Study Portal 9 – Chapter 9

Introduction of Chemistry


Q1.      Fill In The Blanks.

  1. i) Physical chemistry deals with the study of physical aspects of matter.
  2. ii) The branch of chemistry in which the molecules of atom in studied is called Nuclear
    • A sample of pure substance having all atoms are alike is called an element.
  1. For the mass comparison of atoms, the standard atom chosen is C12.
  2. The number 6.0225×1023 is called Avogadro’s No.
  3. Two moles of water constitute 36g.
  • The process of formation of ions is called Ionization.
  • The atomic mass unit is expressed by the symbol m.u
  1. The molecular formula shows exact number and type of atoms.
  2. Glucose is polyatomic type of molecule.

Q2.      Tick the correct answer from the given list.

  1. i) The smallest component of an element that still retains properties of the element is called (a) Electron (b) Proton (c) Neutron (d) Atom .
  2. ii) The atom is a Greek word meaning:

(a) Indivisible                             (b) Small particle

(c) Which enter in reactions        (d) Basic particle.

  1. ii) The branch of chemistry which deals with determination of molecular formula is called:

(a) Nuclear chemistry                 (b) Organic chemistry

(c) Analytical chemistry            (d) Industrial chemistry

iii)     Empirical formula shows the:

(a) Ratio of atoms                      (b) Ratio of molecules

(c) Exact number of atoms         (d) Exact number of molecules

  1. Molecular mass is calculated by:

(a) Counting number of atoms of C12

(b) Taking sum of the masses of atoms in the molecules 

(c) By taking the sum of protons and neutrons number

(d) None of these

  1. The value of a.m.u in grams is:

(a) 1.6 ´ 1023                  (b) 1.6 ´ 1027

(c) 1.6 ´ 10-23                  (d) 1.6 ´ 10-24.

  1. The atoms can exists freely in nature:

(a) Always                                                          (b) Never

(c) Some exist and some do not  (d) None of these is true

  • The formula unit is used for the:

(a) Ionic substances                   (b) Molecular substances

(c) Mixture                                              (d) None of these

  • The gram atomic or molecular mass is called:

(a) One mole                              (b) Two moles

(c) Three moles                           (d) Four moles

  1. The concept of Avogadro’s number is used to calculate the:

(a) Number of atoms                  (b) Number of molecules

(c) Number of ions                     (d) All of these

Q3.      Answer the following questions in short.

  1. i) Why understanding of chemistry is important to us?

Ans.  The chemistry plays very important role in our life. It has a direct application in every sphere of our life. It is evident that the 21st century is the century of chemistry. So it is very important to understand the chemistry.

  1. ii) Give a short note on classification of matter.

Ans.  The matter is the substance that has mass. It is distributed all around us and this matter is classified into two main categories i.e. the pure substances and the mixture. A pure substance shows uniform properties every time. While in mixture the quantity of constituents can vary.

iii)     What is meant by the term atomic number?

Ans.  Atomic number is the identity number of an atom or element. It is equal to the number of protons found in the molecules of atom symbolized as “Z”.

  1. iv) How will you differentiate between the atomic mass number and the relative atomic mass?

Ans.  The sum of number of protons and neutrons in an atom is the atomic mass number symbolized as “A” and relative atomic mass is the mass of an atom or molecule which is obtained by comparing the mass of an atom or molecule with the standard C12.

  1. v) Distinguish among atoms and ions with examples.

Ans.  Atom is the smallest unit of matter which takes part in chemical reactions and shows all properties of an element e.g. if a piece of gold is divided into two fragments each fragments show the characters of gold. Ion when an atom of an element losses or gain the electron then it converted into ion. “cation” positive ion, “An-Ion” negative ion e.g. Na+, Cl.

  1. vi) Explain with an example how the molecular mass is calculated?

Ans.  The sum of atomic mass of atoms of each elements present in a molecule of the compound is known as molecular mass. It is the additive property because it is the sum of the individual atomic mass of different atom present in the molecule of compound e.g. HNO3 = (1 ´ 1) + (14 ´ 1) + (16 ´ 3) = 63a.m.u.

vii)    What are the different types of matter found in nature?

