BASIC CONCEPT OF CHEMISTRY
INTRODUCTION
Ø The word chemistry has been derived from Egyptian word “CHEMEA” which means
Black Colour.
Ø Chemistry concerns itself with the composition properties, constitutions and mutual
interactions of different kinds of matter.
SYMBOLS, ELEMENTARY FORMULA
SYMBOLS :
Ø Just as a steno uses shorthand to save time in taking down notes from his officer, in the
same manner a chemist, instead of writing full and lengthy names of elements, uses
certain abbreviations called symbols.
Ø A symbol represents one atom of an element and is usually the first letter of the name
of the element. Example – O – oxygen, N – Nitrogen, H – Hydrogen, S – Sulphur.
Ø When two or more elements begin with the same letter, another characteristic letter
from its name is added in order to avoid confusion Carbon – C, Calcium – Ca,
Cadmium – Cd, Cobalt – Co.
Ø The first letter is always capital and the second is always small.
Ø The abbreviations used for the lengthy names of elements are termed symbols.
ELEMENTARY FORMULA :
Ø You know that English alphabet has 26 letters. By combining these 26 letters we can
make millions of English Words.
Ø Much the same way, by combining elements in different combinations, we can make
an endless number of compounds.
Ø Each compound is represented by a formula.
Ø A symbolic representation of one molecule of a compound representing the number
of atoms of various elements present in it, is called formula of the compound.
Formula of Some Common compounds
1. Hydrochloric acid HCl
2. Nitric acid HNO3
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3. Sulphuric Acid H2SO4
How to read information in the formula of a compound?
(i) The symbols in a formula can be prefixed or suffixed by a numeral. When the numeral is
written on the left hand side before the formula, it represents number of molecules of the
compound, and hence, the number of atoms present in each molecule.
Following examples will make it clear :
(a) When we write 2S, 3Cl or 4Al, it means two atoms of sulphur; three atoms of chlorine or
four atoms of aluminium respectively.
(b) When we write 2NaCl, 4ZnO, etc. it means two molecules of sodium chloride (which
contains two atoms of sodium and two atoms of chlorine), four molecules of zinc oxide
(which contains four atoms of zinc and four atoms of oxygen).
(ii) When the numeral is written on the right bottom side of the symbol, it represents the number
of atoms in one molecule of a compound.
Following examples will make it clear :
(a) When we write H2, O2 etc., it means that one molecule of hydrogen has two atoms in it.
Similarly, one molecule of oxygen has two atoms in it.
(b) When we write SO2, it means one molecule of sulphur dioxide has one atom of sulphur and
two atoms of oxygen.
(c) When we write Al2(SO4)3, it means a molecule of aluminium sulphate has two atoms of
aluminium, three atoms of sulphur and twelve atoms of oxygen.
(d) When we write 3KNO3, it means there are three molecules of potassium nitrate.
Furthermore, total number of various atoms in three molecules are : three atoms of
potassium; three atoms of nitrogen and nine atoms of oxygen.
Illustrations –1: (i) What is the symbol of Copper?
Solution: Cu
(ii) What is the symbol of Sodium?
Solution : Na
(iii) What is the formula of Sodium hydroxide?
Solution : NaOH
ACID AND BASE
ACID :
Ø The word acid comes from the latin word “ACERE” which means sour.
Ø Curd, lemon, orange and vinegar taste sour. These substance taste sour because they contain
acids.
Ø A substance which dissolves in water to furnish H+ ions is called acid.
2 H O
HCl H Cl+ -
+
2 H O 2
2 4 4 H SO 2H SO+ -
+
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Name of acid Found in
Acetic acid Vinegar
Formic acid Ant’s sting
Citric acid Citrus fruits such as oranges, lemons, etc.
Lactic acid Curd
Oxalic acid Spinach
Ascorbic acid (Vitamin C) Amla, Citrus fruits
Tartaric acid Tamarind, grapes, unripe mangoes, etc.
Basicity of an acid
The number of hydrogen ions (H+) furnished by one molecule of an acid, on dissolving in
water, is called basicity of an acid.
Example :
One molecule of hydrochloric acid furnishes one hydrogen ion, therefore, its
basicity is 1. In other words, hydrochloric acid is monobasic acid.
Strong and weak acid
All the acid can be divided into two groups
(1) Strong acid (2) Weak acid
(1) Strong acids : Acids which are almost completely ionized in water are known as strong
acids
(2) Weak acids : Acids which are weakly ionized in water are known as weak acids.
