NAVODAYA VIDYALAYA SAMITI, NOIDA��E-CONTENT FOR CLASS XI��CHAPTER:1�SOME BASIC CONCEPTS OF CHEMISTRY

M.MUNENDRA KUMAR

PGT CHEMISTRY

JNV MAHABUBNAGAR TELANGANA

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IMPOTANCE OF CHEMISTRY

Chemistry is the branch of science that studies the composition, properties and interaction of matter. Chemists are interested in knowing how chemical transformations occur. Chemistry plays a central role in science and is often intertwined with other branches of science like physics, biology, geology etc. Chemistry also plays an important role in daily life.

Chemistry plays an important role in meeting

human needs for food, health care products

and other materials aimed at improving the

quality of life. This is exemplified by the large

scale production of a variety of fertilizers,

improved varieties of pesticides and

insecticides. Similarly many life saving drugs

such as cisplatin and taxol, are effective in

cancer therapy and AZT (Azidothymidine)

used for helping AIDS victims, have been

isolated from plant and animal sources or

prepared by synthetic methods.

NATURE OF MATTER

(i) Solids have definite volume and definite

shape.

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(ii) Liquids have definite volume but not the

definite shape. They take the shape of the

container in which they are placed.

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(iii) Gases have neither definite volume nor

definite shape. They completely occupy the

container in which they are placed.

INTERNATIONAL STANDARD UNITS

PREFIXES:

MASS & WEIGHT:

UNCERTAINITY IN MEASUREMENT

• Meaningful ways to handle the numbers conveniently and present the data realistically with certainty to the extent possible.

SCIENTIFIC NOTATION:

Chemistry deals with both smaller as well as large numbers ,this problem is solved by using EXPONENTIAL NOTATION.i.e N x10ⁿ

n can have both +ve & -ve values.,N is the number between 1.000.. and 9.999…

^Ex: 232.508 is written as 2.32508 X 10²,moving to left of the decimal exponent value will increase.

0.00016 is written as 1.6 x10 ^-4 ,moving to right of the decimal the exponential value will decrease.

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MATHEMATICAL OPERATIONS

MULTIPLICATION & DIVISION:

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• (5.6 X10⁵ )X (6.9X10⁸)

=(5.6 x6.9) x10 ⁵⁺⁸

=3.864 x10 ¹⁴

• 2.7 x 10^-3/5.5 x10 ⁴

=0.4909 x 10^-7

= 4.909 x10^-8

ADDITION AND SUBSTRACTION

• 6.65 x10⁴ and 8.95 x10 ³

Exponents should made same for both the numbers.

=6.65 x10⁴ + 0.895 x 10⁴

=7.545 x10⁴

• 2.5 x 10^-2 -4.8 x10^-3

= (2.5 x 10^-2 )-(0.48 x10^-2 )

=2.02 x10^-2

SIGNIFICANT FIGURES

• Precision refers to the closeness of various measurements for the same quantity.
• Accuracy is the agreement of a particular value

to the true value of the result.

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Significant figures are meaningful digits which are known with certainty. The uncertainty is indicated by writing the certain digits and the last uncertain digit. Thus, if we write a result as 11.2 mL, we say the 11 is certain and 2 is uncertain

RULES TO BE FOLLOWED:

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There are certain rules for determining the number of significant figures. These are stated below:

(1) All non-zero digits are significant. For example in 285 cm, there are three

significant figures and in 0.25 mL, there are two significant figures.

(2) Zeros preceding to first non-zero digit are not significant. Such zero indicates the

position of decimal point.

Thus, 0.03 has one significant figure and 0.0052 has two significant figures.

(3) Zeros between two non-zero digits are significant. Thus, 2.005 has four significant

figures

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(4) Zeros at the end or right of a number are significant provided they are on the right

side of the decimal point. For example, 0.200 g has three significant figures. But, if otherwise, the terminal zeros are not significant if there is no decimal point. For example, 100 has only one significant figure, but 100. has three significant figures and 100.0 has four significant figures. Such numbers are better represented in scientific notation. We can express the number 100 as 1×102 for one significant figure, 1.0×102 for two significant figures and 1.00×102 for three significant figures.

