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Chapter 1 Fundamentals of Chemistry

ADNAN SOHAIL M. Phil Chemistry

1. In which branch of chemistry behaviour of gases and liquids is studied? Ans. The behaviour of gases and liquids is studied in physical chemistry

2. Define biochemistry? Ans. It is the branch of chemistry in which we study the structure, composition, and chemical reactions of substances found in living organisms.

3. Which branch of chemistry deals with preparation of paints and paper? Ans .Industrial chemistry deals with preparation of paints and paper.

4. In which branch of chemistry the metabolic processes of carbohydrates and proteins are studied? Ans .The metabolic processes of carbohydrates and proteins are studied in biochemistry

5. Which branch of chemistry deals with atomic energy and its uses in daily life? Ans .Nuclear chemistry deals with atomic energy and its uses in daily life.

6. Which branch of chemistry deals with the structure and properties of naturally occurring molecules? Organic chemistry deals with the structure and properties of naturally occurring molecules.

1. Can you identify mixture, element or compound out of the following: Coca cola, petroleum, sugar, table salt, blood, gun powder, urine, aluminium, silicon, tin, lime and ice cream? Ans.

Element aluminium, silicon, tin Compound sugar, table salt, lime Mixture Coca cola, petroleum, blood, gun powder, urine, ice cream.

2. How can you justify that air is a homogenous mixture. Identify substances present in it? Ans. Air is a homogenous mixture because it has uniform composition throughout. Air is a mixture of nitrogen, oxygen, carbon dioxide, noble gases and water vapours.

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3. Name the elements represented by the following symbols: Hg, Au, Fe, Ni, Co, W, Sn, Na, Ba, Br, Bi. Ans.

Symbol Name Hg Mercury Au Gold Fe iron Ni Nickel Co cobalt W tungsten

Sn tin Na Sodium Ba Barium Br Bromine Bi Bismith 4. Name a solid, a liquid and a gaseous element that exists at the room temperature. Ans. Solid iron (Fe), Gold (Au), Silver (Ag) Liquid Bromine (Br2) Gas Hydrogen (H2), Nitrogen (N2), oxygen (O2)

5. Which elements do the following compounds contain? Sugar, common salt, lime water and chalk.? Ans.

Compound elements Sugar Carbon, hydrogen, oxygen Common Salt Sodium, Chlorine Lime water Calcium, hydrogen, oxygen Chalk calcium, carbon, oxygen

Test yourself 1.3

1. How many amu 1 g of a substance has?

Ans. 1g of a substance has amu equal to Avogadro’s number (6.02 x 1023).

2. Is atomic mass unit a SI unit of an atomic mass? Ans. Yes, atomic mass unit is a SI unit of an atomic mass.

3. What is the relationship between atomic number and atomic mass? Ans. The relationship between atomic number (Z) and atomic mass (A) is given as:

Number of neutrons (n) = A -- Z

4. Define relative atomic mass? Ans. The relative atomic mass of an element is the average mass of the atoms of that element as compared to 1/12th (one-twelfth) the mass of an atom of carbon- 12 isotope.

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5. Why atomic mass of an atom is defined as relative atomic mass?

Ans. As we know that the mass of an atom is too small to be determined practically.

However, certain instruments enable us to determine the ratio of the atomic masses of

various elements to that of carbon-12 atoms. This ratio is known as the relative atomic mass

of the element.

Test yourself 1.4

1. What is the relationship between empirical formula and formula unit?

Ans. Empirical formula is the simplest whole number ratio of atoms present in a covalent compound. For example, the covalent compound silica (sand) has simplest ratio of 1:2 of silicon and oxygen atoms respectively. Therefore, its empirical formula is SiO2. Formula unit is defined as the simplest whole number ratio of ions, as present in the ionic compound. In other words, ionic compounds have only empirical formulae. Their molecular formula and formula unit is same. For example, formula unit of common salt consists of one Na+ and one CI– ion and its empirical formula is NaCl.

2. How can you differentiate between molecular formula and empirical formula? Ans. Empirical formula is the simplest whole number ratio of atoms present in a compound. The empirical formula of a compound is determined by knowing the percentage composition of a compound. Molecular formula shows the actual number of atoms of each element present in a molecule of that compound. Molecular formula is derived from empirical formula by the following relationship:

Molecular formula = (Empirical formula) x n

Where n is 1,2,3 and so on.

3. Identify the following formulae as empirical or molecular formula: H2O2 , CH4 , C6H12O6 , C12H22O11 , BaCO3 , KBr? Ans.

Empirical formula Molecular formula BaCO3, KBr H2O2 , CH4 , C6H12O6 , C12H22O11

4. What is empirical formula of acetic acid (CH3COOH)?

Ans. Empirical formula of acetic acid is CH2O.

