These atoms and molecules ncert solutions help students understand the fundamental concepts in a simple and clear way. They also help students to develop a strong understanding of this chapter. Some of the main things that students learn are given below:
NCERT Solutions for Class 9 Science Chapter 3 Atoms and Molecules
Have you ever wondered how things around us are made? Like the air we breathe, the phone we are currently using to read this article, or the food we eat daily to quench our appetite. The answer to all these questions lies in atoms and molecules ncert solutions. Everything in our environment, from the tiniest grain of sand to the vast universe, is made up of atoms and molecules. Atoms are the smallest unit of matter, while molecules are made up of a combination of two or more atoms, and they are so small that we cannot see them with the naked eye; to see them, we require a high-end microscope. Even a small drop of water contains countless molecules.
This Story also Contains
- Download PDF of NCERT Solutions for Class 9 Science Chapter 3
- NCERT Solutions for Class 9 Science Chapter 3 (In-text Exercise Questions)
- NCERT Solutions Class 9 Science Chapter 3( Exercise Questions with Answers)
- Practice Questions for Class 9 Science Chapter 3
- Approach to Solve Questions of Class 9 Science Chapter 3
- Topics and Subtopics Covered in the NCERT Textbook
- NCERT Class 9 Science Chapter 3: Overview
- What Students Learn from NCERT Solutions for Class 9 Science Chapter 3
- Importance of Class 9 Science Chapter 3 Atoms and Molecules Solution
- NCERT Solutions for Class 9 Science- Chapter Wise
- NCERT Books and NCERT Syllabus
The important topics like laws of chemical combinations, chemical formulas, and molecular mass are all discussed in this chapter. The NCERT Solutions for Class 9 Science will offer a very comprehensive and systematic way to present topics discussed in class 9 science chapter 3 atoms and molecules question answer through a series of solved questions. These NCERT solutions provide clear and detailed explanations that will help you understand the topics in depth. The practice questions are also included in this article to improve your problem-solving skills. We have also added some points that will help you build a good approach for solving the questions.
Download PDF of NCERT Solutions for Class 9 Science Chapter 3
Students can download the NCERT Solutions for Class 9 Science Chapter 3 Atoms and Molecules pdf from the link below and can revise the concepts anytime. These solutions of NCERT make it easier for students to understand the basic concepts of atoms, molecules, and their combinations through clear explanations.
Also read
NCERT Solutions for Class 9 Science Chapter 3 (In-text Exercise Questions)
Given below the class 9 science chapter 3 atoms and molecules solutions of in-text questions. These solutions help students understanding the fundamental concepts they also make it easy for students to quickly revise important topics before exams.
Exercise-3.1 (Page: 27)
sodium carbonate + acetic acid → sodium acetate + carbon dioxide + water
Answer:
Given the reaction
sodium carbonate + acetic acid → sodium acetate + carbon dioxide + water
Mass of sodium carbonate = 5.3g
Mass of acetic acid = 6g
Mass of sodium acetate = 8.2g
Mass of carbon dioxide = 2.2g
Mass of water = 0.9g
Now,
Total Mass on the Left Hand Side = 5.3g + 6g = 11.3g
Total Mass on the Right Hand Side = 8.2g + 2.2g + 0.9g = 11.3g
As Mass on the LHS is equal to the RHS, the observation is in agreement with the law of conservation of mass.
Answer:
Given:
Hydrogen and oxygen combine in the ratio of 1:8 by mass to form water.
Now,
For every 1 g of Hydrogen, 8 g of oxygen is needed for the reaction to take place.
Therefore, for 3 g of Hydrogen, the mass of oxygen needed = 8 $\times$ 3 = 24 g.
Hence, 24 g of Oxygen is needed to complete a reaction with 3 g of Hydrogen.
Question.3 Which postulate of Dalton’s atomic theory is the result of the law of conservation of mass?
Answer:
The postulate of Dalton’s atomic theory, which is the result of the law of conservation of mass is
"Atoms can neither be created nor destroyed".