List of strong acids and weak acid
Strong acid Weak acid
Sulphuric acid – H2SO4 Carbonic acid – H2CO3
Hydrochloric acid – HCl Sulphurous acid – H2SO3
Nitric acid – HNO3 Nitrous acid – HNO2
General physical properties of acids :
1. They have a sour taste.
2 H O
Chloride ion Hydrochloric acid Hydrogen ion
HCl H Cl+ -
+
( ) ( ) ( ) 2 H O
HCl H aq. Cl aq.+ -
¾¾¾ ® + !
( ) ( ) ( ) 2 H O 2
2 4 4 H SO 2H aq. SO aq.+ -
¾¾¾ ® + !
( ) ( ) ( )2 H O
3 3 CH COOH CH COO aq. H aq.- +
+ !
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2. They turn blue litmus solution red.
3. They turn methyl orange solution pink.
4. They do not affect phenolphthalein solution.
General chemical properties of acids :
1. Action with metals : Metals displace hydrogen from the acids. It has been found that
when metals like magnesium, aluminium, zinc and iron are treated with dilute
hydrochloric acid or dilute sulphuric acid, they displace hydrogen.
Examples : Metal + acid (dil.) ® Metal salt + Hydrogen
2. Action with metallic oxides : All dilute mineral acids (sulphuric acid, hydrochloric
acid and nitric acid), react with all metallic oxides to form their respective metallic salts
and water only.
Example : Metallic oxide + acid (dil.) ® Metallic salt + Water
CaO+2HNO3 ® Ca(NO3)2 + H2O
3. Action with metallic hydroxides : All dilute mineral acids react with all metallic
hydroxides to form their respective metallic salts and water only.
Example : Metallic hydroxide + Acid (dil.) ® Metallic salt + water
2NaOH + H2SO4 ® Na2SO4 + 2H2O
Uses of acids :
(a) Sulphuric acid :
(i) It is used in the manufacture of fertilizers.
(ii) It is used in car batteries.
(iii) It is used in the manufacture of dyes, drugs, paints, plastics, detergents etc.
(b) Hydrochloric acid
(i) It is used for cleaning metal surfaces during tinning and galvanizing.
(ii) It is used in dyeing industry.
(iii) It is used for preparing glucose from starch.
(c) Tartaric acid
It is used in the manufacture of baking powder.
BASE :
Ø Substance which are bitter in taste and feel soaps on touching are known as bases.
Ø A substance which dissolves in water to furnish ions is called base.
(i) All oxides of metals are bases.
(ii) All hydroxides of metals are bases.
2 4 4 2 Zn H SO ZnSO H + ® +
OH-
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Example :
(a) Alkalies : All bases which are soluble in water are called alkalies. This special name
given to the bases indicates that they are soluble in water.
Sodium hydroxide – NaOH , Potassium hydroxide – KOH
Acidity of an Bases
The number of replaceable hydroxyl groups present in a base which it can release when
dissolved in water or in aqueous solution as ions
Example : NaOH, KOH – Monoacid base
Ca(OH)2 – Diacid Base
Al(OH)3 – Triacid Base
Name of base Found in
Calcium hydroxide Lime water
Ammonium hydroxide Window cleaner
Sodium hydroxide / Potassium hydroxide Soap
Magnesium hydroxide Milk of magnesia
Strong Base and Weak Base
All the bases can be divided into two groups
(1) Strong bases (2) Weak bases
(1) Strong bases : A base which is completely ionizes in water and thus produces a large
amount of hydroxide ion (OH–) is called strong base, as NaOH, KOH
(2) Weak Base : A base which is partially ionized in water and thus produces a small
amount of hydroxide ion is called weak base, as NH4OH, Ca(OH)2
General physical properties of Bases :
1. Taste : All bases/ alkalis have a bitter taste.
2. Slippery touch : All bases/ alkali solutions have a slippery touch, much like that of
soap. Sometimes we say that alkalis have a soapy touch.
3. Corrosive action : The bases / alkalis, on in contact with skin, produce very painful
blisters. Sodium hydroxide and potassium hydroxide are extremely corrosive in nature
and should not be touched with bare hands.
4. Action with indictors : The action of indicators is shown in the following table :
Indicator Change in colour
Litmus From red to blue
Methyl orange From pink to yellow
Phenolphthalein From colourless to pink
2 H O
NaOH Na OH+ -
¾¾¾ ® +
2 H O
KOH K OH+ -
¾¾¾ ® +
( ) OH-
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General chemical properties of Bases :
1. Action with heat :
(a) Sodium hydroxide (NaOH) and potassium hydroxide (KOH) do not decompose on
heating. However, they melt, when strongly heated.
(b) Ammonium hydroxide decomposes rapidly on warming to form ammonia gas and
water.
