Chapter 1 FUNDAMENTALS OF CHEMISTRY – 9th Class Chemistry Notes

Question#1) Write a short note on history of chemistry?

Answer:History of Chemistry: Chemistry derived its name from word alchemy, which is a European word derived from the Arabic word al-kimia. Alkemai is the old name of Egypt. The word alcheme, khame, kheme means black earth. It refers to the black soil crust of Egypt. When the word chemistry shifted to europeit became alchemistry and finally chemistry. According to some chemists kimia is a Persian word which means gold. This word is revolutionized by muslim scientists. Muslim scientists were interested in the conversion of bases metals lead, copper into gold, that’s why chemistry is also called the art of metal working. Thus the muslim scientists laid down the foundation of the modern chemistry. Jabir ibn Hayyan was the first muslim scientist who defined alchemia or chemistry and that’s why he is called the father of chemistry.

 

Q2) Define science and chemistry? What are the major branches of chemistry?

Answer: Science: word science is derived from “scientia” means “knowledge”. The knowledge that provides understanding of this world and how it works is called science. The knowledge obtained through observations and experiments is called science.

Chemistry: The branch of science that deal with the composition, structure, properties and reactions of matter is called chemistry.

Major Branches of Chemistry: The major branches of chemistry are as follows:

1) Physical chemistry:  Physical Chemistry is defined as the branch of chemistry that deals with the relationship between the composition and physical properties of matter along with the changes in them.

Scope: The properties such as structure of atoms or formation of molecules behavior of gases, liquids and solids and the study of the effect of temperature or radiation on matter are studied under this branch.

2) Organic Chemistry:

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

Occurrence and scope: Organic compounds occur naturally and are also synthesized in the laboratories. Organic chemists determine the structure and properties of these naturally occurring as well as synthesized compounds. Scope of this branch covers petroleum, petrochemicals and pharmaceutical industries.

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.

Scope: It has applications in every aspect of the chemical industry such as glass, cement, ceramics and metallurgy (extraction of metals from ores).

Biochemistry It is the branch of chemistry in which we study the structure, composition, and chemical reactions of substances found in living organisms.

Scope: It covers all chemical processes taking place in living organisms, such as synthesis and metabolism of biomolecules like carbohydrates, proteins and fats. Biochemistry emerged as a separate discipline when scientists began to study how living things obtain energy from food or how the fundamental biological changes occur during a disease. Examples of applications of biochemistry are in the fields of medicine, food science and agriculture, etc.

Industrial Chemistry:

The branch of chemistry that deals with the manufacturing of chemical compounds on commercial scale, is called industrial chemistry.

Scope: It deals with the manufacturing of basic chemicals such as oxygen, chlorine, ammonia, caustic soda, nitric acid and sulphuric acid. These chemicals provide the raw materials for many other industries such asNuclear Chemistry

Nuclear Chemistry is the branch of chemistry that deals with the radioactivity, nuclear processes and properties.

Scope:The main concern of this branch is with the atomic energy and its uses in daily life. It also includes the study of the chemical effects resulting from the absorption of radiation within animals, plants and other materials. It has vast applications in medical treatment (radiotherapy), preservation of food and generation of electrical power through nuclear reactors, etc.

Environmental Chemistry:

It is the branch of chemistry in which we study about components of the environment and the effects of human activities on the environment. Environmental chemistry is related to other branches like biology, geology, ecology, soil and water. The knowledge of chemical processes taking place in environment is necessary for its improvement and protection against pollution.

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. Qualitative analysis provides the identity of a substance (composition of chemical species). On the other hand, quantitative analysis determines the amount of each component present in the sample. Hence, in this branch different techniques and instruments used for analysis are studied.

Scope: The scope of this branch covers food, water, environmental and clinical analysis.

Q#3)Write short notes on following terms.

1) Matter and its types 2) Physical properties and Chemical properties.3)Elements and its types. 4)Mixture and its types 5) compound and its types.

Answer: 1) Matter:Anything that has mass and occupies space is called matter. Our bodies as well as all the things around us are examples of matter.

Types of matter: there are two types of matter.

  1. A) Substance:A piece of matter in pure form is termed as a substance. Every substance has a fixed composition and specific properties or characteristics. Examples: compounds, molecule, atom, element.
  2. B) Mixture:Impure matter is called a mixture; which can be homogeneous or heterogeneous in its composition.

Example: sugar dissolved in water.

2) Physical properties: The properties those are associated with the physical state of the substance are called physical properties like colour, smell, taste, hardness, shape of crystal, solubility, melting or boiling points, etc. For example, when ice is heated, it melts to form water. When water is further heated, it boils to give steam. In this entire process only the physical states of water change whereas its chemical composition remains the same.

 

Chemical properties: The chemical properties depend upon the composition of the substance. When a substance undergoes a chemical change, its composition changes and a new substances are formed. For example, decomposition of water is a chemical change as it produces hydrogen and oxygen gases. All materials are either a substance or a mixture.

 

3)Elements:substances made up of same type of atoms, having same atomic number and cannot be decomposed into simple substances by ordinary chemical means are called elements.  Or substance in which all the atoms are identical and  valenticle is called element.

Total elements in the world: 118 elements have been discovered, out of which 92 are naturally occurring elements and 18 elements are artificially synthesized in the labortary and are called synthetic elements..

Explanation: Each element is made up of unique type of atoms that have very specific properties.

 

Elements occur in nature in free or combined form. All the naturally occurring elements found in the world have different percentages in the earth’s crust, oceans and atmosphere. Natural occurrence by weight percent of some naturally occurring elements.