Question.4 Which postulate of Dalton’s atomic theory can explain the law of definite proportions?
Answer:
The postulate of Dalton’s atomic theory can explain the law of definite proportions is
"The relative number and kinds of atoms are equal in given compounds."
Exercise-3.2 (Page: 30)
Question 1. Define the atomic mass unit.
Answer:
An atomic mass unit is a unit of mass used to express the weight of subatomic particles, where one unit is equal to exactly one-twelfth the mass of a carbon-12 atom.
Question 2. Why is it not possible to see an atom with naked eyes?
Answer:
We can't see the atom with the naked eye because they are minuscule in nature. They are measured in nanometres. Also, except for noble gases, all atoms do not exist independently. They exist in the form of any compound.
Exercise 3.3 and 3.4 (Page: 34)
Question 1. Write down the formulae of
(i) sodium oxide
(ii) aluminium chloride
(iii) sodium sulphide
(iv) magnesium hydroxide
Answer:
The formulas of the given compounds are :
(i) sodium oxide :
$\Rightarrow Na_2O$
(ii) aluminium chloride:
$\Rightarrow AlCl_3$
(iii) sodium sulphide:
$\Rightarrow Na_2S$
(iv) magnesium hydroxide:
$\Rightarrow Mg(OH)_2$
Question 2. Write down the names of compounds represented by the following formulae:
(i) $Al_{2}(SO_{4})_{3}$
(ii) $CaCl_{2}$
(iii) $K_{2}SO_{4}$
(iv) $KNO_{3}$
(v) $CaCO_{3}$
Answer:
The Names of the following compounds are :
(i) $Al_{2}(SO_{4})_{3}$
=Aluminium Sulphate
(ii) $CaCl_{2}$
=Calcium Chloride
(iii) $K_{2}SO_{4}$
= Potassium Sulphate
(iv) $KNO_{3}$
= Potassium Nitrate
(v) $CaCO_{3}$
= Calcium Carbonate.
Question 3. What is meant by the term chemical formula?
Answer:
The chemical formula of a compound is a symbolic representation of its composition. For example, the chemical formula for common salt is NaCl, as it is made up of Sodium (Na) and Chlorine (Cl).
Q 4.(i) How many atoms are present in a
- $H_{2}S$ molecule
Answer:
$H_{2}S$ molecule has 2 atoms of Hydrogen and 1 atom of Sulphur.
and hence,
A total of 3 atoms are present in $H_{2}S$ molecule.
Question 4.(ii) How many atoms are present in a
- $PO_{4}^{3-}$ ion?
Answer:
$PO_{4}^{3-}$ ion has one atom of Phosphorus and 4 atoms of Oxygen.
And hence,
A total of 5 atoms are present in $PO_{4}^{3-}$ ion.
Exercise-3.5.1-3.5.2 (Page: 35)
Answer:
The molecular mass of $H_2$ :
= 2 $\times$Atomic mass of Hydrogen
= 2 $\times$1u
=2u.
The molecular mass of $O_2$ :
= 2 $\times$ Atomic mass of Oxygen
= 2 $\times$16u
= 32u.
The molecular mass of $Cl_2$ :
= 2 $\times$ Atomic mass of Chlorine
= 2 $\times$ 35.5uu
= 71u.
The molecular mass of $CO_2$ :
= Atomic mass of Carbon +2 $\times$ Atomic mass of Oxygen
= 12u + 2 $\times$16u
= 44u.
The molecular mass of $CH_4$ :
= Atomic mass of Carbon +4 $\times$Atomic mass of Hydrogen
= 12u + 4 $\times$1u
= 16u.
The molecular mass of $C_2H_6$ :
= 2 $\times$ Atomic mass of Carbon + 6 $\times$ Atomic mass of Hydrogen
= 2$\times$12u+ 6 $\times$1u
=24u+ 6u
= 30u.