(c) All other metallic hydroxides decompose on strong heating to form their respective
metallic oxides and water.
Examples : Metallic hydroxide Metallic oxide + Water
2. Action with Acids : All acids react with base to form salt and water as the only
products.
Uses of bases / alkalis :
1. Caustic soda and caustic potash
(a) They are extensively used in the manufacture of soap from vegetable.
(b) They are used in paper pulp from wood.
(c) They are used for making artificial fibres such as rayon, nylon, etc.
(d) They are used in the manufacture of medicines.
2. Calcium oxide and Calcium hydroxide
(a) They are used for neutralization of acidity of the acidic soils.
(b) Calcium hydroxide is used for removing hair from the animal skins.
(c) Calcium hydroxide is used for preparing bleaching powder.
3. Magnesium hydroxide and Aluminium hydroxide
They are used as antacids for relieving acidity in the stomach.
Illustrations –2: (i) HCl is a Monobasic or Dibasic
Solution: Monobasic
(ii) H2SO4 is a strong acid or weak acid.
Solution: Strong acid
(iii) KOH is a strong base or weak base.
Solution: Strong base
warm
4 3 2
Ammonium hydroxide Water Ammoniagas
NH OH NH H O ¾¾¾® +
heat
¾¾¾ ®
( ) heat
2 2 Calcium oxide Water Calcium hydroxide
Ca OH CaO H O ¾¾¾ ® +
( ) heat
2 2 Copper oxide Water Copper hydroxide
Cu OH CuO H O ¾¾¾ ® +
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SALT AND INDICATORS
SALT :
Ø A substance formed by the neutralization of an acid with a base is called salt.
Example : Acid + Base ® Salt + Water
Kinds of salts
All the salts can be divided into three groups
(1) Normal salts (2) Acid salts (3) Basic salts
(1) Normal salts : A salt formed by the complete replacement of the hydrogen ions (H+)
of an acid with metal ions (or positively charged ions) is called normal salt.
Example : Sodium chloride (NaCl), Potassium Chloride (KCl), Lead sulphide (PbS)
(2) Acid Salts : A salt formed by the partial replacement of H+ ions of an acid from its
molecule, with metal ions, is called acid salt.
Preparation and properties of Salts :
(a) Preparation of salts :
A salt is formed from an acid when a metal takes the place of hydrogen in acids.
The metals can take the place of hydrogen when the acids react chemically with the
following
(i) Metal hydroxides
(ii) Metal oxides
(iii)Metal carbonates
(iv) Active metals such as magnesium, zinc, etc.
(b) Properties of salts :
(i) Most of the salts are solids with high melting points and boiling points.
(ii) Salts are usually soluble in water. However, salts like carbonates, oxides and
sulphates are generally insoluble in water.
(iii)Salt solutions in water are good conductors of electricity.
(iv) Crystals of some salts have some fixed number of water molecules attached to
them. Such salts are called hydrated salts and the water molecules attached to them
are called water of crystallization.
Uses of salts in daily life :
1. Common salt : (NaCl) : It is used amount as table salt. It is used for preservation of
food in pickling. It is used to preserve raw hides. It is used in the manufacture of
chemical such as chlorine and caustic soda (NaOH).
2 4 2 4 2
Sodium hydroxide Sulphuric acid Sodium sulphate water
H SO 2NaOH Na SO 2H O + ¾¾ ® +
2 4 4 2
Sodium hydroxide Sulphuric acid Sodium hydrogen sulphate Water
NaOH H SO NaHSO H O + ¾¾ ® +
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2. Baking Soda : (NaHCO3) : It is used for making baking powder. It is used for
preparing antacid tablet, for controlling acidity of stomach.
3. Washing soda : (Na2CO3.10H2O) : It is used by washermen to wash clothes. It is used
in manufacture of glass and caustic soda. It is used in fire extinguishers. It is used in the
manufacture of detergents.
4. Green vitriol : (FeSO4.7H2O) : It is used in making blue inks and incurring leather.
5. Plaster of Paris : (CaSO4.1/2H2O) : It is used for making statues. It is used for setting
broken bones.
INDICATORS :
Ø A Special type of substances are used to test whether a substance is acidic or basic. These
substances are known as indicators.
Ø The indicators change their colour when added to a solution containing an acidic or basic
substances.
Ø Turmeric, Litmus, China rose petals etc., are some of the naturally occurring indicators.
Ø Indicators are basically coloured organic substances extracted from different plants
Illustrations –3: (i) The chemical name of marble is
Solution: Calcium carbonate
(ii) Plaster of paris is made from
Solution: Gypsum
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KEY POINTS
Ø The abbreviations used for the lengthy names of elements are termed symbols.