 

Earth’s Crust Oceans Atmosphere
 

Oxygen 47%

 

Silicon 28%

 

Aluminium 7.8%

 

Oxygen 86%

 

Hydrogen 11%

 

Chlorine 1.8%

 

Nitrogen 78%

 

Oxygen 21%

 

Argon 0.9%

 

Classification of elements:

Elements may be solids, liquids or gases. Majority of the elements exist as solids e.g. sodium, copper, zinc, gold, etc. There are very few elements which occur in liquid state e.g. mercury and bromine. A few elements exist as gases e.g. nitrogen, oxygen, chlorine and hydrogen.

 

On the basis of their properties, elements are divided into metals (sodium) , non-metals (Chlorine) and metalloids (Boron). About 80 percent of the elements are metals.

Chemical composition of living body: Major part of a living body is made up of water i.e. 65% to 80% by mass.

Six elements constitute about 99% of our body mass; namely: Oxygen 65 %, Carbon 18%, Hydrogen 10 %, Nitrogen 3%, Calcium 1.5% and Phosphorus 1.5%. Potassium, Sulphur, Magnesium and Sodium constitute 0.8% of our body mass. Whereas Copper, Zinc, Fluorine, Chlorine, Iron, Cobalt and Manganese constitute only 0.2% of our body mass.

Symbol of the elements: The abbreviated name of an element is called symbol. Elememns are represented by these symbols.

Roles for assigning symbols to an element: A symbol is taken from the name of that element in English, Latin, Greek or German. If it is one letter, it will be capital as H for Hydrogen, N for Nitrogen and C for Carbon etc. In case of two letters symbol, only first letter is capital e.g. Ca for Calcium, Na for Sodium and Cl for Chlorine.

 

Valency:Thecombining capacity of an element with other elements is called valency. It is the unique property of an element. It depends upon the number of electrons in the outermost shell.

In simple covalent compounds, valency is the number of hydrogen atoms which combine with one atom of that element or the number of bonds formed by one atom of that element e.g. in the following compounds.

 

HCl, H2O, NH3  and  CH4.

 

The valency of chlorine, oxygen, nitrogen and carbon is 1, 2, 3 and 4, respectively.

 

In simple ionic compounds valency is the number of electrons gained or lost by an atom of an element to complete its octet. Elements having less than four electrons in their valence shell; prefer to lose the electrons to complete their octet. For example, atoms of Na, Mg and Al have 1, 2 and 3 electrons in their valence shells respectively. They lose these electrons to have valency of 1, 2 and 3, respectively. On the other hand, elements having five or more than five electrons in their valence shells, gain electrons to complete their octet. For example, N, O and Cl have 5, 6 and 7 electrons in their valence shells respectively. They gain 3, 2 and 1 electrons respectively to complete their octet. Hence, they show valency of 3, 2 and 1, respectively. A radical is a group of atoms that have some charge. Valencies of some common elements and radicals are shown in Table.

Element/Radical Symbol Valency Element/Radical Symbol Valency
Sodium Na 1 Hydrogen H 1
Potassium K 1 Chlorine Cl 1
Silver Ag 1 Bromine Br 1
Magnesium Mg 2 Iodine I 1
Calcium Ca 2 Oxygen O 2
Barium Ba 2 Sulphur S 2
Zinc Zn 2 Nitrogen N 3
Copper Cu 1,2 Phosphorus P 3,5
Mercury Hg 1,2 Boron B 3
Iron Fe 2,3 Arsenic As 3
Aluminium Al 3 Carbon C 4
Chromium Cr 3 Carbonate CO32– 2
Ammonium NH4+ 1 Sulphate SO42– 2
Hydronium H3O+ 1 Sulphite SO32– 2
Hydroxide OH 1 Thiosulphate S2O32– 2
Cyanide CN 1 Nitride N3 3
Bisulphate HSO4 1 Phospate PO43– 3
Bicarbonate HCO3 1

 

Some elements show more than one valency, i.e. they have variable valency. For example, in ferrous sulphate (FeSO4 ) the valency of iron is 2. In ferric sulphate (Fe2(SO4)3), the valency of iron is 3. Generally, the Latin or Greek name for the element (e.g., Ferrum) is modified to end in ‘ous’ for the lower valency (e.g. Ferrous) and to end in ‘ic’ for the higher valency (e.g. Ferric).

 

4)Mixture: when two or more substances (elements or compounds) mix up physically without any fixed ratio by mass, they form a mixture. Mixture is of two types.

 

HOMOGENOUS MIXTURE: Mixtures that have uniform composition throughout are called homogeneous mixtures e.g. air, gasoline, ice cream.

HETEROGENOUS MIXTURE: heterogeneous mixtures are those in which composition is not uniform throughout e.g. soil, rock and wood.without any fixed ratio, they form a mixture. On mixing up, the component substances retain their own chemical identities and properties.

 

The mixture can be separated into parent components by physical methods such as distillation, filtration, evaporation, crystallization or  magnetization.

Examples: a) Air is a mixture of nitrogen, oxygen, carbon dioxide, noble gases and water vapours. b) Soil is a mixture of sand, clay, mineral salts, water and air.

c) Milk is a mixture of water, sugar, fat, proteins, mineral salts and vitamins.

d) Brass is a mixture of copper and zinc metals.

 

5) Compound:Compound is a substance made up of two or more elements chemically combined together in a fixed ratio by mass. As a result of this combination, elements lose their own properties and produce new substances (compounds) that have entirely different properties. Compounds can’t be broken down into its constituent elements by simple physical methods. For example, carbon dioxide is formed when elements of carbon and oxygen combine chemically in a fixed ratio of 12:32 or 3:8 by mass. Similarly, water is a compound formed by a chemical combination between hydrogen and oxygen in a fixed ratio of 1:8 by mass.