5. Calculate the formula masses of: Na2SO4 , ZnSO4 and CuCO3?

Ans. To calculate formula mass of Na2SO4 :

Atomic mass of sodium = 23 amu

Atomic mass of sulphur = 32 amu

Atomic mass of oxygen = 16 amu

Formula mass of Na2SO4 = 2(atomic mass of sodium atom) + (atomic mass of

sulphur) + 4(atomic mass of oxygen)

= (2x23) + 32 + (4x16)

= 46 + 32 +64 = 142 amu

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To calculate formula mass of ZnSO4:

Atomic mass of zinc = 65.38 amu

Atomic mass of sulphur = 32 amu


Formula mass of ZnSO4 = (atomic mass of zinc) + (atomic mass of

Sulphur) + 4(atomic mass of oxygen)

= 65.38 +32 + 4x16 = 65.38 +32 + 64

= 161.38 amu

To calculate formula mass of CuCO3:

Atomic mass of copper = 63.5 amu

Atomic mass of carbon = 12 amu


Formula mass of CuCO3 = 63.5 + 12 + 3x16 = 123.5 amu

Test yourself 1.5

• Identify the followings as diatomic, triatomic or polyatomic molecules H2.SO4, H2, CO2, HCI, CO, C6H6, H2O

Ans. Diatomic molecule H2, HCI, CO Triatomic molecule CO2, H2O Polyatomic molecule H2.SO4 , C6H6

• Identify among the followings as cation, anion, free radical, molecular ion or molecule:

Na+, Br ., N2+ , N2, CI2, CO32--, H-, O2, O

2-

Ans.

Cation Na+, N2+

Anion CO32-, H-, O2-

Free radical Br .

Molecular ion N2+ , CO3

2-, O2-

Molecule N2, CI2, , O2,

Test yourself 1.6

1. Which term is used to represent the mass of 1 mole of molecules of a substance? Ans. The term gram molecular mass is used to represent the mass of 1 mole of molecules of a substance.

2. How many atoms are present in one gram atomic mass of a substance? Ans. Avogadro’s number (6.02 x 1023) of atoms are present in one gram atomic mass of a substance.

3. Explain the relationship between mass and mole of a substance? Ans. we can calculate the number of moles of a substance from the known mass of the substance with the help of following equation:

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4. Find out the mass of 3 moles of oxygen atoms? Ans. Mass of 3 moles of oxygen atoms = no. of moles x molar mass of oxygen = 3 x 16 = 48 g/mol

5. How many molecules of water are present in half mole of water?

Ans. Solution:

Number of molecules present in 1 mole of water = 6.02 x 1023

Number of molecules present in half (1/2) mole of water = 6.02 x 1023/2

= 3.01 x 1023

1. How many atoms of sodium are present in 3 moles of sodium and what is the mass of

it? Ans. 1 mole of sodium contains atoms = 6.02 x 1023 Number of atoms of sodium in 3 moles = 3x 6.02 x 1023

= 18.06 x 1023

2. How many atoms are in 1 amu and 1 g of hydrogen (H)? Ans.

Number of atoms in1 gram of hydrogen = 6.02 x 1023

The atomic mass of hydrogen = 1.008 g Number of atoms in1 amu of hydrogen = 6.02 x 1023

1.008 = 5.97 x 1023

3. How many atoms are present in 16 g of O and 8g of S? Ans.

Atomic mass of oxygen = 16 g Number of atoms in 16 g of O = 6.02 x 1023

Atomic mass of sulphur = 32 g \ 32 g of S contains atoms = 6.02 x 1023

1 g of S contains atoms = 6.02 x 1023 32 8 g of S contains atoms = 8x 6.02 x 1023 32

= 1.505x1023

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4. Is the mass of 1 mole of O and 1 mole of S same?

Ans. No, mass of 1 mole of sulphur is two times the mass of 1 mole of oxygen.

5. What do you mean by 1 atom of C and 1 gram atom of C? Ans. 1 atom of C means one single atom of carbon while 1 gram atom of C means 12 g of carbon which contains 6.02 x 1023 number of carbon atoms.

6. If 16 g of oxygen contains 1 mole of oxygen atoms calculate the mass of one atom of oxygen in grams? Ans. Solution: 1 Mole (6.02 x 1023 atoms) of oxygen has mass = 16 g 1 atom has mass = 16_______ 6.02 x 1023 = 2.66 x 10--23 g

7. How many times is 1 mole of oxygen atom heavier than 1 mole of hydrogen atom? Ans. Solution Mass of 1 mole of hydrogen = 1.008 g Mass of 1 mole of oxygen = 16 g So, we can say that mass of 1 mole of oxygen is 16 times heavier than mass of 1 mole of hydrogen.

8. Why does 10 g nitrogen gas contain the same number of molecules as 10 g of carbon

monoxide?

Ans. Molar mass of nitrogen gas and carbon monoxide is same i.e. 28g. That’s why 10 g

nitrogen gas contain the same number of molecules as 10 g of carbon monoxide.

