 0.9
= 11.3 g = 11.3 g
Weight of reactants is equal to weight of products. This observation is in agreement with the law of conservation of mass.

KSEEB Solutions For Class 9 Science Atoms And Molecules Question 2.
Hydrogen and Oxygen combine in the ratio or 1 : 8 by mass to form water. What mass of oxygen gas would be required to react completely with 3 g of hydrogen gas?
Answer:
24 g of oxygen gas would be required to react completely with 3 g of hydrogen gas. Because in water the ratio of the mass of hydrogen to the mass of oxygen is always 1 : 8.

Atoms And Molecules Class 9 Notes KSEEB Question 3.
Which postulate of Dalton’s atomic theory is the result of the law of conservation of mass?
Answer:
The relative number and kinds of atoms are constant in a given compound. This postulate is the result of the law of conservation of mass.

KSEEB Solutions For Class 9 Science Question 4.
Which postulate of Dalton’s atomic theory can explain the law of definite proportions?
Answer:
Atoms combine in the ratio of small whole numbers to form compounds. This postulate explains the law of definite proportions.

Atoms And Molecules Class 9 KSEEB Solutions Question 1.
Define the atomic mass unit.
Answer:
One atomic mass unit is a mass unit equal to exactly one-twelfth (1/12^th) the mass of one atom of carbon-12.

KSEEB Solutions For Class 9 Science Structure Of Atom Question 2.
Why is it not possible to see an atom with naked eyes?
Answer:
Atoms are very small, they are smaller than anything that we can imagine or compare with. Therefore it is not possible to see an atom with naked eyes.

KSEEB Solutions Class 9 Science Question 1.
Write down the formulae of:

sodium oxide
alluminium chloride
sodium sulphide
magnesium hydroxide

Answer:

sodium oxide: Na₂O
aluminium chloride: Al₂Cl₃
sodium sulphide : NaS
magnesium hydroxide: Mg(OH)₂

KSEEB Solutions Science Class 9 Question 2.
Write down the names of compounds represented by the following formulae:

Al₂(SO₄)₃
CaCl₂
K₂SO₄
KNO₃
CaCO₃

Answer:

Al₂(SO₄)₃: Aluminium sulphate
CaCl₂: Calcium chloride
K₂SO₄: potassium sulphate
KNO₃: potassium nitrate
CaCO₃: calcium carbonate

KSEEB Solutions For Class 9 Question 3.
what is meant by the term chemical formula?
Answer:
The chemical formula of a compound is a symbolic representation of its composition.

KSEEB Solutions For Class 9 Science Chapter 3 Atoms And Molecules Question 4.
How many atoms are present in a
i) H₂S molecule and
ii) PO₄^3- ion?
Answer:
i) H₂S molecule:

ii) PO₄^3- ion

9th Class Science Question Answer In Kannada Question 1.
Calculate the molecular masses of
H₂, O₂, Cl₂, CO₂, CH₄, C₂H₆, C₂H₄, NH₃, CH₃OH.
Answer:
i) H₂
= 2 × H
= 2 × 1
= 2u

ii) O₂
= 2 × O
= 2 × 16
= 32u

iii) Cl₂
= 2 × Cl
= 2 × 35.5
= 7lu

iv) CO₂
= 1 × 12 + 2 × O
= 1 × 12 + 2 × 16
= 12 + 32
= 44u

v) CH₄
= 1 × 12 + 4 × 1
= 12 + 4
= 16u

vi) C₂H₆
= 2 × 12 + 6 × 1
= 24 + 6
= 30u

vii) C₂H₄
= 2 × 12 + 4 × 1
= 24 + 4
= 28u

viii) NH₃
= 14 × 1 + 3 × 1
= 14 + 3
= 17u

ix) CH₃OH
= 12 × 1 + 3 × 1 + 16 × 1 + 1 × 1
= 12 + 3 + 16 + 1
= 32u

KSEEB Solutions For 9th Class Science Question 2.
Calculate the formula unit masses of ZnO, Na₂O, K₂CO₃ given atomic masses of Zn = 65u, Na = 23u, K = 39u, C = 12u and O = 16u.
Answer:
i) ZnO
(Automic mass of Zn) + (Automic mass of O)
= 65 + 16 = 81u.

ii) Na₂O
(2 × Automic mass of Na) + (Automic mass of O)
= 2 × 23 + 1 × 16
= 46 + 16
= 62u.

iii) K₂CO₃
(2 × Atomic mass of K)+ (Atomic mass of C) + (3 × Atomic mass of oxygen)
= 2 × 39 + 12 × 1 + 16 × 3
= 78 + 12 + 48
= 138u.