Ans.  There are two types of matter found in nature (a) Element (b) Compound

Element:- Element is a sample of pure substance that has all atoms with same atomic number.

Compound:- Compound is a sample of pure substance that has two or more than two types of elements.

viii)      What is mole?

Ans.  When atomic weight or molecular weight or formula weight of the substance expressed in gram is known as gram mole or simply mole.

  1. ix) What is meant by a.m.u?

Ans.  The atoms are very small and their mass unit is measured in a very small unit called atomic mass unit (a.m.u) in grams it is equal to 1 a.m.u = 1.6 ´ 1024g.

  1. x) Describe with example how simple inorganic compound named.

Ans.  The names of ionic compounds are written by listing the name of the positive ion first, followed by the name of the negative ion e.g. NaCl. KClO3

Q4.      Answer the following question with reasoning.

  1. i) How Avogadro’s number and the mole are related with each other?

Ans.  The atomic mass or molecular mass expressed in terms of grams is called one mole of that substance, and one mole of any substance contains 6.02×1023 particle (atoms/molecules) i.e. 1mole of “O” has 6.02×1023 atoms and 1mole of “H2O” has 6.02×1023 molecules. This number is called Avogadro’s number.

  1. ii) Comment that concepts of vital for chemists?

Ans.  The upper atmospheric of earth contains radicals which are formed there by the action of ultra vital radiation that is coming from sun and thus the energy of this highly injurious UV radiation is blocked and radicals play an important role in combustion, polymerization and many other processes including human physiology.

iii)     Distinguish between ion and free radical.

Ans.  An ion is an atom or group of atoms that has lost or gained one or more electrons. The ions are of two types by the charges negatively charged ions are called an ions and the positively charged are called cations. An ion consisting of multiple atoms is called a polyatomic ion. The radical are atomic or molecular species with unpaired electrons. The electron of the free radical is written by a dot upon the symbol of free radical.

  1. iv) What is the difference between empirical formula and formula unit?

Ans.  The empirical formula represents the simple ratio of the atoms present in a compound e.g. in glucose (C6H12O6) the simplest ratio of atoms is 1:2:1. some times a molecule exists as a large entity of particles, for case of simplest ratio of the formula of such large structure is written this simplest ratio is termed as formula unit e.g. sodium chloride written as “NaCl”.

  1. v) Why C12 is taken as the standard for calculating atomic molecular mass?

Ans.  If we analyzed a lump of pure carbon from the planet earth, it is observed that 98.9% of all carbon atoms are C12 atoms and 1.11% of all carbon atoms are C13 atoms. So 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. Based on carbon-12 standard, the mass of an atom of carbon is 12 and 1/12th of it comes to be one.

Q5.   Nicotine a deadly poison which is found in tobacco has the formula C10H14N2. An average cigarette contains 1mg of nicotine. What will be the number of molecules in this quantity?

C10H14N2 = [(10 ´ 12) + (14 ´ 1) + (14 ´ 2)]       = 162

As 1 mole of nicotine has 6.02×1023molecules   = 162g.

1 mole of C10H14N2                     = 162g  = 6.02 ´ 1023 molecules

And 1mg of C10H14N2 will have

= (6.02 ´ 1023 ´ 1atoms´1mg) / 162g C10H14N2

= (6.02 ´ 1023 ´ 1 ´ 103 g) / 162

= (602 x 10 2+233) / 162

= 3.716 – 1018 molecules.

Q6.      Calculate the molar mass of following.