Classification of compounds: compounds are of following types.

1) Ionic compounds: Examples: NaCl, KBr, CuSO4.

  • Covalent compounds: Examples: H2O, HCl, etc.
  • Coordinate covalent compounds: Examples: NH4+, H3O+ .

 

Some common compounds with their formulae.

Compound Chemical Formula
Water H2O
Sodium Chloride (Common Salt) NaCl
Silicon Dioxide (Sand) SiO2
Sodium Hydroxide (Caustic Soda) NaOH
Sodium Carbonate (Washing Soda) Na2CO3.10H2O
Calcium Oxide (Quick Lime) CaO
Calcium Carbonate (Limestone) CaCO3
Sugar C12H22O11
Sulphuric Acid H2SO4
Ammonia NH3

 

Q#4) What is the difference between compound and mixture?

 

Answer:Difference between a Compound and a Mixture

 

S.No    Compound     Mixture
1 It is formed by a chemical combination of atoms of the elements. Mixture is formed by the simple mixing up of the substances.
2 The constituents lose their identity and form a new substance having entirely different properties from them. Mixture shows the properties of the constituents.
3 Compounds always have fixed composition by mass. Mixtures do not have fixed composition.
4 The components cannot be separated by physical means. The components can be separated by simple physical methods.
5 Every compound is represented by a chemical formula. It consists of two or more components and does not have any chemical formula.
6 Compounds have homogeneous composition. They may be homogeneous or heterogeneous in composition
7 Compounds have sharp and fixed melting points Mixtures do not have sharp and fixed melting points.

 

 

Q#5) Write a short note atom?

 

Answer: Atom: (Derived from word atomos means indivisible but still atoms are divisible) smallest particle of an element which can take part in a chemical reaction is known as atom. Or The smallest building block of an element is called atom. Atoms of the same element are alike. For example gold element contain all gold atoms. Each atom of gold is approximately 10-10 meter in diameter.

 

Q#6) Write a detailed note on atomic number and mass number?

Answer: Atomic number or proton number or identification number:

The number of protons present in the nucleus of an atom is called proton number or atomic number.

Explanation:It is represented by symbol ‘Z’ . As all atoms of an element have the same number of protons in their nuclei, they have the same atomic number.Hence, each element has a specific atomic number termed as its identification number. For example, all hydrogen atoms have 1 proton, their atomic number is Z=l. All atoms in carbon have 6 protons, their atomic number is Z=6. Similarly, in oxygen all atoms have 8 protons having atomic number Z=8 and sulphur having 16 protons shows atomic number Z = 16.

Mass number:The mass number is the sum of number of protons and neutrons present in the nucleus of an atom. It is represented by symbol ‘A’.

 

Caculation: It is calculated as A=Z+n where n is the number of neutrons and Z is number of protons.

Each proton and neutron has lamu mass. For example, hydrogen atom has one proton and no neutron in its nucleus, its mass number A=l+0 =1. Carbon atom has 6 protons and 6 neutrons, hence its mass number A=12. Atomic numbers and mass numbers of a few elements are given in Table.

Element Number of Protons Number of Neutrons

(n= A-Z)

Atomic Number (Z) Mass Number (A)
Hydrogen 1 0 1 1
Carbon 6 6 6 12
Nitrogen 7 7 7 14
Oxygen 8 8 8 16
Fluorine 9 10 9 19
Sodium 11 12 11 23
Magnesium 12 12 12 24
Potassium 19 20 19 39
Calcium 20 20 20 40

 

Q#7)Define relative atomic mass and atomic mass unit? Why atomic mass unit is needed?

Answer: Relative Atomic Mass: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 (an element having different mass number but same atomic number).

EXPLANATION: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.  Based on carbon-12 standard, the mass of an atom of carbon is 12 units and l/12th of it comes to be1 unit. When we compare atomic masses of other elements with atomic mass of carbon- 12 atom, they are expressed as relative atomic masses of those elements.

Atomic mass unit:One atomic mass unit is 1/12th the mass of one atom of carbon-12th.The unit for relative atomic masses is called atomic mass unit, with symbol ‘amu’.  When this atomic mass unit is expressed in grams, it is:

1 amu = 1.66 x 10-24g.

For example:

Mass of a Proton = 1.0073 amu or 1.672 x 10-24g

Mass of a Neutron = 1.0087 amu or 1.674 x 10-24g

Mass of an Electron = 5.486 x 10–4 amu or 9.106 x 10-28g.

Use and need of atomic mass unit: The mass of an atom is too small to be determined practically, so they are compared with C-12 isotope. This enable us to determine the mass of an atom.

Q#8) Define chemical formula? What are the types of chemical formula? Also write the importance of chemical formula?

Chemical formula: The symbolic representation of all the elements(atoms) in the compound is called chemical formula. OR The way of representing of a molecule or a compound using the symbols of its elements.

How to write a Chemical Formula:

Compounds are represented by chemical formulae as elements are represented by symbols. Chemical formulae of compounds are written keeping the following steps in consideration.

 

  1. Symbols of two elements are written side by side, in the order of positive ion first and negative ion later.
  2. The valency of each ion is written on the right top corner of its symbol, e.g. Na+, Ca2+, CI– and O2–.

3. This valency of each ion is brought to the lower right corner of other ion by ‘cross-exchange’ method, e.g.

4. If the valencies are same, they are offset (ignored) and are not written in the chemical formula. But if they are different, they are indicated as such at the same position, e.g. in case of sodium chloride both the valencies are offset and formula is written as NaCl, whereas, calcium chloride is represented by formula CaCl2.