The molecular mass of $C_2H_4$ :
= 2 $\times$ Atomic mass of Carbon + 64$\times$Atomic mass of Hydrogen
= 2$\times$12u+ 4$\times$1u
=24u+ 4u
= 28u.
The molecular mass of $NH_3$ :
= Atomic mass of Nitrogen + 3 $\times$Atomic mass of Hydrogen
= 14u+ 3 $\times$ 1u
= 17u.
The molecular mass of $CH_3OH$ :
= Atomic mass of Carbon +4$\times$Atomic mass of Hydrogen + Atomic mass of Oxygen
= 12u+ 4 $\times$ 1u + 16u
= 32u.
Answer:
Given,
the atomic mass of Zn = 65 u,
the atomic mass of Na = 23 u,
the atomic mass of K = 39 u,
the atomic mass of C = 12 u,
and the atomic mass of O = 16 u
Now,
Formula unit mass of ZnO = Atomic mass of Zinc + Atomic mass of O
= 65 u + 16 u
= 81 u.
Formula unit mass of Na2O = 2 $\times$ Atomic mass of Na+ Atomic mass of O
= 2 $\times$23 u + 16 u
= 62 u.
Formula unit mass of K2CO3 = 2$\times$ Atomic mass of K+ Atomic mass of C + 3 $\times$ Atomic mass of O
= 2 $\times$ 39 u + 12 u + 3 $\times$ 16 u
= 138 u.
NCERT Solutions Class 9 Science Chapter 3( Exercise Questions with Answers)
These solutions provide clear answers to all the exercise questions of atoms and molecules ncert solutions. They help students to understand how to solve numerical problems and explain concepts in simple language.
Answer:
The total mass of the compound = 0.24 g
Mass of boron in the compound = 0.096 g
Mass of oxygen in the compound = 0.144 g
Now, as we know,
The percentage of an element in the compound :
$=\frac{total\:mass\:of\:element}{total\:mass\:of\:compound}\times 100$
So,
The percentage of Boron in the compound by weight :
$=\frac{0.096}{0.24}\times 100$
$=40\%$
The percentage of Oxygen in the compound by weight :
$=\frac{0.144}{0.24}\times 100$
$=60 \%$
Answer:
3.0 g of carbon combines with 8.0 g of oxygen to give 11.0 g of carbon dioxide.
So, by the law of definite proportions,
When 3.00 g of carbon is burnt in 50.00 g of oxygen, only 8.00 g of oxygen will be used to produce 11.00 g of carbon dioxide. The remaining 42.00 g of oxygen will remain unreacted. The law of constant proportion is held.
Q 3. What are polyatomic ions? Give examples.
Answer:
Polyatomic ions are ions that contain more than one atom. These atoms can be of the same type or of a different type.
Some examples of polyatomic ions are NH4+ , OH- , SO42- , and SO32- .
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:
The chemical formula of the given compounds is:
(a) Magnesium chloride
$=MgCl_2$
(b) Calcium oxide
$=CaO$
(c) Copper nitrate
$=Cu(NO_3)_2$
(d) Aluminium chloride
$=AlCl_3$
(e) Calcium carbonate
$=CaCO_3$
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:
The names of the elements present in the given compounds are :
(a) Quick lime :
$CaO$ = Calcium and Oxygen.
(b) Hydrogen bromide:
$HBr$ = Hydrogen and Bromine.
(c) Baking powder:
$NaHCO_3$ = Sodium, Hydrogen, Carbon, and Oxygen.
(d) Potassium sulphate:
$K_2SO_4$ = Potassium, Sulphur, and oxygen.
Question 6.(a) Calculate the molar mass of the following substances.
- Ethylene , $C_{2}H_{2}$
Answer:
The molecular mass of ethyne, $C_{2}H_{2}$ = 2 $\times$Atomic Mass of C + 2 $\times$ Atomic Mass of H
= 2 $\times$ 12u + 2 $\times$ 1u
= 24u + 2u
= 26u
Question 6. (b) Calculate the molar mass of the following substances.