SHORT ANSWER QUESTIONS

1. Define industrial chemistry and analytical chemistry? Ans. The branch of chemistry that deals with the manufacturing of chemical compounds on commercial scale is called industrial chemistry. Analytical chemistry is the branch of chemistry that deals with separation and analysis of a sample to identify its components.

2. How can you differentiate between organic and inorganic chemistry? Ans. Organic Chemistry is the study of covalent compounds of carbon and hydrogen 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.

3. Give the scope of biochemistry? Ans. The applications of biochemistry are in the fields of medicine, food science and agriculture, etc.

4. How does homogeneous mixture differ from heterogeneous mixture? Ans. Mixtures that have uniform composition throughout are called homogeneous mixtures e.g. air, gasoline, ice cream. Heterogeneous mixtures are those in which composition is not uniform throughout e.g. soil, rock and wood.

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 the atoms of that element as compared to 1/12th (one-twelfth) the mass of an atom of carbon- 12 isotope. When this atomic mass unit is expressed in grams, it is:

1 amu = 1.66 x 10-24g

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6. Define empirical formula with an example?

Ans. The simplest type of formula is empirical formula. It is the simplest whole number ratio of atoms present in a compound. Glucose has simplest ratio 1:2:1 of carbon, hydrogen and oxygen atoms, 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 formed by the simple mixing of different gases while water is formed by the chemical combination of hydrogen and oxygen atoms.

Air does not have any chemical formula while water has a chemical formula H2O.

Components of air can be separated by simple physical methods while water can not be separated into its components by physical methods.

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

compound? Ans.

Hydrogen and oxygen are elements because they can not be broken down into simpler substances while water is a compound because it can be broken down into its components.

Both Hydrogen (H2) and oxygen (O2) molecules exits as homoatomic molecules which is a characteristic of an element while water is a heteroatomic molecule which is a characteristic of a compound.

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

Ans.

Symbol is a short hand name of an element.

Symbol of an element helps to write chemical formula of a compound.

In a balanced chemical equation symbol of an element tells number of moles of that element taking part in a chemical reaction.

Symbol of an element (in cation or anion form) shows its combining capacity with other atoms.

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

Ans.

Soft drink is formed by simple mixing of its components (water, sugar and carbon dioxide) while water is formed by the chemical combination of hydrogen and oxygen.

Components of soft drink do not have any fixed ratio while hydrogen and oxygen have fixed ratio 1:8 by mass in water.

Components of soft drink can be separated by simple physical means while components of water (H2 and O2) can not be separated by simple physical means.

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.

i. He and H2 both are elements ii. CO is a compound and Co is an element iii. Water is a compound and milk is a mixture iv. Gold is an element and brass is a mixture v. Iron is an element and steel is a mixture

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12.Define atomic mass unit. Why is it needed? Ans. One atomic mass unit (amu) is 1/12th the mass of one atom of carbon-12. When this atomic mass unit is expressed in grams, it is:

1 amu = 1.66 x 10--24g As we know that the mass of an atom is too small to be determined practically. However, certain instruments enable us to determine the ratio of the atomic masses of various elements to that of carbon-12 atoms. This ratio is known as the relative atomic mass of the element. This is the main reason to have a relative atomic mass unit.

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.

i. Zinc + Copper is a mixture named as brass ii. Water + Sugar is mixture named as sugar solution iii. Aluminium + Sulphur is a compound named as aliminium suphide (Al2S3) iv. Iron + Chromium + Nickel is an alloy named as nikrome

14. Differentiate between molecular mass and formula mass, which of the followings have molecular formula? H2O, NaCl, KI, H2SO4

Ans. The sum of atomic masses of all the atoms present in one molecule of a molecular substance, is its molecular mass. For example, molecular mass of water (H2O) is 18 amu. Formula mass is the sum of atomic masses of all the atoms present in one formula unit of an ionic substance. For example, formula mass of sodium chloride (NaCl) is 58.5 amu.

H2O and H2SO4 are molecular formulas.

NaCl and KI are formula units. 15. Which one has more atoms: 10 g of Al or 10 g of Fe? Ans. Calculations show that 10 g of Al has more atoms than 10 g of Fe. 16. Which one has more molecules: 9 g of water or 9 g of sugar (C12H22O11)? Ans. Calculations show that 9 g of water has more molecules than 9 g of sugar. 17. Which one has more formula units: 1 g of NaCl or 1 g of KCl? Ans. Calculations show that 1 g of NaCl has more formula units than 1 g of KCl. 18. Differentiate between homoatomic and heteroatomic molecules with examples. Ans. A Molecule containing same type of atoms is called homoatomic molecule. For example: hydrogen (H2), ozone (O3), sulphur (S8) and phosphorus (P4) are the examples of molecules formed by the same type of atoms. When a molecule consists of different kinds of atoms, it is called heteroatomic molecule. For example: CO2, H2O and NH3 19. In which one of the followings the number of hydrogen atoms is more? 2 moles of HC1 or 1 mole of NH3 ? Ans. Calculations show that 1 mole of NH3 has more hydrogen atoms than 2 moles of HCl

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