 

5. If an ion is a combination of two or more atoms which is called radical, bearing a net charge on it, e.g. SO42–(sulphate) and PO43–(phosphate), then the net charge represents the valency of the radical. The chemical formula of such compounds is written as explained in (3) and (4); writing the negative radical within the parenthesis. For example, chemical formula of aluminium sulphate is written as Al2(SO4)3 and that of calcium phosphate as Ca3(PO4)2

 

Significance of chemical formula:

Types of chemical formulas: There are two types of chmical formulas.

1) Emperical formula.  2) Molecular formula.

Empirical formula: The formula that shows simplest whole number ratio of elements present in a compound is called empirical formula.

It is the simplist type of formula.

Determination of emperical formula; The empirical formula of a compound is determined by knowing the percentage composition of a compound.

 

The covalent compound silica (sand) has simplest ratio of 1:2 of silicon and oxygen respectively. Therefore, its empirical formula is SiO2 Similarly, glucose has 2 simplest ratio 1:2:1 of carbon, hydrogen and oxygen, respectively. Hence, its empirical formula is CH2O.

 

Formula unit: The simplest whole number ratio of ions, as present in the ionic compound is called formula unit.   OR   The simplest unit taken as a representative of an ionic compound is called formula unit. Ionic compounds have only empirical formulae. For example, formula unit of common salt consists of one Na+ and one CI ion and its empirical formula is NaCl. Similarly, formula unit of potassium bromide is KBr, which is also its empirical formula.

 

 

Molecular Formula: formulae that show actual number of atoms of each element present in a molecule of that compound  is called molecular formula.

Molecules are formed by the combination of atoms. These molecules are represented by molecular formula.

Derivation of molecular formula:molecular formula is derived from empirical formula by the following relationship:

Molecular formula = (Empirical formula)n

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

For example, molecular formula of benzene is C6H6 which is derived from the

empirical formula CH where the value of n is 6.

 

The molecular formula of a compound may be same or a multiple of the empirical formula. A few compounds having different empirical and molecular formulae are shown in Table.

 

Some Compounds with their Empirical and Molecular Formulae.

Compound Emperical Formula Molecular Formula
Hydrogen peroxide HO H2O2
Benzene CH C6H6
Glucose CH2O C6H12O6

 

Some compounds may have same empirical and molecular formula e.g. water (H2O) hydrochloric acid (HCl), etc.

 

Q#9) What do you know about molecular and formula mass?

Answer: Molecular Mass:

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 chlorine (Cl2 ) is 71.0 amu, of water (H2O) is 18 amu and that 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. Some ionic compounds that form three dimensional solid crystals, are represented by their formula units. Formula mass in such cases is the sum of atomic masses of all the ions present in a formula unit.  For example, formula mass of sodium chloride is 58.5 amu and that of CaCO3 is 100 amu.

 

 

Q#10) Define chemical species? Explain in detail the types of ions?

Answer: Chemical species: Atom or group of atoms which can take part in a chemical reaction or that is produced after a chemical reaction as a highly reactive substance is called chemical species.

Types of chemical species: Following are the main types of chemical species.

1) ions  2) Free Radicals.

1) Ion is an atom or group of atoms having a charge on it. The charge may be positive or negative. On the basis of charge assigned to an ion, there are two types of ions.

A) Cations B) Anions.

A) Cations :An atom or group of atoms having positive charge on it is called cation.  For example, Na+, K+are cations. The cations are of two types.

I)Atomic cation:An atom having positive charge on it is called atomic cation. Examples: Na+, Ca+, H+, etc.

II)Molecular cation(cationic molecular ion)Agroup of atoms or molecule having positive charge on it is called molecular cation. Examples: NH4+, H3O+, etc.

Formation of cations: cation are formed when atom(s) lose electrons from their outermost shells. The following equations show the formation of cations from atoms.

  1. B) Anion: An atom or a group of atoms that has a negative charge on it, is called anion.

Types of anions: anions are of two types.

  1. I) Atomic anion:An atom that has a negative charge on it, is called atomic anion. EXAMPLES: O-2, Cl, F, etc.

II)Molecular anion (anionic molecular ion): A group of atoms that has a negative charge on it, is called anion.

Examples: SO4-2, H2PO4, etc.

Formation: Anion is formed by the gain or addition of electrons to an atom. For example, Cl and O2-. Following examples show the formation of an anion by addition of electrons to an atom.

  • Molecular ion:Group of atoms or molecule having a charge on it is called molecular ion. Molecular ions are of two types.

 

I)Molecular cation(cationic molecular ion) :Agroup of atoms or molecule having positive charge on it is called molecular cation. Examples: NH4+, H3O+

 

II)Molecular anion(anionic molecular ion) Agroup of atoms or molecule having negative charge on it is called molecular anion. Examples: SO4-2, H2PO4-, etc.

Free Radicals:

Free radicals are atoms or group of atoms possessing odd number of (unpaired) electrons. It is represented by putting a dot over the symbol of an element e.g. H., CI., H3C.. Free radicals are generated by the homolytic (equal) breakage of the bond between 3 two atoms when they absorb heat or light energy. A free radical is extremely reactive species as it has the tendency to complete its octet.

Q#11) Write a note on cleavage and its types?

Answer: Cleavage: The splitting or breakage of the bond between two atoms due to absorption of heat or light energy is called cleavage.

Types of cleavage: there are two types of cleavage.

  • Homolytic cleavage: Equal breakage of bond between two atoms is called homolytic cleavage. As a result of homolytic cleavage free radicals are formed.