(a) K2SO4                               (b) MnCl2                    (c) Al(OH) 3

(d) Fe (NO3) 3     (e) CuSO4. 5H2O

(a) K2SO4               = ( 39 ´ 2 ) + ( 32 ´ 1 ) + ( 16 ´ 4 )

= 78 + 32 + 64


(b) MnCl2               = ( 54.9 ´ 1) + ( 35.4 ´ 2 )

= 54.9 + 70.8

= 125.7 or 126

(c) Al(OH)= ( 27 ´ 1 ) + [ ( 16 + 1 )3 ]

= 27 + 17 ´ 3

= 27 + 51

= 78

(d) Fe (NO3) 3        = 56 + ( 14 + 16 ´ 3 ) ´ 3

= 56 + 62 ´ 3

= 56 + 186

= 242

(e) CuSO4. 5H2O   = [63.5 + 32 + 16 ´ 4] + [5 ´ ( 1 ´ 2 + 16 ´ 1)]

= 63.5 + 32 + 64 + 5 ´ 18

= 159.5 + 90

= 249.5

Q7.   Write down the molecular formula of the following compound.

(a) Ferrous Sulphate                    = FeSO4

(b) Ferric Sulphate                      = Fe2 (SO4)3

(c) Copper (II) Sulphides            = CuS

(d) Copper (I) Sulphate               = CuSO3

(e) Ammonium Bicarbonate       = NH4HCO3

Q8.   What are the mass and mole of sulphur in 50g of sulphuric acid?

Atomic or molecular mass of H2SO4=(1´2)+(32´1)+(16´4)= 98g

In 98g of H2SO4 mass of sulphur is  = 32

In 50g of H2SO4 mass of sulphur is        = 32 ´ 50 / 98

= 16.326g or 16.33g

Mole       = Given Mass / Molecular Mass   = 16.33 / 32

= 0.51mole

Q9.      Define chemistry? How chemistry effect our life?

“The branch of science which deals with the composition structure, properties and reactions of matter is called chemistry”.

The chemistry plays very important role in our daily life, it has a direct application in every sphere of our life, whether concerned to our food we eat, our homes we dwell, our cloth, our medicines, our entertaining materials, our educating books all are direct result of chemistry and chemistry is related with every discipline of our life. Without the applications of chemistry the life will be same as of the prehistoric or even below than that and knowledge and applications of chemistry are the basic constituent of our modern life.

Q10. Why the science is divided into various branches? Discuss the branches of chemistry in detail.

Today chemistry has a wide scope in all aspects of life and is serving the humanity day and night. Chemistry is divided into following main branches.

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.

Organic Chemistry:- Organic Chemistry is study of covalent compounds of carbon and hydrogen-hydrocarbons and their derivatives.

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

Biochemistry:-  It is the branch of chemistry in which we study the structure, composition and chemical reactions of substances founding living organism.

Industrial Chemistry:-  The branch of chemistry that deals with the manufacturing of chemical compounds on commercial scale is called industrial chemistry.

Nuclear Chemistry:-  Nuclear chemistry is the branch of chemistry that deals with the radioactivity nuclear process and properties.

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.

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

Q11. What is difference between the element, mixture and the compound?

Ans.  Elements:-  It is a substance made up of same type atoms, having same atomic number and it cannot be decomposed into simple substance by chemical means. It means that each element is made up of unique type of atoms that have very specific properties.

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 substance (compounds) that have entirely different properties. Compound can’t be broken down into its constituent elements by simple physical methods.

Mixture:-  When two or more elements or compounds mix-up physically without any fixed ratio, they form a mixture. The mixture can be separated into parent compounds by physical methods such as distillation, filtration, evaporation, precipitation, or magnetization. Mixtures that have uniform composition throughout are called homogenous mixture whereas heterogeneous mixtures are those in which composition is not uniform throughout.

Q.12.   What do you understand by the term symbol of an element? Explain various rules for assigning symbols to an element.

Ans.  The elements are represented by symbols which are abbreviations for the name of elements. 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 etc. in case of two letters symbol, only first letter is capital e.g. ‘Ca’ for calcium, ‘Na’ for sodium. In some cases, first and any other letter is used e.g. ‘Cl’ for chlorine and ‘Mg’ for magnesium etc.

Q.13.   What is the molecular formula of a compound? How the formulas are written?

Ans.  Compounds can be classified as ionic or covalent; the covalent compounds mostly exist in molecular form. A molecule is a true representative of the covalent compound and its formula is called molecular formula. e.g. H2O, HCl, H2SO4, CH4.