- Sulphur molecule, S8
Answer:
The molecular mass of Sulphur molecule, = 8 $\times$ Atomic Mass of S
= 8 $\times$ 32u
= 256u
Question 6.(c) Calculate the molar mass of the following substances
- Baking soda
Answer:
The molecular formula of Baking soda is NaHCO3
So the molecular mass will be some of the individual atoms involved in the formula.
Molecular Mass of baking soda = Molecular mass (Na + H + C + 3xO)
= 23 + 1 + 12 + 3x16
= 84 g/mol
Question 6.(d) Calculate the molar mass of the following substances.
- Hydrochloric acid, HCl
Answer:
The molecular mass of Hydrochloric acid, HCl = 1 $\times$ Atomic Mass of Cl + 1 $\times$ Atomic Mass of H
= 35.5 u + 1u
= 36.5u
Question 6. (e) Calculate the molar mass of the following substances.
- Nitric acid, HNO3
Answer:
The molecular mass of Nitric acid, HNO3 = 1 $\times$ Atomic Mass of N + 1 $\times$ Atomic Mass of H + 3 $\times$ Atomic Mass of O
= 1$\times$ 14u + 1 $\times$1u + 3 $\times$ 16u
= 14u + 1u + 48u
= 63u
Practice Questions for Class 9 Science Chapter 3
The class 9 science chapter 3 atoms and molecules question answer are given below for practice. These practice questions are designed to test students understanding of the basic concepts.
Question 1. State the Law of Conservation of Mass.
Answer:
The Law of Conservation of Mass states that mass can neither be created nor destroyed in a chemical reaction. The total mass of reactants is equal to the total mass of products.
Question 2. What is the chemical formula of water and carbon dioxide? Name the elements present in them.
Answer:
Water $\left(\mathrm{H}_2 \mathrm{O}\right)$; Elements – Hydrogen and Oxygen
Carbon dioxide $\left(\mathrm{CO}_2\right)$; Elements – Carbon and Oxygen
Question 3. Define atomicity. Give the atomicity of oxygen $\left(\mathrm{O}_2\right)$ and phosphorus ($\mathrm{P}_4$).
Answer:
Atomicity is the number of atoms present in a molecule of an element.
Oxygen $\left(\mathrm{O}_2\right)$; Diatomic (Atomicity = 2)
Phosphorus ($\mathrm{P}_4$); Tetratomic (Atomicity = 4)
Question 4. Calculate the molecular mass of carbon dioxide ($\mathrm{CO}_2$).
(1) 44
(2) 45
(3) 43
(4) 42
Answer:
Atomic mass of C = 12 u, O = 16 u
Molecular mass of $\mathrm{CO}_2$ = 12 + (16 × 2) = 44 u
Hence, the correct answer is option (1).
Question 5. What is meant by a mole? How many particles are there in one mole of a substance?
Answer:
A mole is the amount of a substance that contains $6.022 \times 10^{23}$ particles. This number is called Avogadro’s constant.
Question 6: An atom of some element Y weighs $6.644 \times 10^{-23}$ g. Calculate the number of gram-atoms in 40 kg of it.
(1) 1200
(2) 100
(3) 1000
(4) 1100
Answer:
Mass of 1 mole Y atoms
= mass of 1 atom x Avogadro constant
=$6.644 \times 10^{-23} \times 6.022 \times 10^{23}$
= 40 g
So, the atomic mass of Y = 40
No. of gram-atoms (or moles) of X = (mass of y)/(atomic mass)
Number of gram atoms $=\frac{40 \times 1000}{40}$
Thus, the number of gram atoms = 1000 atoms
Hence, the answer is the option (3).
Question 7: How many atoms of hydrogen are there in 36 g of $\mathrm{NH}_4$?