Ø Symbolic expression for a molecule is called a formula.
Ø Acids are sour in taste. Bases are bitter in taste and soapy to touch.
Ø Acid turns blue litmus red. Bases turn red litmus blue.
Ø An acid and a base neutralize each other and form a salt. A salt may be acidic, basic or
neutral in nature.
Ø Solutions of substances that show different colour in acidic, basic and neutral solutions are
called indicators.
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ASSIGNMENT – I
1. The abbreviation used for the lengthy name of an element is termed
(A) Formula (B) Valency
(C) Symbol (D) Radicals
2. The symbolic expression for a molecule is called
(A) Formula (B) Valency
(C) Symbol (D) Radicals
3. What is the symbol of Cobalt?
(A) Co (B) Cd
(C) Cl (D) Ca
4. What is the symbol of Antimony?
(A) As (B) At
(C) Al (D) Sb
5. What is the symbol of Lead?
(A) La (B) Le
(C) Pb (D) As
6. What is the symbol of Mercury?
(A) Mg (B) Mn
(C) Hg (D) Ag
7. What is the symbol of Silver?
(A) Si (B) Sl
(C) Ag (D) Au
8. What is the symbol of Gold?
(A) Go (B) Ga
(C) Gl (D) Au
9. What is the formula of sulphur dioxide?
(A) SO3 (B) SO2
(C) SO4 (D) CO2
10. What is the formula of water?
(A) K2O (B) H2O
(C) HCl (D) H2S
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ASSIGNMENT – II
1. The term ‘Acere’ means?
(A) Biffer (B) Sweet
(C) Sour (D) none of these
2. Citric acid found in
(A) Orange (B) Curd
(C) Spinach (D) Grapes
3. Tartaric acid found in
(A) Orange (B) Lemon
(C) Amla (D) Grapes
4. Calcium hydroxide present in
(A) Soap (B) Window clearner
(C) Lime water (D) none
5. Magnesium hydroxide present in
(A) Lime water (B) Milk of magnesia
(C) Soap (D) None
6. Ammonium hydroxide present in
(A) Lime water (B) Window cleaner
(C) Soap (D) None
7. Ammonium hydroxide and copper hydroxide are
(A) Strong acids (B) Weak acids
(C) Weak bases (D) Strong bases
8. The strongest base that can exist in aqueous solution is
(A) NH4+ (B) Cl–
(C) (D)
9. NaOH is a
(A) Strong acid (B) Strong base
(C) Weak acid (D) Weak base
10. Al(OH)3 is a
(A) Monoacid base (B) Diacid base
(C) Triacid base (D) none
OH- 2 H F+
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ASSIGNMENT – III
1. Epsom salt is
(A) Copper sulphate (B) Ferrous sulphate
(C) Magnesium sulphate (D) Calcium sulphate
2. Marble is
(A) Copper sulphate (B) Calcium carbonate
(C) Zinc sulphate (D) Calcium sulphate
3. White vitriol is
(A) Copper sulphate (B) Zinc sulphate
(C) Calcium sulphate (D) Calcium carbonate
4. In which of the following is used for washing clothes
(A) NaHCO3 (B) NaCl
(C) Na2CO3. 10H2O (D) CaCO3
5. In which of the following is used for making baking powder :
(A) NaCl (B) NaHCO3
(C) Na2CO3.10H2O (D) CaCO3
6. Plaster of paris is made from
(A) Lime stone (B) Slacked lime
(C) Quick lime (D) Gypsum
7. The chemical name of common salt
(A) Calcium chloride (B) Sodium chloride
(C) Calcium carbonate (D) Calcium sulphate
8. The colour of copper sulphate (CuSO4.5H2O)
(A) Green (B) Red
(C) Orange (D) Blue
9. The colour of Iron sulphate (FeSO4.7H2O)
(A) Red (B) Orange
(C) Blue (D) Green
10. The colour of zinc sulphate (ZnSO4.7H2O)
(A) Red (B) Blue
(C) White (D) Green
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KEY & HINTS
BASIC CONCEPT OF CHEMISTRY
ASSIGNMENT – I
1. (C)
2. (A)
3. (A)
4. (D)
5. (C)
6. (C)
7. (C)
8. (D)
9. (B)
10. (B)
ASSIGNMENT – II
1. (C)
2. (a)
3. (D)
4. (C)
5. (B)
6. (B)
7. (C)
8. (C)
9. (B)
10. (C)
ASSIGNMENT – III
1. (C)
2. (B)
3. (D)
4. (C)
5. (B)
6. (D)
7. (B)
8. (D)
9. (D)
10. (C)
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