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NCERT solutions for Class 9 Science chapter 3 - Atoms and Molecules

Chapter 3 - Atoms and Molecules

Page 33

Q 1 | Page 33

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

Q 2 | Page 33

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?

Q 3 | Page 33

Which postulate of Dalton’s atomic theory is the result of the law of conservation of mass?

Q 4 | Page 33

Which postulate of Dalton’s atomic theory can explain the law of definite proportions?

Page 35

Q 1 | Page 35

Define atomic mass unit.

Q 2 | Page 35

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

Page 39

Q 1.1 | Page 39

Write down the formulae of sodium oxide.

Q 1.2 | Page 39

Write down the formulae of aluminium chloride.

Q 1.3 | Page 39

Write down the formulae of sodium sulphide.

Q 1.4 | Page 39

Write down the formulae of magnesium hydroxide.

Q 2.1 | Page 39

Write down the name of compound represented by the following formulae:- Al2(SO4)3

Q 2.2 | Page 39

Write down the name of compound represented by the following formulae:-

K2SO4

Q 2.3 | Page 39

Write down the name of compound represented by the following formulae:- CaCl2

Q 2.4 | Page 39

Write down the name of compound represented by the following formulae:-KNO3

Q 2.5 | Page 39

Write down the name of compound represented by the following formulae:- CaCO3

Q 3 | Page 39

What is meant by the term chemical formula?

Q 4.1 | Page 39

How many atoms are present in a H2S molecule?

Q 4.2 | Page 39

How many atoms are present in a PO43− ion?

Page 40

Q 1.1 | Page 40

Calculate the molecular masses of H2.

Q 1.2 | Page 40

Calculate the molecular masses of O2.

Q 1.3 | Page 40

Calculate the molecular masses of Cl2.

Q 1.4 | Page 40

Calculate the molecular masses of CO2.

Q 1.5 | Page 40

Calculate the molecular masses of CH4.

Q 1.6 | Page 40

Calculate the molecular masses of C2H6.

Q 1.7 | Page 40

Calculate the molecular masses of C2H4.

Q 1.8 | Page 40

Calculate the molecular masses of NH3.

Q 1.9 | Page 40

Calculate the molecular masses of CH3OH.

Q 2.1 | Page 40

Calculate the formula unit masses of ZnO, given atomic masses of Zn = 65 u and O = 16 u.

Q 2.2 | Page 40

Calculate the formula unit masses of Na2O, given atomic masses of Na = 23 u and O = 16 u.

Q 2.3 | Page 40

Calculate the formula unit masses of K2CO3, given atomic masses of K = 39 u, C = 12 u, and O = 16 u.

Pages 42 - 44

Q 1 | Page 43

A 0.24 g sample of compound of oxygen and boron was found by analysis to contain 0.096 g of boron and 0.144 g of oxygen. Calculate the percentage composition of the compound by weight.

Q 1 | Page 42

If one mole of carbon atoms weighs 12 gram, what is the mass (in gram) of 1 atom of carbon?

Q 2 | Page 42

Which has more number of atoms, 100 grams of sodium or 100 grams of iron (given, atomic mass of Na = 23 u, Fe = 56 u)?

Q 2 | Page 43

When 3.0 g of carbon is burnt in 8.00 g 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 50.00 g of oxygen? Which law of chemical combinations will govern your answer?

Q 3 | Page 44

What are polyatomic ions? Give examples?

Q 4.1 | Page 44

Write the chemical formulae of the Magnesium chloride.

Q 4.2 | Page 44

Write the chemical formulae of the Calcium oxide.

Q 4.3 | Page 44

Write the chemical formulae of the Copper nitrate.

Q 4.5 | Page 44

Write the chemical formulae of the Calcium carbonate.

Q 5.1 | Page 44

Give the names of the elements present in the following compound: Quick lime

Q 5.2 | Page 44

Give the names of the elements present in the following compound: Hydrogen bromide

Q 5.3 | Page 44

Give the names of the elements present in the following compound: Baking powder

Q 5.4 | Page 44

Give the names of the elements present in the following compound: Potassium sulphate

Q 6.1 | Page 44

Calculate the molar mass of the following substance: Ethyne, C2H2

Q 6.2 | Page 44

Calculate the molar mass of the following substance

Phosphorus molecule, P4 (atomic mass of phosphorus = 31)

Q 6.3 | Page 44

Calculate the molar mass of the following substance: Sulphur molecule, S8

Q 6.4 | Page 44

Calculate the molar mass of the following substance: Hydrochloric acid, HCl

Q 6.5 | Page 44

Calculate the molar mass of the following substance: Nitric acid, HNO3

Q 7.1 | Page 44

What is the mass of 1 mole of nitrogen atoms?

Q 7.2 | Page 44

What is the mass of 4 moles of aluminium atoms (Atomic mass of aluminium = 27)?

Q 7.3 | Page 44

What is the mass of 10 moles of sodium sulphite (Na2SO3)?

Q 8.1 | Page 44

Convert into mole.

12 g of oxygen gas

Q 8.2 | Page 44

Convert into mole.

20 g of water

Q 8.3 | Page 44

Convert into mole.

22 g of carbon dioxide

Q 9.1 | Page 44

What is the mass of 0.2 mole of oxygen atoms?

Q 9.2 | Page 44

What is the mass of 0.5 mole of water molecules?

Q 10 | Page 44

Calculate the number of molecules of sulphur (S8) present in 16 g of solid sulphur.

Q 11 | Page 44

Calculate the number of aluminium ions present in 0.051 g 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)

Extra questions

The average atomic mass of a sample of an element X is 16.2 u. What are the percentages of isotopes ""_8^16X" and """_8^18X  in the sample?

If bromine atom is available in the form of, say, two isotopes ""_35^79Br (49.7%)" and """_35^81Br (50.3%), calculate the average atomic mass of bromine atom.

NCERT solutions for Class 9 Science chapter 3 - Atoms and Molecules

NCERT solutions for Class 9 Science chapter 3 (Atoms and Molecules) include all questions with solution and detail explanation from Science Textbook for Class 9. This will clear students doubts about any question and improve application skills while preparing for board exams. The detailed, step-by-step solutions will help you understand the concepts better and clear your confusions, if any. Shaalaa.com has created the CBSE Science Textbook for Class 9 solutions in a manner that help students grasp basic concepts better and faster.

Further, we at shaalaa.com are providing such solutions so that students can prepare for written exams. These NCERT textbook solutions can be a core help for self-study and acts as a perfect self-help guidance for students.

Concepts covered in Class 9 Science chapter 3 Atoms and Molecules are Concept of Ion, Molecules of Compounds, Molecules of Elements, Concept of Molecule, Atomic Mass, Modern Day Symbols of Atoms of Different Elements, Concept of Atom, Law of Constant Proportions, Law of Conservation of Mass, Atoms and Molecules Introduction, Atoms and Molecules Numericals, Mole Concept, Formula Unit Mass, Molecular Mass, Writing Chemical Formulae - Formulae of Simple Compounds.

Using NCERT solutions for Class 9 Science by students are an easy way to prepare for the exams, as they involve solutions arranged chapter-wise also page wise. The questions involved in NCERT Solutions are important questions that can be asked in the final exam. Maximum students of CBSE Class 9 prefer NCERT Textbook Solutions to score more in exam.

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