Karnataka State Syllabus For Class 9 Science Question 1.
If one mole of carbon atoms weighs 12 gms, what is the mass (in gms) of 1 atom of carbon?
Answer:
Number of moles = n
Given mass = m
molar mass = M
Given the number of particles = N
Avogadro number of particles = N₀
i) Atomic mass of carbon = 12u.
Atomic mass of one mole of carbon=12g
But Atomic mass of carbon = 12 g mass of 6.022 × 10²³ carbon atoms = 12g.

∴ Mass of carbon atoms
= 1.9926 x 10^-23 gm.

KSEEB Science Solutions For Class 9 Question 2.
Which has more number of atoms, 100 g, 100 gms of sodium or 100 gms of sodium or 100 gms of iron (given, the atomic mass of Na=23u, Fe = 56u).
Answer:
Atomic mass of sodium = 23u (data)
It means the gram atomic mass of sodium = 23 gm
Now atoms present in 23 gm sodium = 6.022 × 10²³

It means Number of atoms in 100 gm sodium = 1.6753 × 10²⁴
∴ 100 gm sodium has more number of atoms rather than 100 gms of iron.

KSEEB Solutions for Class 9 Science Chapter 3 Textbook Exercises

9th Science KSEEB Solutions Question 1.
A 0.24 g sample of a compound of oxygen and boron was found by analysis to contain 0.096g of boron and 0.144 g of oxygen. Calculate the percentage composition of the compound by weight.
Answer:
Mass of Boron = 0.096 g (Data)
Mass of Oxygen = 0.144g (Data)
Given mass = 0.24 g (Data)
∴ The percentage composition of Boron

∴ The percentage of O₂ = \(\frac{0.144}{0.24}\) × 100
= 60%.

KSEEB Solutions For Class 9th Science Question 2.
When 3.00 g of carbon is burnt in 8.009 of oxygen, 11.00 g of carbon dioxide is produced. What mass of carbon dioxide will be formed when 3.00 g of carbon is burnt in 50,000 g of oxygen? Which law of Chemical combination will govern your answer?
Answer:
3.0 g of carbon is burnt in 8.00 g of oxygen, 11.00 g of carbon dioxide is produced.
But when 3 g of carbon is burnt in 50 g of oxygen, only 3 g of carbon reacts with 8 g of oxygen.
Remaining 42 gm of oxygen will not react.
11 gm of carbon dioxide is produced.
∴ Our answer obeys law of constant proportion.

KSEEB Solutions 9th Science Question 3.
What are polyatomic ions? Give examples.
Answer:
A group of atoms carrying a charge is known as a polyatomic ion.

KSEEB Solutions For 9th Science Question 4.
Write the chemical formulae of the following.
(a) Magnesium chloride
(b) Calcium oxide
(c) Copper nitrate
(d) Aluminium chloride
(e) Calcium carbonate
Answer:
(a) Magnesium chloride : MgCl₂
(b) Calcium oxide : CaO
(c) Copper nitrate : Cu(NO₃)₂
(d) Aluminium chloride : AlCl₃
(e) Calcium carbonate : CaCO₃.

9th Class Science Question Answer In Kannada Medium Question 5.
Give the names of the elements present in the following compounds.
(a) Quick lime
(b) Hydrogen bromide
(c) Baking powder
(d) Potassium sulphate
Answer:
(a) Quick lime: Calcium, carbon, oxygen
(b) Hydrogen bromide: Hydrogen, Bromine
(c) Baking powder: Sodium, Bicarbonate
(d) Potassium sulphate: Potassium, Sulphur, Oxygen.

KSEEB 9th Science Solutions Question 6.
Calculate the molar mass of the following substances.
(a) Ethyne, C₂H₂
(b) Sulphur molecule, S₈
(c) Phosphorus Molecule, P₄ (Atomic mass of phosphorus = 31)
(d) Hydrochloric acid, HCl
(e) Nitric acid HNO₃.
Answer:
(a) Ethyne C₂H₂
Molar Mass = 2 × 12 + 2 × 1
= 24 + 2
= 26 g.

(b) Molar mass of Sulphur molecule
= 8 × 32
= 256 g.

(d) Molar mass of Hydrochloric acid = HCl
= 1 + 35.5
= 36.5 g.

(e) Molar mass of HNO₃
= 1 + 14 + 3 × 16
= 15 + 48
= 63 gm.