Example: H2 + energy → 2H

Heterolytic cleavage: unequal breakage of bond between two atoms is called heterolytic cleavage. Example: HCl+energy → H+ + Cl

 

Q#12) Differentiate between atom and ion?

Answer:

Differences between atom and ion.

Atom Ion
1. It is the smallest particle of an element. It is the smallest unit of an ionic compound.
2. it can or cannot exist independently and can take part in a chemical reaction. It cannot exist independently and is surrounded by oppositely charged ions.
3. it is electrically nuetral It has a net charge (either negative or positive)

 

Q#13) what are the basic differences among molecule and molecular ion?

 

Answer: Differences between molecule and molecular ion.

Molecule Molecular Ion
1. It is the smallest particle of an element or compound which can exist independently and shows all the properties of that compound. It is the formed by gain or loss of electrons by a molecule.
2. it is always neutral. It have negative or positive charge.
3. it is formed by the combination of atoms. it is formed by the ionization of molecules.
4. It is a stable unit. It is a reactive specie.

 

 

Q#14) Differentiate between ion and free radical?

 

Answer: Differences between ion and free radical.

 

Ions Free Radicals
1. These are the atoms which bear some charge. These are the atoms that have odd number of electrons.
2. They exist in solution or in crystal lattice. They can exist in solutions as well in air.
3. Their formation is not affected by the presence of light. They may form in the presence of light.

 

 

Q#15) Define molecule? Classify molecules on the basis of number and nature of atoms?

Answer: Molecule: The smallest component of a substance (an element or a compound) that can exist independently or freely in nature is called a molecule. A molecule is  mostly formed by the chemical combination of atoms. It is the smallest unit of a substance. It shows all the properties of the substance and can exist independently.

Types of Molecules:

Molecules are classified on different basis. Some of the important classification are as follows…….

  1. A) Classification of molecules on the basis of number of atoms:on the basis of number of atoms, molecules are of following types.

1)Monoatomic molecule:A molecule consisting of only one atom is called monoatomic molecule. For example, the inert gases helium, neon and argon all exist independently in atomic form and they are called monoatomic molecules.

2)Diatomic molecule: A molecule consists of two atomsis called diatomic molecule. For example: hydrogen (H2), oxygen (O2), chlorine (Cl2) and hydrogen chloride (HCl).

3)Triatomic molecule: A molecule consisting of three atomsis called triatomic molecule. For example: H2O and CO2.

4) Polyatomic molecule: A molecule consisting of many atoms is called polyatomic molecule.For example: methane (CH4), sulphuric acid (H2SO4) and glucose (C6H12O6).

  1. B) Classification of molecules on the basis of nature(type) of atoms.

1) Homoatomic molecule: A Molecule containing same type of atoms, is called homoatomic molecule.For example: hydrogen (H2), ozone (O3), sulphur (S8) and phosphorus (P4).

Heteroatomic molecule:When a molecule consists of different kinds of atoms, it is called heteroatomic molecule. For example: CO2, H2O and NH3.

Q#16) Define the following terms?

  1. Gram atomic mass
  2. Gram molecular mass

iii. Gram formula mass

 

Answer: 1)Gram Atomic Mass:

The atomic mass of an element expressed in grams is called gram atomic mass or gram atom. It is also called a mole.

1 gram atom of hydrogen = 1.008 g = 1 mol of hydrogen

1 gram atom of carbon = 12.0 g = 1mol of carbon

It means that 1 gram atom of different elements has different masses.

 

2) Gram Molecular Mass

The molecular mass of an element or a compound expressed in grams is called gram molecular mass or gram molecule. It is also called a mole.

1 gram molecule of H2 = 2.0 g = 1 mol of hydrogen

1 gram molecule of H2O = 18.0 g = 1 mol of water

1 gram molecule of H2SO4 =98.0 g = 1 mol of sulphuric acid

 

3) Gram Formula Mass

The formula mass of an ionic compound expressed in grams is called gram formula mass or gram formula. This is also called a mole.. For example:

1 gram formula of NaCI = 58.5 g = 1 mol of sodium chloride

1 gram formula of CaCO3 = 100 g = 1 mol of calcium carbonate

 

Q#17) Define mole and avogadro’s number? Why mole is called chemist secret unit?  OR   Mole is SI unit for the amount of a substance. Define it with examples?

Answer: Mole (Chemist secret unit)

A mole is defined as the amount(mass) of a substance that contains 6.02 x 1023 number of particles (atoms, molecules or formula units). OR mole is the atomic mass, molecular mass or formula mass of a substance expressed in grams is called mole. It establishes a link between mass of a substance and number of particles. It is abbreviated as ‘mol’.

 

Avogadro’s Number: Avogadro’s number is the number of particles ( atoms, ions or molecules) in one mole of a substance. OR 6.022 χ 1023 number of atoms, molecules or formula units is called avogadro’s number.  It is symbolized by NA and has a value of

6.022 χ 1023.

  1. one mole of carbon =12 gram= 6.02 x 1023 atoms of carbon = 1NA.
  2. one mole of water= 18gram= 6.02 x 1023 molecules of H2O= 1NA.

iii.one mole of sodium chloride= 58.5gram= 6.02 x 1023 formula units of NaCl = 1NA.

 

 

Amaedo Avogadro

(1776-1856) was an Italian scholar. He is famous for molecular theory commonly known as Avogadro’s law. In tribute to him, the number of particles (atoms, molecules, ions) in mole of a substance 6.02 x 1023is known as the Avogadro’s constant.

 

EXERCISE

 

Short questions:

 

Question#1) Define industrial and analytical chemistry?

