NOTES OF CHEMISTRY FOR CLASS IX SCIENCE

NOTES OF CHEMISTRY FOR CLASS IX SCIENCE

1. TEMPERATURE
Degree of hotness or coldness of a body is called "TEMPERATURE". "Temperature is a measure of the intensity of heat". Temperature is defined as : "the average kinetic energy of the molecules of a body is called temperature"
SCALES OF TEMPERATURE:
There are three scales of temperature. 1. Celsius or centigrade scale C. 2. Fahrenheit scale F. 3. Kelvin or Absolute scale K.
CONVERSION
Centigrade & kelvin
T_k = T_c + 273
Centigrade & Fahrenheit
C/5 = (F-32) /9
2. VOLUME
Volume is defined as " The space occupied by An object is called its volume."
SYMBOL
Volume is denoted by "V
UNITS
a) Cubic meter b) Liter c) cm³ d) mm³ e) Millilitre f) dm³
3. MASS
The quantity of matter contained in a body is called its "Mass".
SYMBOL
Mass is denoted by "m".
UNITS
a) Kilogram b) Gram c) Milligram d) Microgram
4. DENSITY
Mass per unit volume of a substance is called its "Density". OR Mass of one dm³ or one m³ or one cm³ of a substance is called its density.
FORMULA

UNIT
a) Kg / m³ b) gm / cm³ c) gm /litre d) gm / dm³
5. MOLE
"Atomic mass or formula mass or molecular mass of a substance expressed in grams is called MOLE". Or Mass of substance contains 6.02 x 10²³ atoms or molecules or ions is called "mole"
For example: 1. Atomic mass of carbon = 12 a.m.u. therefore 12 gram of carbon = one mole of carbon. 2. Formula mass of Nacl = 58.5 a.m.u. therefore 58.5 gm of Nacl = 1 mole of Nacl. 3. Molecular mass of CO = 28 a.m.u. therefore 28 gm of CO = I mole of CO
FORMULA
Number of moles = mass of substance(in grams) / molecular or atomic or formula mass of substance
6. AVOGADRO'S NUMBER
One mole of any substance contains 6.02 x 10²³ atoms, molecules or ions. This particular number is called "AVOGADRO'S NUMBER". It is denoted by NA. For Example. 1 mole carbon = 6.02 x 10²³ carbon atoms. 1 mole Na+ = 6.02 x 10²³ Na+ ions. 1 mole H2O = 6.02 x 10²³ H2O molecules.
7. LAW OF DEFINITE PROPOTION
STATEMENT
According to the law of definite propotion
"Every sample of pure substance always contains same elements in fixed propotion regardless of its method of preperation"
EXPLANATION
We can obtain or prepare water by a number of methods but water obtained from any source always contain 11.11% hydrogen and 88.88% oxygen. Similarly CO2 can be prepared by different methods but each sample of CO2 contains C=27.27% and O=72.72%.
8. SPECIFIC GRAVITY
Specific gravity of a substance is defined as the ratio of the mass of substance to the mass of an equal volume of water at a particular temperature.
FORMULA
Specific gravity = mass of substance / mass of an equal volume of water
UNIT
It has no unit.
9. GRAM ATOMIC MASS
"Atomic mass of an element expressed in gram is called gram atomic mass"
For example: Gram atomic mass of C=12gm. Gram atomic mass of H=1 gm. Gram atomic mass of O=16 gm.
10. GRAM MOLECULAR MASS
"Molecular mass of a molecule expressed in gms is called gram molecular mass."
For example: Gram molecular mass of hydrogen gas=2 gm. Gram molecular mass of oxygen gas =32gm. Gram molecular mass of HCl = 36.5 gm
11. ELEMENT
"Element is defined as a pure substance in which all the atoms have same chemical properties and have same atomic number"
For example: Carbon, sodium, hydrogen, chlorine, copper, gold, iron e.t.c.
TYPES OF ELEMENTS
Elements can be divided into two classes. 1. Metals. 2. Non-Metals.
METALS
They have shine on their surface. They are good conductors of electricity and heat. They reflect light. Metals are ductile. Metals are malleable.
EXAMPLE
Cu, Fe, Au, Na, Ca e.t.c.
NON-METALS
They have dull surface. They are bad conductors of electricity and heat. Non-metals are non ductile. They cannot be drawn into sheets. They are brittle. EXAMPLE H2, C, Cl2, O2, N2 e.t.c.
12. VALENCY
Valency is defined as
"the combining capacity or combining power of an element with other element"
In other words Valency may be defined as: the number of H-atoms which combine with or displace one atom of an element or a radical.
EXAMPLES
ELEMENT	VALENCY
Na, K	1
Ca, Mg	2
F, Cl	1
N	3
13. MOLECULE
The smallest unit of an element or compound, which can exist independently, is called "molecule".
14. EMPIRICAL FORMULA
"Empirical Formula is that formula which expresses the relative number of each kind of atoms present in the molecule of a compound" OR "The formula of a compound which expresses the ratio in which atoms of different elements are combined in a molecule"
Empirical formula only indicates atomic ratios but it does not indicate actual number of atoms of different kinds present in the molecule of a compound. Two or more compound may have same empirical formula. Empirical formula is determined by experiment.
EXAMPLE
Empirical Formula of Benzene = CH. Empirical Formula of Glucose = CH₂O

