9TH Class Chemistry Chapter - 1 Fundamentals of Chemistry ( SOLVED EXERCISE )

 Chapter - 1

Fundamentals of Chemistry

EXERCISE

 

Multiple Choice Questions

Put a (✓) on the correct answer

            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

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

(a)    mixture    ✓

(b)   element

(c)    compound

(d)   radical

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

(a)    oxygen    ✓

(b)   hydrogen

(c)    nitrogen

(d)   silicon

4. Which one of the following elements is found in most abundance in the Earth’s crust?

(a)   oxygen    ✓

(b)   aluminium

(c)    silicon

(d)   iron

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

(a)    Carbon monoxide

(b)   oxygen     

(c)    nitrogen

(d)   argon    ✓

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

(a)    1.66 × 10^-24 mg

(b)   1.66 × 10^-24 g    ✓

(c)    1.66 × 10^-24 kg      

(d)   1.66 × 10^-23 g

7. Which one of the following molecule is not tri-atomic?

(a)    H₂    ✓

(b)   O₃

(c)    H₂O

(d)   CO₂

8. The mass of one molecule of water is:

(a)    18 amu    ✓

(b)   18g

(c)    18mg

(d)   18kg

9. The molar mass of H₂SO₄ is:

(a)    98 g    ✓

(b)   98 amu

(c)    9.8 g

(d)   9.8 amu

10. Which one of the following is a molecular mass of O₂ in amu?

(a)    32 amu    ✓

(b)   53.12 × 10^-24 amu

(c)    1.92 × 10^-25 amu

(d)   192.64 × 10^-25 amu

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

(a)    0.15

(b)   0.18    ✓

(c)    0.21

(d)   0.24

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

(a)    1 mole of NaCl and 1 mole of MgCl₂

(b)   1/2  mole of NaCl and 1/2  mole of MgCl₂

(c)    1/2  mole of NaCl and 1/3  mole of MgCl₂    ✓

(d)   1/3  mole of NaCl and 1/2  mole of MgCl₂

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

Short answer questions.

1. Define industrial chemistry and analytical chemistry.

Ans. Industrial Chemistry:

        The branch of chemistry that deals with the manufacturing of chemical compounds on commercial scale is called industrial chemistry. It deals with the manufacturing of basic chemicals such as oxygen, chlorine, ammonia, caustic soda, nitric acid and sulphuric acid.

        Analytical Chemistry:

        Analytical chemistry is the branch of chemistry that deals with separation and analysis of a sample to identify its components. The separation is carried out prior to qualitative and quantitative analysis. This branch covers food, water, environmental and clinical analysis.

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

Ans.

Organic Chemistry	Inorganic Chemistry
Organic chemistry is the study of covalent compounds of carbon and hydrogen (hydrocarbons) and their derivatives.	Inorganic chemistry deals with the study of all elements and their compounds except those of compounds of carbon and hydrogen (hydrocarbons) and their derivatives.
This branch covers petroleum, petrochemicals and pharmaceutical industries.	This branch covers the chemical industry such as glass, cement, ceramics and metallurgy (extraction of metals from ores).

3. Give the scope of biochemistry.

Ans. Scope of biochemistry:

        It is the branch of chemistry in which we study the structure, composition, and chemical reactions of substances found in living organisms. It covers all chemical processes taking place in living organisms, such as synthesis and metabolism of biomolecules like carbohydrates, proteins and fats. Examples of applications of biochemistry are in the fields of medicine, food science and agriculture, etc.

4. How does homogeneous mixture differ from heterogeneous mixture?

Ans.

Homogeneous Mixtures	Heterogeneous Mixture
Mixtures that have uniform composition throughout are called homogeneous mixtures.	Mixtures that have not uniform composition throughout are called heterogeneous mixtures.
For  example: air, gasoline, ice cream, etc.	For example: soil, rock, wood, etc.

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

Ans. Relative atomic mass:

        The relative atomic mass of an element is the average mass of the atoms of that element as compared to 1/12^th (one-twelfth) the mass of an atom of carbon-12 isotope (an element having different mass number but same atomic number).