Answer: Industrial Chemistry

The branch of chemistry that deals with the manufacturing of chemical compounds on commercial scale, is called industrial chemistry.

Analytical chemistry: Analytical chemistry is the branch of chemistry that deals with separation and analysis of a sample to identify its components.

Question#2) How can you differentiate between organic and inorganic chemistry?

 

Answer: 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.

 

Question#3) Give the scope of biochemistry?

Answer: Scope of Biochemistry: It covers all chemical processes taking place in living organisms, such as synthesis and metabolism of biomolecules like carbohydrates, proteins and fats. Biochemistry emerged as a separate discipline when scientists began to study how living things obtain energy from food or how the fundamental biological changes occur during a disease. Examples of applications of biochemistry are in the fields of medicine, food science and agriculture, etc.

 

Question#4) How does homogeneous mixture differ from heterogeneous mixture?

 

Answer: HOMOGENOUS MIXTURE: Mixtures that have uniform composition throughout are called homogeneous mixtures e.g. air, gasoline, ice cream.

HETEROGENOUS MIXTURE: heterogeneous mixtures are those in which composition is not uniform throughout e.g. soil, rock and wood.

 

Question#5)What is the relative atomic mass? How is it related to gram?

Answer: Relative Atomic Mass: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 (an element having different mass number but same atomic number).When this atomic mass unit is expressed in grams, it is:

1 amu = 1.66 x 10-24g.

 

Question#6) Define empirical formula with an example.

Answer: Empirical formula: The formula that shows simplest whole number ratio of elements present in a compound is called empirical formula.

Example:Emperical formula of glucose( C6H12O6) is CH2O.

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

Answer: Air is a mixture and water is a compound due to following reasons. 1) Air is formed by simple or physical mixing of different gases while water is formed by chemical combination of hydrogen and oxygen. 2) air does not have any chemical formula while water has chemical formula that ia H2O.

  • Components of air can be separated by ordinary physical means while water can not be separated into its components by ordinary physical methods.
  • There is no fixed ratio of gases in air whille in water hydrogen and oxygen has a fixed ratio by mass.

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

Answer: 1)Hydrogen and oxygen can not be broken down into more simpler substances while water can be broken down into its components i,e hydrogen and oxygen.

  • Hydrogen and oxygen exists as homoatomic molecule which is characteristics of elements while water exist as heteroatomic molecule which is characteristics of compound.

Q#9) What is the significance of the symbol of an element?

Answer: Significance of symbol: it is the abbreviated and shortest name , so make study and writing of elements easy. It is used to write chemical formulae of compounds. Symbol of elements in ionic form shows its combining capacity. In a balanced chemical equations it shows the number of moles.

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

Answer: soft drink is formed by simple mixing of water, CO2 and sugar while water is formed by chemical combination of hydrogen and oxygen. Components of soft drink can be easily separated by physical means while components of water can not be separated by physical means. Components of soft drink has no fixed ratio by mass while components of water has fixed ratio by mass.

Q#11) Classify the following into element, compound or mixture:

  1. He and H2 ii. CO and Co iii. Water and milk
  2. Gold and brass v. Iron and steel

Answer: i) He is an element while H2 is is a molecule.

  1. ii) CO is a compound while Co is an elent.

iii) water is a compound while milk is a mixture.

  1. iv) Gold is an element while brass is a mixture.
  2. V) Iron is an element while steel is a mixture.

Q#12) Define atomic mass unit. Why is it needed?

Answer: Atomic mass unit: One atomic mass unit is 1/12th the mass of one atom of carbon-12.

Use and need of atomic mass unit: The mass of an atom is too small to be determined practically, so they are compared with C-12 isotope. This enable us to determine the mass of an atom.

Q#13) State the nature and name of the substance formed by combining the following:

  1. Zinc + Copper ii. Water + Sugar

iii. Aluminium + Sulphur iv. Iron + Chromium + Nickel

Answer: i) By combining zinc and copper, a mixture called brass is formed.

  1. ii) By mixing sugar in water, sugar solution is formed which is a mixture.

iii) By combining aluminium with sulphur, a compound called aluminium sulphide (Al2S3).

  1. iv) By mixing iron , chromium and nickel, an alloy (homogenous mixture) is formed.

 

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

Answer: Molecular Mass:

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 chlorine (Cl2 ) is 71.0 amu, of water (H2O) is 18 amu and that 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 that of CaCO3 is 100 amu.

H2O and  H2SO4 are molecular formulae KI and NaCl are formula units.

 

Q#15) Which one has more atoms: 10 g of Al or 10 g of Fe?

Answer: 10 gram of aluminium(Al) has more atoms than 10 grams of iron(Fe).

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

Answer: 9 gram of water has more molecules than 9 gram of sugar.

Q#17) Which one has more formula units: 1 g of NaCl or 1 g of KCl?

Answer: 1 gram of NaCl has more formula units than 1 gram of KCl.

Q#18) Differentiate between homoatomic and heteroatomic molecules with examples.

Answer: of atoms.

1) Homoatomic molecule:A Molecule containing same type of atoms, is called homoatomic molecule.For example: hydrogen (H2), ozone (O3), sulphur (S8) and phosphorus (P4).

Heteroatomic molecule:When a molecule consists of different kinds of atoms, it is called heteroatomic molecule. For example: CO2, H2O and NH3.

** Homoatomic molecules are formed by homolytic cleavage while heteroatomic molecules are formed by heterolytic cleavage.

Q#19) In which one of the followings the number of 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).

Answer: 1 mole of NH3 has more hydrogen atoms than 2 moles of HCl.

 

 

Long Answer Questions.

 

  1. Define element and classify the elements with examples.

Answer: Please see answer of question number 3 (part 3).

