Class 9th

Chemistry

Chapter 01

Fundamentals of chemistry (Exercise Solution)

Multiple choice questions

1. Industrial chemistry deals with the manufacturing of compounds:

a) in the laboratory

b) on micro scale

c) on commercial scale

d) on economic scale

Answer = c

2. Which one of the following can be separated by physical means?

a) Mixture

b) Element

c) Compound

d) Radical

Answer = a

3. The most abundant element occurring in the ocean is:

a) Oxygen

b) Hydrogen

c) Nitrogen

d) Silicon

Answer = a

4. Which of the following element is found in most abundance in the earth’s crust?

a) Oxygen

b) Aluminium

c) Nitrogen

d) Silicon

Answer = a

5. The third abundant gas found in the atmosphere is:

a) Carbon monoxide

b) Oxygen

c) Nitrogen

d) Argon

Answer = d

6. One amu (atomic mass unit) is equivalent to :

a) 66×10^-24mg

b) 66×10^-24 g

c) 66×10^-21 g

d) 66×10^-23 g

Answer = b

7. All of the following are tri-atomic molecule except:

a) H₂

b) O₃

c) H₂O

d) CO₂

Answer = a

8. The mass of one molecule of water is:

a)18amu

b) 18g

c) 18mg

d) 18kg

Answer = a

9. The molar mass of H₂SO₄ is:

a) 98g

b) 48amu

c) 8g

d) 98amu

Answer = a

10. Molar mass is usually expressed in grams. Which one of the following is molar mass of O₂ in amu?

a) 32amu

b) 2×10^-24 amu

c) .92×10^-25 amu

d) 64×10^-25amu

Answer = a

11. How many numbers of moles are equivalent to 8 grams of CO₂?

a) 15

b) 18

c) 21

d) 24

Answer = b

12. Which one of the following pairs has the same number of ions?

a) 1 mole of NaCl and 1 mole of MgCl₂

b) ½ mole of NaCl and ½  mole of MgCl₂

c) ½ mole of NaCl and 1/3 mole of MgCl₂

d) 1/3 mole of NaCl and ½ mole of MgCl₂

Answer = c

13. Which one of the following pairs has the same mass?

a) 1 mole of CO and 1 mole of N₂

b)1 mole of CO and 1 mole of CO₂

c) 1 mole of O₂ and 1 mole of N₂

d) 1 mole of O₂ and 1 mole of CO₂

Answer = a

EXERCISE SHORT QUESTIONS

1. Define industrial chemistry and analytical chemistry.

Answer:

Industrial chemistry:

The field of chemistry which deals with the production of chemical compounds on industrial scale, is known as industrial chemistry.

For example:

Some fundamental chemicals such as oxygen, chlorine, ammonia, caustic soda that act as raw materials for many other industries such as fertilizer, soap industry etc., are produced through industrial chemistry.

Analytical chemistry:

The field of chemistry that is involved in the identification of components in sample by its separation and analysis is called analytical chemistry. Generally, it consists of two types of sample separation, one is qualitative analysis and other is quantitative analysis.

2. How can you differentiate between organic and inorganic chemistry?

Answer:

3. Give the scope of biochemistry.

Answer:

Biochemistry is the field of chemistry which deals with the study of structures, chemical reactions and composition of substances that are present in living organisms. Biochemistry has vast applications in different fields like food science, agriculture, medical research and healthcare, molecular biology etc. Biochemistry has significant contribution towards understanding of DNA structures.  So biochemistry has great scope and it covers many areas.

4. How does homogenous mixture differ from heterogeneous mixture?

Answer:

5. What is the relative atomic mass? How it is related to gram?

Answer:

Relative atomic mass of an element is defined as “the average mass of an atom of an element, measured in atomic mass unit (amu), relative to one-twelfth (1/12^th) mass of a carbon-12 atom”. So the unit of relative atomic mass is amu.

Atomic mass unit:

One amu is 1/12^th the mass of one atom of carbon-12.

Here, we show atomic mass unit (amu) in grams by following relationship:

1 amu=1.66 ×10^-24 g

For example:

Mass of a proton =1.0073 amu = 1.672×10^-24 g

6. Define empirical formula with example.

Answer:

Empirical formula is the simplest type of chemical formula.

Empirical formula represents the compounds which has simplest whole number ratio of atoms.

If we know the percentage composition of a compound, then we can easily determine its empirical formula.

For example:

The ratio of Carbon, Hydrogen and Oxygen atoms in glucose molecule (C6H12O6) is 1:2:1.

So, its empirical formula is CH₂O.

7. State three reasons why do you think air is mixture and water is a compound.

Answer:

Reason 1:

Air does not have fixed melting and boiling point. On the other hand, water has definite melting and boiling point.

Reason 2:

Air is mixture because it is formed by the physical combination of different gases such as Nitrogen, Oxygen and hydrogen, etc. While, water is a compound because it is formed by the chemical combination of Oxygen and hydrogen atoms.

Reason 3:

Air does not have fixed ratio of nitrogen, oxygen, and carbon dioxide while water has fixed ratio of hydrogen and oxygen.

8. Explain why are hydrogen and oxygen considered elements whereas water as a compound.

Answer:

Hydrogen and oxygen are considered elements because they are not divided into further substances by chemical reactions and they found as an elements on periodic table because of their own unique properties. Whereas, on the other hand, water is considered as compound because it is formed by different elements that are bonded chemically. Water has a fixed composition with ratio of two hydrogen atoms and one oxygen atom in every molecule.

