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UNIT 1
SOME BASIC CONCEPTS OF CHEMISTRY
Chemistry: Chemistry is the branch of science that deals with the composition,
structure and properties of matter
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Inorganic Chemistry-This branch deals with the study of compounds of all
other elements except carbon
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Physical Chemistry-The explanation of fundamental principles governing
various chemical phenomena is the main concern of this branch
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Industrial Chemistry-The chemistry involved in industrial processes is studied
under this branch
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Biochemistry-This branch deals with the chemical changes going on in the
bodies of living organisms; plants and animals
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are studied under this branch
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These properties can be classified into two
categories – physical properties and chemical properties
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E
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colour, odour, melting
point, boiling point, density etc
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e
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Burning of Mg-ribbon in air
Chemical properties are characteristic reactions of different substances; these
include acidity or basicity, combustibility etc
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, are quantitative in nature
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The International System of Units (SI)
The International System of Units (in French Le Systeme International d’Unites–
abbreviated as SI) was established by the 11th General Conference on Weights and
Measures (CGPM from ConferenceGenerale des Poids at Measures)
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The mass of a substance is
constant whereas its weight may vary from one place to another due to change in
gravity
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So volume has units of m3 or cm3 or
dm3
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1 L = 1000 mL, 1000 cm3 = 1 dm3
Density: Density of a substance is its amount of mass per unit volume
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Temperature--There are three common scales to measure temperature — °C (degree
celsius), °F (degree Fahrenheit) and K (kelvin)
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K = °C + 273
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e
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Scientific Notation
In which any number can be represented in the form N × 10 n (Where n is an exponent
having positive or negative values and N can vary between 1 to 10)
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g
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508 as 2
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Similarly, 0
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6 x 10–4
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Accuracy is the agreement of a particular value to the true value of the result
Significant Figures
The reliability of a measurement is indicated by the number of digits used to
represent it
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These are called as Significant figures
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Rules for Determining the Number of Significant Figures
All non-zero digits are significant
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9 has two significant
figures, while 2
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The decimal place does not
determine the number of significant figures
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For
example, 2
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02 has three significant figures
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For example, 0
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0045has two significant figures
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For example, 16
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00has four significant figures
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In exponential notations, the numerical portion represents the number of
significant figures
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00045 isexpressed as 4
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The number of significant figures in this number is 2,
while inAvogadro's number (6
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The decimal point does not count towards the number of significant figures
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601 or 0
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45601 all having same number
ofsignificant figures
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1
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317 is
rounded off to 4
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2
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312 isrounded off to 4
...

3
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In case of even figure, the
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preceding digit remains unchanged
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375 is rounded off to 8
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365 is
rounded off to 8
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Dimensional Analysis During calculations generally there is a need to convert units
from one system to other
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For example- 5 feet and 2 inches (height of an Indian female) is to converted in SI
unit
1 inch = 2
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volume
Definite
2
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Inter molecular Very high
force of attraction
4
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Inter molecular Very small
space
7
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Expansion on Very little
heating
9
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Fluidity
Can’t flow
Can flow
10
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There
are 114 elements known to us, out of which 92 are naturally occurring while the rest
have been prepared artificially
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Compounds
A compound is a pure substance made up of two or more elements combined in a
definite proportion by mass, which could be split by suitable chemical methods
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The properties of compounds are totally different from the elements from
which they are formed
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Compounds are broadly classified into inorganic and organic compounds
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For example, common salt, marble and limestone
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They all contain carbon
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Mixtures
A mixture is a combination of two or more elements or compounds in any proportion
so that the components do not lose their identity
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Homogeneous mixtures have the same composition throughout the sample
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They are
also called solutions
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Heterogeneous mixtures consist of two or more parts (phases), which have different
compositions
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g
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LAWS OF CHEMICAL COMBINATIONS
Law of Conservation of Mass (Given by Antoine Lavoisier in 1789)
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Law of Definite Proportions or Law of Constant Composition:
This law was proposed by Louis Proust in 1799, which states that:
'A chemical compound always consists of the same elements combined together in
the same ratio, irrespective of the method of preparation or the source from where it
is taken'
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Gay Lussac’s Law of Gaseous Volumes (Given by Gay Lussac in 1808
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e
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H2(g) + Cl2(g) ---→2HCl(g)
1V 1V
2V
All reactants and products have simple ratio 1:1:2
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Dalton's Atomic Theory
All substances are made up of tiny, indivisible particles called atoms
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Atoms of different elements are different in all respects
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Atoms combine with each other in simple whole number ratios to form
compound atoms called molecules
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Atoms and Molecules
The smallest particle of an element, which may or may not have independent
existence is called an atom, while the smallest particle of a substance which is
capable of independent existence is called a molecule
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Homoatomic molecules
are made up of the atoms of the same element and heteroatomic molecules are made
up of the atoms of the different element have different atomicity (number of atoms in
a molecule of an element) like monoatomic, diatomic, triatomic and polyatomic
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And 1 amu = 1
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Today, ‘amu’ has been replaced by ‘u’ which is known as unified mass
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Gram Atomic Mass
The quantity of an element whose mass in grams is numerically equal to its atomic
mass
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For example, the atomic mass of oxygen = 16 amu
Therefore gram atomic mass of oxygen = 16 g
Molecular Mass
Molecular mass of a substance is defined as the average relative mass of its molecule
as compared to the mass of an atom of C-12 taken as 12
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For example, a molecule of carbon dioxide is 44 times heavier than 1/12th of the
mass of an atom of carbon
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It is obtained by adding the atomic masses of all the atoms present in one molecule
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In simple terms, molecular mass of a substance
expressed in grams is called gram molecular mass
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g
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It
is used for the ionic compounds
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Mole is defined as the amount of a substance, which contains the same number of
chemical units (atoms, molecules, ions or electrons) as there are atoms in exactly 12
grams of pure carbon-12
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022 x1023( Avogadro's number) chemical units
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Molar Volume
The volume occupied by one mole of any substance is called its molar volume
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One mole of all gaseous substances at 273 K and 1 atm pressure
occupies a volume equal to 22
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The unit of molar volume is litre
per mol or millilitre per mol
PERCENTAGE COMPOSITION—
The mass percentage of each constituent element present in any compound is called
its percentage composition
Mass % of the element=Mass of element in 1 molecule of the compound x 100
Molecular mass of the compound
Empirical Formula and Molecular Formula—
An empirical formula represents the simplest whole number ratio of various atoms
present in a compound
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g
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The molecular formula shows the exact number of different types of atoms present
in a molecule of a compound
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g
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Relationship between empirical and molecular formulae
The two formulas are related as Molecular formula = n x empirical formula