How to write chemical formula?  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+, Cl and O2-.
  • Valency of each ion is brought to the lower right corner of other ion by cross-exchange e.g.

NaCl                  Ca2+  Cl

NaCl                  Ca2+  Cl

NaCl                                  CaCl2

  1. If the valencies are same, they are offset and are not written in the chemical formula. But if they are different, they are indicated as such at the same positions.
  2. 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 represent the valency of the radical e.g. Al2(SO4)3 and Ca3(PO4)2

Q.14.   Discuss the concept of mole in chemistry? How it is related with the Avogadro’s number?

Ans.  The atomic mass, molecular mass or formula mass of a substance expressed in grams is called mole. Avogadro’s number is a collection of 6.02 x 1023 particles. It is represented by symbols ‘NA’ hence the 6.02 x 1023 number of atoms, molecules or formula units are called Avogadro’s number that is equivalent to one mole of respective substance.

Activity 1.2:- What are the empirical formula of benzene (C6H6), Sucrose (C12H22O11), Carbon dioxide (CO2) and Cellulose (C6H10O5).

Compound                                                                  Empirical Formula

Benzene (C6H6)                                                                       CH

Sucrose (C12H22O11)                                                     C12H22O11

Carbon dioxide (CO2)                                                  CO2

Cellulose (C6H10O5)                                                     C6H10O5

Activity 1.3:- Calculate the mass of the following compounds NaCl, CO2, C6H12O6, and Al(OH)3

NaCl    = 23 + 35.5                                                      = 58.5 a.m.u

CO2      = 12 + 16 ´ 2                                       = 44 a.m.u

C6H12O= (12 ´ 6) + (1 ´ 12) + (16 x 6)         = 72 + 12 + 96

= 180 a.m.u

Al(OH)3  = 27 + 3 (16 + 1)                               = 27 + 51

= 78 a.m.u

Activity 1.4:- Calculate the number of atoms in 100g of CO2 and Glucose C6H12O6.

As 1 mole of CO2 has 6.02 ´ 1023 molecule    = 44g

1 mole of CO2 = 44g   = 6.02 ´ 1023 molecule

44 g of CO2 has 6.02 x 1023 molecules and 6.02 ´ 1023 ´ 3 atoms

As one molecule of CO2 have 3 atoms.

(i)         100g of CO2 will have            = 6.02 ´ 1023 x 3 atoms ´ 100g CO2 /

44 g CO2

= 602 ´ 1023 ´ 3 / 44

= 41.04 ´ 1023

= 4.104 ´1024 atoms


(ii)        100 g of C6H12O6                    = (12 ´ 6) + (1 ´ 12) + (16 ´ 6)

= 72 + 12 + 96

= 180

As 1 mole of C6H12O6 has 6.02 ´ 1023 molecules        = 180g

180 g      = 6.02 ´ 1023 molecules.

And     100g of C6H12O6 has 24 atoms.

= 6.02 ´ 1023 ´ 24 atoms ´ 100g / 180 g

= 602 ´ 24 ´ 1023 / 180

= 8.027 ´ 1024 atoms

Example:- Calculate number of moles in 250 g of glucose.

Solution:- As the moles of glucose can easily be determined by using the formula.

Mole       = Given Mass / Atomic or molecular mass

The molecular mass of glucose (C6H12O6)

C =  6 ´ 12.01     = 72.06

H            =  12 ´ 1.0076 = 12.0912

O            =  6 ´ 16                      = 96.00

Total       = 72.06 + 12.0912 + 96.00

= 180.15

Mole       = 250 / 180.15

= 1.39 moles

Example:- Calculate total number of atoms into g of water.

Solution:-  As 1 mole of water has 6.02 ´ 1023 molecule        = 18g

1 mole of H2O                = 18g   = 6.02 ´ 1023 molecules

18g of H2O has 6.02 ´ 1023 molecules and 6.02 ´ 1023 ´ 3 atoms.

One molecule of H2O has 3 atoms.

And 1 g of H2O will have           = 6.02 ´ 1023 ´ 3 ´ 1 / 18

= 1.003 ´ 1023 atoms.

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