(1) $9.635 \times 10^{23}$ atoms
(2) $96.35 \times 10^{24}$ atoms
(3) $4.81 \times 10^{23}$ atoms
(4) $48.17 \times 10^{23}$ atoms
Answer:
Molar mass (Molecular mass in gram) of $\mathrm{NH}_4$ = 14+4= 18 g
No. of moles of $\mathrm{NH}_4$ = 36/18 = 2 moles
Now, total moles of hydrogen atoms in one mole of $\mathrm{NH}_4$ = 4 moles
Thus, total Moles of Hydrogen Atoms in 2 moles of $\mathrm{NH}_4$ = 2 x 4 = 8 moles
Now, we know that in 1 mole of hydrogen atoms, the number of hydrogen atoms = $6.022 \times 10^{23}$
Thus, in 8 moles of hydrogen atoms, the number of atoms present = $8 \times 6.022 \times 10^{23}$
= $48.17 \times 10^{23}$ atoms
Hence, the answer is the option (4).
Question 8: Calculate the molar mass of CaCOH.
(1) 67g
(2) 72g
(3) 69g
(4) 70g
Answer:
The atomic mass of the consisting elements are:
Ca = 40u
C = 12u
O = 16u
H = 1u
Now, the molecular mass of CaCOH is given as:
Molecular mass = 40 + 12 + 16 + 1
Molecular mass = 69u
Thus, the molar mass of CaCOH = 69g
Hence, the answer is the option (3).
Approach to Solve Questions of Class 9 Science Chapter 3
Students can follow the approaches given below to solve atoms and molecules class 9 question answer. Referring to these NCERT Solutions for Class 9 will also help in understanding the correct methods. Follow the points below to make a good strategy for solving questions from this chapter:
1. Understand the structure of this chapters and break the chapter into manageable sections.
2. After that, try to learn and memorize key concepts of the chapter, such as Dalton’s Atomic Theory, the Law of Conservation of Mass, features of atomic and molecular masses, the mole concept, and molar mass, etc.
3. Write all the definitions on a separate sheet to solve definition based questions. Make a formula sheet related to the mole concept and molar masses to effectively solve numerical. You can also learn the topics from atoms and molecules class 9 notes available on our website.
4. Solve the NCERT examples and practice with in-text questions. Also, use some common tricks, like unit conversion, memorize symbols, and valency. Practice as many questions as asked in previous board exams and solve mock tests. Follow the class 9 science chapter 3 atoms and molecules solutions to learn more.
Topics and Subtopics Covered in the NCERT Textbook
All the topics and subtopics covered in atoms and molecules class 9 question answer are listed below. This helps students to get a clear overview of the chapter and focus on each concept clearly:
3.1 Laws of Chemical Combination
3.1.1 Law of Conservation of Mass
3.1.2 Law of Constant Proportions.
3.2 What is an Atom?
3.2.1 What Are the Modern-Day Symbols of Atoms of Different Elements?
3.2.2 Atomic Mass
3.2.3 How do Atoms exist
3.3 What is a Molecule?
3.3.1 Molecules of Elements
3.3.2 Molecules of Compounds
3.3.3 What is An Ion?
3.4 Writing Chemical Formulae
3.4.1 Formulae of Simple Compounds
3.5 Molecular Mass
3.5.1 Formula Unit Mass
NCERT Class 9 Science Chapter 3: Overview
This chapter provides students with the basic concepts of atoms and molecules, the building blocks of matter. It begins with Dalton’s Atomic Theory, which explains the nature of atoms and their behavior. Students will learn about the laws of chemical combination; Law of Conservation of Mass and the Law of Constant Proportions. NCERT Solutions for Class 9 Science Chapter 3 Atoms and Molecules will explain to you what atoms, molecules, and ions are and how they form compounds. It will also feature atomic and molecular masses, chemical formulas and how to calculate the mole and molar mass using the concept of the Avogadro number. This chapter will help you understand chemical reactions and formulas.
What Students Learn from NCERT Solutions for Class 9 Science Chapter 3
-
These solutions help students to understand the basic concepts of atoms and molecules such as structure of atoms, how they combine to form molecules and the laws of chemical combination.