MOLECULAR FORMULA

The molecular formula of a compound is defined as:
"The formula of a compound which not only expresses the relative nummer of atoms of each kind but also expresses the actual number of atoms of each element present in one molecule".

Molecular formula and empirical formula of a compound are related as:
MOLECULAR FORMULA = (EMPIRICAL FORMULA)_n

Where "n" is an integer and is given by:

n = molecular mass of compound / Empirical formula mass of compound

Molecular formula of propane = C₃H₈.
Molecular formula of sugar = C₁₂H₂₂O₁₁.

SYMBOL

A symbol is an abbreviation for the chemical name of an element

A symbol represents only one atom of an element.

FOR EXAMPLE:
Carbon = C, Hydrogen= H, Chlorine = Cl, Gold = Au, Silver = Ag, Sodium = Na, bismuth = Bi etc.

FORMULA

The representation of molecule of a substance or compound in
the form of symbols is called "formula".

   With the help of formula we can find.
   (1) Name of elements present in the molecule.
   (2) Number of atoms of each element.
   (3) Composition of compound.

EXAMPLE:
NH₃, CO₂, CaCO₃, H₂O, H₂SO₄ etc.

COMPOUND

"Compounds are pure substances, which consist of two or more elements
combined chemically in a fixed ratio."

Compounds always have a definite composition.

EXAMPLE:
H₂SO₄, CaCl₂, H₂O, CO₂ etc.

MIXTURE

"A mixture is a substance, which consists of two or more pure substances
not chemically combined with each other in a definite composition ."

Mixtures do not have definite composition.

EXAMPLE:
Air, soil, brass ( cu + zinc) etc.

DIFFERENCE BETWEEN COMPOUND AND MIXTURE

	COMPOUND	MIXTURE
1.	It is a pure substance.	It is an impure substance.
2.	It can not be separated by physical method.	It can be separate by physical method.
3.	Element loose their properties in a compound.	Substances forming mixture retain their properties.
4.	Its composition is fixed throught its mass.	It has no fixed composition.
5.	It has fixed melting point.	It has no sharp melting point.

TYPES OF MIXTURE:
There are two types of mixture: (1) Homogenous mixture. (2) Heterogeneous mixture.
HOMOGENEOUS MIXTRE
A homogeneous mixture is defined as "the mixture, which has uniform composition throughout its mass".
EXAMPLE: Air, sugar solution, salt solution, alloys, soft drinks (Pepsi, coca-cola etc.)
HETEROGENEOUS MIXTURE
"The mixture that do not have uniform composition throughout its mass is known as heterogeneous mixture".
EXAMPLE: Soil, rocks etc.
MATTER
Any substance which possesses mass and occupies space is called "MATTER".
Matter is the stuff of which our whole universe is made. All matter on the earth is composed of either pure substance or a mixture of substances.
VARIABLE VALENCY
Many elements exhibit more than one valency which is known as variable valency.
EXAMPLE: Iron = Ferrous(+2), ferric (+3) Copper = Cuprous (+1),cupric (+2) Mercury = Mercurous (+1), mercuric (+2)
MOLECULAR MASS
The molecular mass of an element when it exists in the form of molecular or a compound in defined as the average mass of the molecule as compared to one atom of ₆C¹². OR The sum of atomic masses of all the atoms present in one molecules of a substance is called "molecular mass".
CHEMISTRY
Chemistry is the branch of science which deals with the properties, composition and structure of matter. Study of chemistry also includes the laws and principles related to the structure and inter-relations of elements and compoundes. Chemistry has the task of investigating the materials of which our universe is made.Chemistry investigates chemical changes, conditions under which chemical changes occur.Chemistry also deals with the way in which similar changes can be brought about in laboratory and on a large scale in industries. Chemistry is a very vast field.Chemistry is divided into a number of branches such as Organic chemistry, Inorganic chemistry, Physical chemistry, biochemistry, Applied chemistry, Nuclear chemistry etc.