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Chemical EquationShorthand representation of a chemical change in terms ofsymbols and formulae of
the substances involved in the reaction is called chemical equation
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Limiting Reagent- The reactant which gets consumed first or limits the amount of
product formed is known as limiting reagent
Reactions in Solutions-- The concentration of a solution can be expressed in any of
the following ways
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Mass Percent is the mass of the solute in grams per 100 grams of the solution
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A 5 % solution of sodium chloride means that 5 g of NaCl is present in 100g
of the solution
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A 5 % (v/v) solution of ethyl alcohol contains 5 cm3 of alcohol in 100 cm3 of
the solution
3
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It isdenoted by the symbol M
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Molarity of the solution = No
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4
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Molality is expressed as 'm'
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Mole Fraction is the ratio of number of moles of one component to the total
number of moles (solute and solvents) present in the solution
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Mole fraction of the solute =
Moles of the solute
Moles of solute + Moles of solvent
Mole fraction of the solvent =

Moles of the solvent
Moles of solute + Moles of solvent

Mole fraction of the solute + Mole fraction of solvent = 1
One Mark questions with answers
1
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050 x 104?
Ans
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What is the S
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unit of Density?
Ans
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What do mean by Mole fraction?
Ans
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It is
expressed as 'x'
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Round off up to 3 significant figure (a) 1
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225
Ans
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24 (b) 1
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What is AZT?
Ans
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6
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The reactant which gets consumed first or limits the amount of product
formed is known as limiting reagent
7
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8
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One mole is the amount of a substance that contains as many particles as
there are atoms in exactly 12 g of the carbon-12
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Calculate the formula mass calcium chloride
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Formula mass of CaCl2= 40+2 x35
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What is the law called which deals with the ratios of the volumes of the
gaseous reactants and products?
Ans
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Two Marks questions with answers
1
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Ans
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Homogeneous
mixtures
1
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have different compositions
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These
mixtures
have
visible
2
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2
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Which law is illustrated by this
observation? State the law
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Law of Definite Proportions This law states that: A chemical compound
always consists of the same elements combined together in the same ratio,
irrespective of the method of preparation or the source from where it is taken
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Write the empirical formula of the following:
(a) N2O4
(b) C6H12O6 (c) H2O
(d) H2O2
Ans
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Briefly explain the difference between precision and accuracy
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Precision refers to the closeness of various measurements for the same
quantity
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5
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Explain it with one example
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When two elements combine to form two or more compounds, then the
different masses of one element, which combine with a fixed mass of the
other, bear a simple ratio to one another
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Compound
CO
CO2
Mass of C
12
12
Mass of O
16
32
Masses of oxygen which combine with a fixed mass of carbon (12g) bear a
simple ratio of 16:32 or 1:2
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Chlorine has two isotopes of atomic mass units 34
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97
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755 and 0
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Find the average atomic
mass of chlorine
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Average atomic mass = 34
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755 +36
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245 = 35
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Calculate the percentage composition of water
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Mass % of an element = mass of that element in the compound × 100
molar mass of the compound
Molar mass of water = 18
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008 × 100
18
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18
Mass % of oxygen = 16
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79