-
Here chemical formulas and reactions are well explained.
-
Using these class 9 science chapter 3 atoms and molecules solutions they learn how to write chemical formulas of compounds and how molecules participate in chemical reactions.
-
Calculation of molar mass, molecular mass are explaned will in these solutions through a series of solved questions.
-
Understand the concept of the mole and its importance in chemistry are explained well in these solution.
Importance of Class 9 Science Chapter 3 Atoms and Molecules Solution
The class 9 science atoms and molecules question answer help students understanding concepts and improve their problem solving skills. Given below are some points on why these solutions are important:
1. The solutions explain concepts like atoms, molecules, laws of chemical combination, and atomic mass.
2. It helps to develop a base for topics like chemical reactions and equations in higher classes.
3. These atoms and molecules class 9 question answer help students in solving mole concept and mass calculation questions accurately.
4. They provide detailed solutions that help students in writing precise answers.
NCERT Solutions for Class 9 Science- Chapter Wise
Along with NCERT Solutions for Class 9 Science Chapter 3 Atoms and Molecules students can also follow other chapters of class 9 NCERT solutions links:
NCERT Books and NCERT Syllabus
Follow the links below to get the syllabus and prescribed books. Learn more from the atoms and molecules class 9 science NCERT notes.
Frequently Asked Questions (FAQs)
Q: What is NCERT Solutions for Class 9 Science Chapter 3 Atoms and Molecules?
A:
Class 9 Science Chapter 3 NCERT Solutions provide detailed answers to all questions in the textbook. They help students understand the concepts of atoms, molecules, chemical formulas, and laws of chemical combination clearly.
Q: What is Chapter 3 science class 9?
A:
Chapter 3 of Class 9 Science is titled Atoms and Molecules. It explains the basic structure of atoms, how atoms combine to form molecules, and the laws of chemical combination.
Q: What is the difference between atoms and molecules in NCERT?
A:
In NCERT, atoms are the smallest units of an element that retain its identity, while molecules are formed when two or more atoms combine chemically. Atoms are the building blocks, and molecules are combinations of these atoms.
Q: What are Ions as discussed in class 9 NCERT solutions? How are they formed?
A:
Ions are charged particles. They are formed when an atom gains or loses electrons.
- Cation- A positively charged ion formed when an atom loses one or more electrons.
- Anion- A negatively charged ion formed when an atom gains one or more electrons.
Q: What are chemical bonds and why do atoms form them?
A:
Chemical bonds are attractive forces that hold atoms together in molecules and compounds. Atoms form chemical bonds to achieve a more stable electron configuration.
Q: What is a chemical formula?
A:
A chemical formula is a way of expressing information about the atoms that constitute a particular chemical compound. It provides the types and numbers of atoms present in the molecule.
Q: Why is it important to study class 9 science atoms and molecules question answer?
A:
Studying atoms and molecules is important because they are the foundation of all matter. Understanding their structure and interactions helps us grasp chemical reactions, the properties of substances, and the principles behind various scientific and industrial processes.
Q: What is the law of conservation of mass?
A:
The law of conservation of mass states that mass can neither be created nor destroyed in a chemical reaction. This means that the total mass of reactants must equal the total mass of products.
Q: What are the types of chemical bonds mentioned in the class 9 science atoms and molecules question answer?
A:
The class 9 science chapter 3 atoms and molecules question answer discusses two main types of chemical bonds: ionic bonds and covalent bonds. Ionic bonds occur when electrons are transferred from one atom to another, resulting in charged ions that attract each other. Covalent bonds form when two atoms share electrons, creating a strong link between them.
Q: What are the key topics covered in the class 9 science chapter 3 atoms and molecules solutions?
A:
The NCERT Solutions for Chapter 3 cover topics such as the structure of atoms, the difference between atoms and molecules, the laws of chemical combination, types of molecules, and the concept of molecular mass. Each solution is designed to clarify concepts and provide practice problems for better understanding.
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