Class 9 Science ಉತ್ತರಗಳು Karnataka State Board Solutions Question 7.
What is the mass of –
(a) 1 mole of nitrogen atoms?
(b) 4 moles of aluminium atoms (Atomic mass of Aluminium = 27)
(c) 10 moles of Sodium Sulphite (Na₂SO₃)
Answer:
(a) Mass of 1 mole of nitrogen= 14g.

(b) Mass of 4 moles of Aluminium
= 4 × 27
= 108 g.

9th Standard Science Notes Question 8.
Convert into mole:
(a) 12 g of oxygen gas
(b) 20 g of water
(c) 22 g of carbon dioxide
Answer:
(a) 32gm of oxygen means 1 mole
12gm oxygen means \(\frac{12}{32}\) mole
∴ 12g of oxygen gas = 0.375 mole
(b) 18 gm of water means = 1 mole
20 gm of water means \(\frac{20}{18}\) mole = 1.11 mole
(c) 22 g of carbon dioxide means
\(\frac{22}{44}\) = 0.5 mole.

9th Standard Science Question Answer Question 9.
What is the mass of:
(a) 0.2 mole of oxygen atoms?
(b) 0.5 mole of water molecules?
Answer:
(a) Mass of 1 mole of oxygen = 16 g
Mass of 0.2 mole of oxygen = 0.2 × 16
= 3.2 g.
(b) Mass of 1 molecule of water= 18 gm.
Mass of 0.5 mole of water = 0.5 × 18
= 9 gm.

Karnataka State Syllabus For Class 9 Science Notes Question 10.
Calculate the number of molecules of sulphur (S₈) present in 16 g of solid sulphur.
Answer:
One mole of Sulphur (S) = 8 × 32
= 256 gm.
256 g of solid sulphur = 6.022 × 10²³ molecules.
KSEEB Solutions For Class 9 Science Structure Of Atom
= 3.76 × 10²²
(Approximate)

Question 11.
Calculate the number of aluminium ions present in 0.0519 of aluminium oxide.
(Hint: The mass of an ion is the same as that of an atom of the same element. Atomic mass of Al = 27 u).
Answer:
One mole of Aluminium oxide
= 2 × 27+ 3 × 16
= 54 + 48
= 102 g.
102 g of Al₂O₃ = 6.022 × 10²³ moles (aluminium oxide)
KSEEB Solutions Class 9 Science
It means Aluminium present in 0.051 gm
= 3.011 × 10²⁰ Aluminium oxide molecules
Number of Al ions in one mole of Al₂O₃ = 2
∴ Number of Al Ions In 3.011 × 10²⁶ molecules
0.051 Al₂O₃
= 2 × 3.011 × Number of Al ions In 3.011 × 10²⁰
= 6.022 × 10²⁰.

KSEEB Solutions for Class 9 Science Chapter 3 Additional Questions

Question 1.
Write the symbols of the following:
a) Iron
b) lead
c) Zinc
d) Oxygen
e) Chlorine
Answer:
a) Iron = Fe
b) lead = Pb
c) Zinc = Zn
d) Oxygen = O
e) Chlorine = Cl

Question 2.
What is a molecule?
Answer:
The smallest particle of an element or a compound that is capable of independent existence and shows all the properties of that substance.

Question 3.
What is an ion?
Answer:
An ion is a charged species present in metals and non-metals.

Question 4.
What is molecular mass?
Answer:
The molecular mass of a substance is the sum of the atomic masses of all the atoms in a molecule of the substance.

Question 5.
What is a mole?
Answer:
One mole of any species (atoms, molecules, ions, or particles) is that quantity in number having a mass equal to its atomic or molecular mass in grams.

KSEEB Class 9 Science Atoms and Molecules Additional Questions and Answers

Question 1.
An element Z forms an oxide with formula Z₂O₃. What is its valency?
Answer :
Valency is 3⁺

Question 2.
Mention the elements present in (1) quick line (2) sodium hydrogen carbonate.,
Answer :
(1) Quick line (calcium oxide) (CaO) element present are calcium and oxygen.
(2) Sodium hydrogen carbonate (NaHCO₃) elements are sodium, hydrogen, hydrogen, carbon and oxygen.

Question 3.
Calculate the total number of ions in 0.585 g of sodium chloride.
Answer :
Gram formula mass of NaCl = 23 + 35-5 = 58.5 g
58.5 g of NaCl have ions = 2 × N_A
58.5 g of NaCl have ions
\(=2 \times \mathrm{N}_{\mathrm{A}} \times \frac{0.585}{58 \cdot 5}=0 \cdot 02 \times \mathrm{N}_{\mathrm{A}}\)
= 0.02 × 6.022 x 10²³
= 1.20 × 10²² ions