Chemistry 9th Chapter 1 Fundamentals of Chemistry Exercise Short Question

Chemistry 9th Chapter 1 Fundamentals of Chemistry Exercise Short Question

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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, s called industrial chemistry. It deals with the manufacturing of fertilizers, textile, soap, agricultural products, paints, paper etc.

Analytical Chemistry: It is the branch of chemistry which deals with the separation and analysis of a sample to identify its components. The separation is carried out prior to qualitative and quantitative analysis. Different techniques and instruments used for analysis are also studied in this branch.

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

Ans. Organic Chemistry: Organic chemistry is the study of covalent compounds of carbon and hydrogen (hydrocarbons) and their derivatives.

Inorganic Chemistry: Inorganic chemistry deals with the study of all elements and their compounds except those of compounds of carbon and hydrogen (hydrocarbons) and their derivatives.

3. Give the scope of biochemistry.

Ans. The scope of biochemistry is very vast, Its applications are in the fields of medicines, food science and agriculture etc.

4. How does homogeneous mixture differ from heterogeneous mixture?

Ans. Homogenous Mixture: Mixtures having uniform composition throughout are called homogeneous mixtures e.g. air, ice cream.

Heterogeneous Mixture: Heterogeneous mixtures is that in which composition is not uniform throughout e.g. soil, rock.

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

Ans. The relative atomic mass of an element is the average mass of atoms of that element as compared to 1/12th the mass of one atom of carbon-12 isotope. Its unit is called atomic mass unit with symbol ‘amu’. One atomic mass unit is 1/12th the mass of one atom of carbon-12th. When this atomic mass unit is expressed in grams, it is equivalent to:

1 amu = 1.66 x 10(-24) g

6. Define empirical formula with an example.

Ans. The type of formula which shows the simplest whole number ratio of atoms present in a compound is called empirical formula. e.g. glucose (C6H12O6) has simplest ration 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. i) Water is a compound because it is formed by chemical combination of hydrogen and oxygen whereas air is formed by simple mixing of different gases.

ii) Water has fixed ration between masses of hydrogen and oxygen, whereas in air ratio between masses of component gases is not fixed.

iii) Water has definite melting and boiling points whereas air does not have any fixed melting and boiling point.

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

Ans. Hydrogen and oxygen are elements because in these substances same type of atoms with same atomic number are present whereas water is made up of hydrogen and oxygen atoms having different atomic numbers. Hydrogen and oxygen cannot be decomposed into simpler substances by chemical means whereas water can be decomposed into hydrogen and oxygen by electrolysis.

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

Ans. Symbol is the international recognition of an element. With the help of symbol scientists form the formulae of different compounds. Symbol also helps to write and understand chemical reactions. The periodic table is based on symbols of different elements. We should say without symbols Chemistry would mot be easy to understand.

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

Ans. Soft drink (Cold drink) is a true solution of sugar and water in which CO2 is dissolved through pressure. We can separate these compounds by physical methods. It does not have definite melting and boiling point. Therefore cold drink is a mixture whereas water is formed by chemical combination of hydrogen and oxygen.

2H2O + O2 ------> 2H2O

We cannot separate these two gases by physical methods. It has definite freezing and boiling points. Therefore water is a compound.

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

i. He and H ii. CO and Co iii. Water and milk iv. Gold and brass v. Iron and steel

Ans. Element: He, Co, Gold and Iron

Compound: H2, CO and Water

Mixture: Milk, Brass and Steel

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

Ans. The unit for relative atomic mass is called atomic mass unit. Its symbol is “amu”. One atomic mass unit is 1/12th the mass of one atom of carbon-12th. The mass of an atom is too small to be determined practically. So to determine the atomic mass of various elements atomic mass unit is needed.

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 molecular mass. e.g. molecular mass of water is 18amu. Whereas Formula mass is the sum of atomic masses of all atoms present in one formula unit of a substance is called formula mass. e.g. formula mass of sodium chloride is 58.5 amu. H20 and H2SO4 are molecular formulae of molecular compounds water and sulphuric acid respectively.

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

Ans. i) Given mass of Al = 10g

Molar mass of Al = 27gmol-1

No. of atoms in 10g of Al = No. of moles x NA

No. of atoms in 10g of Al = (Given Mass)/(Molar Mass) x NA

No. of atoms in 10g of Al = 10g / (27g/mol) x 6.02 x 10(23) atoms

No. of atoms in 10g of Al = 2.23 x 10(23) atoms

ii) Given mass of Fe = 10g

Molar mass of Fe = 56gmol-1

No. of atoms in 10g of Fe = 10g / (56g/mol ) x 6.02 x 10(23) atoms

No. of atoms in 10g of Fe = 1.115 x 10(23) atoms

Therefore 10g of Al contains more atoms as compared to 10g of Fe.

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

Ans. i) Given mass of water (H2O) = 9g

Molar mass of water (H2O)= 18gmol-1

No. of molecules in 9g of water (H2O) = (Given Mass)/(Molar Mass) x NA

No. of molecules in 9g of water (H2O) = 9g / (18g/mol ) x 6.02 x 10(23) molecules

No. of molecules in 9g of water (H2O) = 3.01 x 10(23) atoms

ii) Given mass of Sugar (C12H22O11) = 9g

Molar mass of Sugar (C12H22O11) = 342gmol-1

No. of molecules in 9g of Sugar (C12H22O11) = 9g / (342g/mol ) x 6.02 x 10(23) molecules

No. of molecules in 9g of Sugar (C12H22O11) = 1.584 x 10(22) molecules

Therefore, 9g of water contains more molecules than 9g of sugar.

17. Which one has more formula units: 1 g of NaCl or 1 g of KC1?

Ans. i) Given mass of NaCl = 1g

Formula mass of NaCl = 58.5gmol-1

No. of formula units in 1g of NaCl = (Given Mass)/(Molar Mass) x NA

No. of formula units in 1g of NaCl = 1g / (58.5g/mol ) x 6.02 x 10(23) formula units (particles)

No. of formula units in 1g of NaCl = 1.029 x 10(22) formula units (particles)

ii) Given mass of KCl = 1g

Formula mass of KCl = 74.5gmol-1

No. of formula units in 1g of KCl = 1g / (74.5g/mol ) x 6.02 x 10(23) formula units (particles)

No. of formula units in 1g of KCl = 8.080 x 10(21) formula units (particles)

Therefore, 1g of NaCl contains more formula units than 1g of KCl.

18. Differentiate between homoatomic and heteroatomic molecules with examples.

Ans. Homoatomic molecules: A molecule containing same type of atoms is called homoatomic molecules. e.g. Hydrogen(H2), Oxygen(O2), Ozone(O3) and sulphur(S8) are homoatomic molecules.

Heteroatomic molecules: A molecule consisting of different types of atoms is called heteroatomic molecule. e.g. NH3, H2O and CO2 are heteroatomic molecules.

19. In which one of the followings the number of hydrogen atoms is more? 2 moles of HC1 or 1 mole of NH (Hint: 1 mole of a substance contains as much number 3 of moles of atoms as are in 1 molecule of a substance)

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

No. of moles of hydrogen in 2 moles 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.