That’s why, Oxygen and hydrogen are elements and water is a compound.

9. What is the significance of the symbol of an element?

Answer:

The symbol of an elements has great importance in chemistry and other sciences.

Symbol represents the element universally. It helps scientist from different languages to understand easily. It provide clear and short way to remember elements for use in equation, formulas and diagrams. Symbols are used in periodic table to quickly find its properties just like its atomic number and atomic weight.

Symbols are also used in nomenclature and scientific notation for clarity and better understanding in publication.

For example:

Oxygen (O), Sulphur (S), etc.

10. State the reason: soft drink is a mixture and water is a compound.

Answer:

Soft drink is considered as a  mixture because it is made up of several different substances that are physically combined with each other. They are not combined together chemically. Water, carbon dioxide, flavourings, and other substances combined to form soft drinks. Through evaporation and filtration we can separate them by physical means.

For example:

Cola, lemon-lime drinks, root beer etc.

On the other hand, water is considered as a compound because it is made up of fixed ratio of oxygen and hydrogen. Water is made up of elements that are chemically boned with each other.

By physical means, water cannot be divided into its components. It require some chemical reaction such as electrolysis to break the bond.

Due to these reasons, soft drink is a mixture and water is a compound.

11. Classify the following into elements, compounds or mixture:

• He and H₂:

 Both He and H₂ are classified as elements.

• CO and Co:

CO (carbon monoxide) is a compound and Co (cobalt) is classified as an element.

• Water and milk:

Water is a compound and milk is classified as mixture.

• Gold and brass:

Gold is an element and brass is classified as a mixture.

• Iron and steel:

Iron is an element and steel is classified as a mixture.

12. Define atomic mass unit. Why is it needed?

Answer:

‘’Atomic mass unit is 1/12^th the mass of one atom of carbon-12. The abbreviation of atomic mass unit is amu.

Need:

Atomic mass unit is used to measure the very small masses of atom and molecules.

It provides a language that is useful for all worldwide scientists.

13. State the nature and name of the substance formed by combining the following:

• Zinc + Copper:

Nature: Zinc and copper combine to form alloy.

Name of the substance: This alloy is named as brass.

• Water+ sugar:

Nature: Water and sugar combine to form mixture.

Name of the substance: This mixture is named as syrup.

• Aluminium+ sulphur:

Nature:  Aluminium and sulphur combine to form compound.

Name of the substance: This compound is named as aluminium-sulphide.

• Iron+chromium+nickel:

Nature: it is an alloy or mixture.

Name of the substance: This alloy or mixture is named as nichrome.

14. Differentiate between molecular mass and formula mass. Which of the following have molecular formula?

H₂O, NaCl, Kl, H₂SO₄

Answer:

H₂O and H₂SO₄ have molecular formula.

15. Which one has more atoms: 10g of Al or 10g of Fe?

Answer:

To determine which one has more atoms, we have to calculate:

For Al:

Given mass of Al                         =10g

Molar mass of Al                        =27gmol^-1

So,

Number of atoms in 10g of Al= No of moles ×N_A

No. of atoms =   N_A

No. of atoms =

Number of atoms = 2.23×10²³ atoms

For Fe:

Given mass of Fe                         = 10g

Molar mass of Fe                        =56g mol^-1

So,

Number of atoms =  N_A

No. of atoms =

No. of atoms = 1.075 ×10²³ atoms

Hence, 10g of Aluminium (Al) has more number of atoms than 10g of Iron (Fe).

16. Which one has more molecules: 9g of water or 9g of sugar (C₁₂H₂₂O₁₁)?

Answer:

For water:

Given mass of water (H₂O)                  = 9 g

We know,

Molar mass of water                            =18 gmol^-1

Number of molecules in 9g of water =  N_A

No. of molecules =

No. of molecules = 3.01×10²³ molecules

For sugar:

Given mass of sugar                             = 9 g

We know,

Molar mass of sugar                           =342gmol^-1

Number of molecules in 9g of sugar =  N_A

No. of molecules =

No. of molecules = 1.548×10²³ molecules

Hence, 9g of H₂O has more molecules than 9g of sugar.

17. Which one has more formula units: 1g of NaCl or 1g of KCl?

Answer:

For NaCl:

Given mass of NaCl = 1 g

We know,

Formula mass of NaCl = 58.5gmol^-1

Formula units in 1g of NaCl =    N_A =

Formula units = 0.17 ×10²² formula units

For KCl:

Given mass of KCl = 1 g

We know,

Formula mass of KCl = 74.5g mol^-1

Formula units in 1g of KCl =    NA =

Formula units = 0.13 ×10²² formula units

Hence, 1g of NaCl has more formula units than 1g of KCl.

18. Differentiate between homoatomic and heteroatomic molecules with examples.

Answer:

19. In which one of the following the number of hydrogen atoms are more?

2 moles of HCl or 1 mole of NH₃

(Hint: 1 mole of a substance contains as much number of moles of atoms as are in 1 molecule of a substance.)

Answer:

Number of moles of hydrogen in 1 mole of HCl = 1 mole

Number of moles of hydrogen in 2 moles of HCl = 2 mole

On the other hand,

Number of moles of hydrogen in 1 mole of NH₃ = 3 moles

Therefore, 1 mole of NH₃ have more hydrogen atoms as compared to 2 moles of HCl.

Class 10th Chemistry Chapter 09 Chemical Equilibrium Exercise Solution

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