  1. List five characteristics by which compounds can be distinguished from mixtures.

Answer: Please see answer of question number 4.

 

  1. Differentiate between the following with examples:
  2. Molecule and gram molecule
  3. Atom and gram atom

iii. Molecular mass and molar mass

iv.Chemical formula and gram formula

 

Answer:

  1. Molecule:The smallest component of a substance (an element or a compound) that can exist independently or freely in nature is called a molecule. Examples: He, H2, Cl2, O3, etc.

Gram Molecular Mass OR gram molecule:

The molecular mass of an element or a compound expressed in grams is called gram molecular mass or gram molecule. It is also called a mole.

1 gram molecule of H2 = 2.0 g = 1 mol of hydrogen

1 gram molecule of H2O = 18.0 g = 1 mol of water

1 gram molecule of H2SO4 =98.0 g = 1 mol of sulphuric acid

 

  1. ii) Atom: The smallest particle of an element that can exist either alone or in combination and that can show all the properties of the elements and can enter into a chemical reaction is called atom. Examples: hydrogen atom.

Gram atom or gram atomic mass: The atomic mass of an element expressed in grams is called gram atomic mass or gram atom. E.g, gram atomic mass of oxygen is 16 gram.

(iii) Difference between Molar mass and molecular mass: Molar mass is the mass of a mole of an element or a compound while molecular mass is the mass of one molecule of a compound.

Examples: 1) molar mass of carbon is 12 gram.

2) Molecular mass of H2O is 18.

 

(iv) Difference between chemical formula and gram formula:

 Chemical formula: The symbolic representation of elements in a compound is called chemical formula.

Example : Chemical formula of carbon dioxide is CO2.

Gram formula OR  Gram formula mass: The sum of the masses of all the ions present in a formula unit expressed in grams is called gram formula or gram formula mass.

Example: Gram formula mass of sodium chloride is 58.5 gram.

 

 

  1. Mole is SI unit for the amount of a substance. Define it with examples?

Answer: Please see answer of question number 17.

 

 

SOLVED TEST YOURSELVES

 

TESTURSELF 1.1

 

  1. In which branch of chemistry behaviour of gases and liquids is studied?

Answer: The behaviours of gases and liquids are studied in physical chemistry.

 

  1. Define biochemistry?

Answer:Biochemistry: It is the branch of chemistry in which we study the structure, composition, and chemical reactions of substances found in living organisms.

 

  1. Which branch of chemistry deals with preparation of paints and paper?

Answer: Industrial chemistry deals with the preparation of paints and papers.

  1. In which branch of chemistry the metabolic processes of carbohydrates and proteins are studied?

Answer: The metabolic processes of carbohydrates and proteins are studied in biochemistry.

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

Answer: Nuclear chemistry deals with atomic energy and its uses in daily life.

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

Answer: Organic chemistry deals with the structure and properties of naturally occurring molecules.

 

TEST YOURSELF 1.2

 

  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.

Answer: Elements: Aluminium, silicon and tin.

Compounds: Sugar, Table salt and Lime.

Mixtures: Coca cola, petroleum, blood, gun powder, urine and ice cream.

  1. How can you justify that air is a homogenous mixture. Identify substances present in it.

Answer: Air is a homogenous mixture because it has uniform composition throughout. Air is a mixture of carbon dioxide, oxygen, carbon dioxide, noble gases and water.

iii. Name the elementsrepresented by the following symbols:

Hg, Au, Fe, Ni, Co, W, Sn, Na, Ba, Br, Bi.

Answer: Hg= Mercury  , Au= Gold,  Fe=Iron.  Ni=Nickel,  Co=Cobalt,  W=Tungsten,  Sn=Tin,  Na=Sodium,   Ba=Barium,  Br=Bromine, Bi=Bismith.

  1. Name a solid, a liquid and a gaseous element that exists at the room temperature.

Answer: Solid=Gold,   Liquid=Bromine,   Gas=Hydrogen.

  1. Which elements do the following compounds contain?

Sugar, common salt, lime water and chalk.

Answer:

 

Compound Elements
Sugar Carbon, hydrogen and oxygen.
Common salt Sodium and chlorine.
Lime water Calcium, hydrogen and oxygen.
Chalk Calcium, carbon and oxygen.

 

 

TEST YOURSELF 1.3

 

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

Answer: 1 gram of a substance has amu equal to 1 avogadro’s number that is 6.02×1023.

1amu = 1.66×10-24.

amu in 1 gram of a substance (X) = 1g×1amu/1.66×10-24g.

amu in 1 gram of a substance (X) = 0.602×1024amu.

amu in 1 gram of a substance (X) = 6.02×1023amu.

 

  1. Is atomic mass unit a SI unit of an atomic mass?

Answer: Yes, atomic mass unit is a SI unit of an atomic mass.

 

  1. What is the relationship between atomic number and atomic mass?

Answer: Atomic number is the number of protons in the nucleus of an atom while atomic mass is the sum of protons and neutrons in the nucleus of an atom. The relationship between the both are given by the following equasion.

Number of neutrons(n) = A-Z. Where A Is the atomic mass while Z is the atomic number.

 

  1. Define relative atomic mass.

Answer: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 (an element having different mass number but same atomic number).

 

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

Answer: As we know that 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 an element.

 

 

TEST YOURSELF 1.4

 

 

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

Answer: Emperical formula: The formula that shows the simplist whole number ratio of atoms present in a covalent compound is called emperical formula. For example emperical formula of glucose (C6H12O6) is CH2O.

Formula unit: the formula that shows simplist whole number ratio of ions present in an ionic compound is called formula unit. For example, formula unit of common salt, sodium chloride is NaCl.