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(5) Counting numbers of objects, for example, 2 balls or 20 eggs, have infinite significant figures as these are exact numbers and can be represented by writing infinite number of zeros after placing a decimal i.e.,

2 = 2.000000 or 20 = 20.000000

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In numbers written in scientific notation, all digits are significant e.g., 4.01×102 has three significant figures, and 8.256 × 10–3 has four significant figures

ROUNDING OFF RULES:

1. If the rightmost digit to be removed is more than 5, the preceding number is increased by one. for example, 1.386 If we have to remove 6, we have to round it

to 1.39

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2. If the rightmost digit to be removed is less than 5, the preceding number is not changed.

For example, 4.334 if 4 is to be removed, then the result is rounded upto 4.33.

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3. If the rightmost digit to be removed is 5, then the preceding number is not changed if it is an even number but it is increased by one if it is an odd number. For example,

if 6.35 is to be rounded by removing 5, we have to increase 3 to 4 giving 6.4 as the

result. However, if 6.25 is to be rounded off it is rounded off to 6.2.

ATOMIC MASS

Today, ‘amu’ has been replaced by ‘u’

which is known as unified mass

MOLECULAR MASS:

Molecular mass is the sum of atomic masses of the elements present in a molecule. It is

obtained by multiplying the atomic mass of each element by the number of its atoms and

adding them together. For example, molecular mass of methane which contains one carbon

atom and four hydrogen atoms can be obtained as follows :

Molecular mass of methane,

(CH4) = (12.011 u) + 4 (1.008 u)

= 16.043 u

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FORMULA UNIT MASS:

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Formula mass instead of molecular mass as in the solid state sodium

chloride does not exist as a single entity.

Thus, formula mass of sodium chloride =atomic mass of sodium + atomic mass of chlorine

= 23.0 u + 35.5 u = 58.5 u

MOLE CONCEPT:

One mole is the amount of a substance that contains as many particles or entities as there are atoms in exactly 12 g (or 0.012 kg) of the 12C isotope. It may be emphasized

that the mole of a substance always contain the same number of entities, no matter what

the substance may be. In order to determine this number precisely, the mass of a carbon–

12 atom was determined by a mass spectrometer and found to be equal to 1.992648 × 10–23 g. Knowing that one mole of carbon weighs 12 g, the number of atoms in it is equal to :

= 6.022 X 10²³ atoms/mol .

This number of entities in 1 mole is so important that it is given a separate name and symbol. It is known as ‘Avogadro constant’,

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The mass of one mole of a substance in grams is called its molar mass.

������������1 MOLE OF ANY SPEICES=6.022 X10²³ NUMBER OF THAT SPECIES=MOLAR MASS IN GRAMS.������NOTE: Species can be atoms, molecules and ions.

MASS PERCENTAGE:

Empirical Formula for Molecular�Formula:

STOICHIOMETRY AND�STOICHIOMETRIC CALCULATIONS

CH₄ (g) + 2O₂ (g) −−🡪 CO₂ (g) + 2 H₂O (g)

Limiting Reagent:

The reactant which is present in the lesser amount gets consumed after sometime and after that no further reaction takes place whatever be the amount of the other reactant present. Hence, the reactant which gets consumed, limits the amount of product formed and is, therefore,

called the limiting reagent.

REACTIONS IN SOLUTIONS

• The concentration of a solution or the amount of substance present

in its given volume can be expressed in any of the following ways.

• 1. Mass per cent or weight per cent (w/w %)
• 2. Mole fraction
• 3. Molarity
• 4. Molality

MASS PERCENTAGE:

MOLE FRACTION:

MOLARITY:

MOLALITY:

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• THANK YOU
• M.MUNENDRA KUMAR
• PGT CHEMISTRY
• JNV MAHABUBNAGAR
• TELANGANA