1 amu = 1.66 × 10^-24g

      6. Define empirical formula with an example.

      Ans. Empirical formula:

              It is defined as the formula which represents the simplest whole number ratio of atoms present in a compound. Example: Glucose has simplest ratio 1:2:1 of carbon, hydrogen and oxygen, respectively. Hence, its empirical formula is CH₂O.

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

      Ans.

Air is a mixture:

i.                    It shows the properties of its constituents.

ii.                  Its constituents can be separated by physical methods.

iii.                It does not have any chemical formula.

Water is a compound:

i.                    It shows different properties for its constitutes.

ii.                  Its constituents cannot be separated by physical methods.

iii.                It has fixed chemical formula H₂O

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

Ans. Hydrogen and oxygen are same type of atoms while water is formed by chemical reaction of hydrogen and oxygen so it is a compound.

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

Ans. Symbol is the identification used for the chemical name of the element. It represents the only one atom of the element. Symbolic representation is abbreviation for the name of element. It is easy to use symbols in chemical formulas and reactions.

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

Ans.

Soft drink is a mixture:

i.                    It shows the properties of its constituents.

ii.                  Its constituents can be separated by physical methods.

iii.                It does not have any chemical formula.

Water is a compound:

i.                    It shows different properties for its constitutes.

ii.                  Its constituents cannot be separated by physical methods.

iii.                It has fixed chemical formula H₂O.

11. Classify the following into element, compound or mixture:

i.                    He and H₂

ii.                  CO and Co

iii.                Water and milk

iv.                Gold and brass

v.                  Iron and steel

Ans.

Element	Compound	Mixture
He, Co, Gold and Iron.	H2, CO, Water.	Milk, Brass and Steel.

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

Ans. The unit used for relative atomic masses is called atomic mass unit. It is represented by amu.

1 amu = 1.66 × 10^-24g

Need: For very small particles ‘amu’ is used rather than ‘g’ or ‘kg’ because it is convenient to measure masses of such small particles like electrons, protons and neutrons.

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

i.                    Zinc + Copper

ii.                  Water + Sugar

iii.                Aluminium + Sulphur

iv.                Iron + Chromium + Nickel

Ans.

Substance	Nature	Name
Zinc + Copper	Alloy (mixture)	Brass
Water + Sugar	Solution (mixture)	Aqueous solution of sugar
Aluminium + Sulphur	Compound	Aluminium sulphide
Iron + Chromium + Nickel	Alloy (mixture)	Nichrome

14. Differentiate between molecular mass and formula mass, which of the followings have molecular formula?

H₂O, NaCl, KI, H₂SO₄

Ans.

        Molecular Mass: The sum of atomic masses of all the atoms present in one molecule of a molecular substance is called as molecular mass. For example: molecular mass of chlorine (Cl₂) is 71.0 amu, molecular mass of water (H₂O) is 18 amu, and molecular mass of carbon oxide (CO₂) is 44 amu.

        Formula Mass: The sum of atomic masses of all the atoms present in one formula unit of a substance is called formula mass. For example: formula mass of sodium chloride is 58.5 amu and formula mass of CaCO₃ is 100 amu.

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

Ans. 10g of Al has more atoms than 10g of Fe.

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

Ans. 9g of water has more molecules than 9g of sugar (C₁₂H₂₂O₁₁).

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

Ans. 1g of NaCl has more formula units than 1g of KCl.

18. Differentiate between homoatomic and heteroatomic molecules with examples.

Ans.

Homoatomic Molecule	Heteroatomic Molecule
A molecule containing same type of atoms, is called homoatomic molecule.	A molecule consists of different kinds of atoms, it is called heteroatomic molecule.
For example: hydrogen (H2), ozone (O3), sulphur (S8) and phosphorus (P4), etc.	For example: CO2, H2O and NH3, etc.

19. In which one of the followings the number o hydrogen atoms is 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).

Ans.

No. of moles of hydrogen in 1 mole of HCl = 1 mole

No. of moles of hydrogen in 2 mole of HCl = 2 moles

Whereas no. of moles of hydrogen in 1 mole of NH₃ = 3 moles

Hence 1 mole of NH₃ contains 3 moles of hydrogen and will have more hydrogen atoms than 2 moles of hydrogen present in 2 moles of HCl.