Both the formulae shows simple ratio. The difference is that one is used for ionic compounds while other is used for covalent compounds.

 

  1. How can you differentiate between molecular formula and empirical formula?

Answer: Emperical formula: The formula that shows the simplist whole number ratio of atoms present in a covalent compound is called emperical formula. For example emperical formula of glucose (C6H12O6) is CH2O.

Molecular formula: The formula that actual number of atoms present in a compound is called molecular formula. For example. Molecular formula of glucose is C6H12O6.

 

 

  1. Identify the following formulae as formulas unit or molecular formulae or emperical formulae.: H2O2, CH4, C6H12O6 , C12H22O11 , BaCO3 , KBr

Answer: Emperical formulae: BaCO3 , KBr.

Molecular formulae: H2O2, CH4, C6H12O6, C12H22O11.

 

  1. What is empirical formula of acetic acid (CH3COOH)? Find out its molecular mass?

Answer: Emperical formula of acetic acid is CH2O.

Molecular mass of acetic acid CH3COOH  OR   C2H4O2 = (12×2) + (1×2)+ (16×2)

Molecular mass of acetic acid CH3COOH  OR   C2H4O2 = 24+2+32

Molecular mass of acetic acid = 58.

 

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

Answer: 1)Formula mass of Na2SO4 = (23×2) + 32 + (16×4)

= 46+32+64= 142amu.

 

2) Formula mass of ZnSO4 = 65+32+(16×4)

 

= 65+32+64=161amu.

 

 

  • Formula mass of CuCO3= 63.5 + 12+ (16×3)

= 63.5+12+48 = 123.5amu.

 

 

 

TEST YOURSELF 1.5

 

Question#1• Identify the followings as diatomic, triatomic or polyatomic molecules

H2SO4, H2, CO2, HCI, CO, C6H6, H2O

Answer: Diatomic molecules: H2, HCl, CO.

Triatomic molecules: CO2, H2O.

Polyatomic molecules: H2SO4, C6H6.

 

 

Question#2• Identify among the followings as cation, anion, free radical, molecular ion or molecule:

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

Answer: Cations: Na+, N2+.

Anions: CO32-, H, O2-.

Free radicals: Br°.

Molecules: N2, Cl2, O2.

Molecular ions: N2+ , CO32-, O2-.

 

 

TEST YOURSELF 1.6

 

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

Answer: The term gram molecular mass is used to represent the mass of 1 mole of molecules of a substance.

 

  1. How many atoms are present in one gram atomic mass of a substance ?

Answer: Avogadro’s number (6.02×1023) of atoms are present in one gram atomic mass of a substance.

 

  1. Explain the relationship between mass and mole of a substance.

Answer: To calculate the number of moles of a substance from the given mass following equasion is used:

Number of moles (n) = Known mass of substance/ molar mass.

 

  1. Find out the mass of 3 moles of oxygen atoms.

Answer: mass = number moles × molar mass

Mass of 3 moles of oxygen = number of moles of oxygen × molar mass

= 3 mol× 16g/mol = 48g.

 

 

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

Answer: number of molecules in one mole of water= 6.02×1023

Number of molecules in half mole of water= 6.02×1023/2

= 3.01×1023 molecules.

 

TEST YOURSELF 1.7

 

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

Answer:  Number of atoms of sodium in one mole = 6.02×1023.

Number of atoms of sodium in one moles= 3× 6.02×1023.

=18.06 × 1023.

Mass of one mole of sodium (atomic mass) = 23.

Mass of 3 moles of sodium= 3mol ×23gram/mol = 69gram

 

 

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

Answer: Number of atoms in 1 gram of hydrogen= 6.02×1023

Atomic mass of hydrogen = 1.008 gram.

Number of atoms in 1 amu of hydrogen = 6.02×1023/1.008

= 5.97×1023

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

Answer: Atomic mass of oxygen= 16 gram= 1 mole

= 1 avogadros number = 6.02×1023 atoms.

Atomic mass of sulphur = 32 gram = 1 mole

= 1 avogadro’s number = 6.02×1023 atoms.

8 gram of sulphur contains = 8×6.02×1023 atoms/32.

= 1.505×1023 atoms.

 

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

Answer: No, mass of 1 mole of oxygen and sulphur is not same. mass of 1 mole of oxygen is 16 gram while that of sulphur is 32 gram. So mass of sulphur is two times the mass of oxygen.

 

  1. What do you mean by 1 atom of C and 1 gram atom of C?

Answer: 1 atom of carbon means 1 single atom of carbon while 1 gram atom of carbon means 1 mole of carbon that is 12 gram and which contains 6.02×1023 atoms.

 

  1. If 16 g of oxygen contains 1 mole of oxygen atoms calculate the mass of one atom of oxygen in grams.

Answer: 1 mole (6.02×1023 atoms) of oxygen has mass = 16 gram.

1 atom of oxygen has mass = 16 / 6.02×1023

= 2.66 × 10-23 gram.

  1. How many times is 1 mole of oxygen atom heavier than 1 mole of hydrogen atom?

Answer: mass of 1 mole of oxygen is = 16 gram.

Mass of 1 mole of hydrogen = 1 gram.

 

So we can say that 1 mole of oxygen is 16 times heavier than 1 mole of hydrogen.

 

  1. Why does 10 g nitrogen gas contain the same number of molecules as 10 g of carbon monoxide?

Answer: molar mass of nitrogen gas( N2) and that of carbon monoxide (CO) is same, i,e 28 gram. That’s why 10 gram of nitrogen and 10 gram of carbon monoxide contains same number of molecules.

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