18
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State the number of significant figures in each of the following:
(i) 208
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00456 (iii) 453 (iv) 0
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(i) 208
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(ii) 0
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(iii) 453 has three significant figures
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346 has three significant figures
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Express the results of the following calculations to the appropriate number of
significant figures
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= 0
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0561
`
= 0
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3 x 10-4
9
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50 mol Na2CO3 and 0
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Molar mass of Na2CO3= 2 x 23 +12 + 3 x 16 = 106 g / mol
0
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50 x 106 = 53 g
0
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50 mol i
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53 g of Na2CO3 are present in I L of the
solution
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What is unit factor method? Express the following in SI units - 93 million
miles (distance between earth and sun)
Ans
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93 million miles = 93 x 106 miles
1 mile = 1
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60934 x 103 m

= 1
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Write the three points of difference between compound and mixture
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Compound
Mixture
Constituents are always present in a Constituents may be present in any
fixed ratio by mass
ratio
May or may not be homogeneous in Always homogeneous in nature
nature
Constituents can be easily separated Constituents cannot
be easily
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by simple mechanical means
separated by simple mechanical means
Properties are midway between those Properties are entirely different from
of its constituents
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3
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One million silver atoms weigh 1
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Calculate the gram atomic mass of silver
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atomic mass of an element expressed in grams is the gram atomic mass
Number of silver atoms = 1 million = 1 x 106
Mass of one million Ag atoms = 1
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023 x 1023 atoms of silver = 1
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023 x 1023
1 x 106
= 107
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What is the percentage of carbon, hydrogen and oxygen in ethanol?
Ans
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01 + 61
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00) g = 46
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02g / 46
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14%
Mass per cent of hydrogen = (6
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068g)×100 = 13
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00 g / 46
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73%
5
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Calculate the molarity of NaOH in the solution
prepared by dissolving its 4 g in enough water to form 250 mL of the solution
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The number of moles of solute dissolved per litre (dm3) of the solution is
called molarity
Since molarity (M) = No
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250 L
=(4 g / 40 g 0
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250L =0
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250 L
= 0
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4 M
6
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Pure substance- ethyl alcohol ,oxygen , carbon, distilled water
Mixture- blood, steel
7
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1
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If the digit involved is less than 5, it is neglected and the preceding
significant figure remains unchanged,
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3
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In case of even figure,
the preceding digit remains unchanged
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Define –(a) Average atomic mass (b) Molecular mass (c) Formula mass
Ans
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(b) Molecular mass- it is sum of atomic masses of the elements present in a
molecule
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9
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0048 (b) 234,000 (c) 200
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(a) 4
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3 x 105 (c) 2
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Calculate the number of atoms in each of the following (i) 52 moles of Ar
(ii) 52 u of He
(iii) 52 g of He
Ans
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022 × 1023 atoms of Ar
52 mol of Ar = 52 × 6
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131 × 1025 atoms of Ar
(ii)1 atom of He = 4 u of He
Or,
4 u of He = 1 atom of He
1 u of He = 1/4 atom of He
52u of He = 52/4 atom of He
= 13 atoms of He
(iii) Molar mass of He = 4 g/mol
4 g of He contains = 6
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022 × 1023 x 52 = 78
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What is the difference between empirical and molecular formula? A compound
contains 4
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27 % carbon and 71
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Its molar
mass is
98
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What are its empirical and molecular formulas?
Ans
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The empirical formula of the above compound is CH2Cl
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5 = 49
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96/49
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Dinitrogen and dihydrogen react with each other to produce ammonia
according to the following chemical equation:
N2(g) + H2(g) → 2NH3(g)
(i) Calculate the mass of ammonia produced if 2
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00 × 103 g of dihydrogen
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(i) Balancing the given chemical equation,
From the equation, 1 mole (28 g) of dinitrogen reacts with 3 mole (6 g) of
dihydrogen to give 2 mole (34 g) of ammonia
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00 × 103 g of dinitrogen will react with

dihydrogen i
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,

2
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6 g of dihydrogen
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00 × 103 g
Hence, N2 is the limiting reagent
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Hence, mass of ammonia produced by 2000 g of N2
= 2428
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Hence, H2 will
remain unreacted
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00 × 103 g – 428
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4 g
3
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Burning a small
sample of it in oxygen gives 3
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690 g of water and no
other products
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0 L (measured at STP) of this welding gas is
found to weigh 11
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Calculate (i) empirical formula, (ii) molar mass of the
gas, and (iii) molecular formula
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(i) 1 mole (44 g) of CO2 contains 12 g of carbon
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38 g of CO2 will contain carbon
= 0
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0
...
0767 g
Since carbon and hydrogen are the only constituents of the compound,
the total mass of the compound is:= 0
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0767 g= 0
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32%
Percent of H in the compound
= 7
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69
Moles of hydrogen in the compound =
= 7
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69: 7
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(ii) Given,
Weight of 10
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T
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6 g
Weight of 22
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984 g≈ 26 g
Hence, the molar mass of the gas is 26 g
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What is the difference between 160 cm and 160
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160 has three significant figures while 160
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Hence, 160
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2
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Methane is the limiting reactant because the other reactant is oxygen of the
air which is always present in excess
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3
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Their
relative number of moles in the compound are 1
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88
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Atomic masses of the elements A and B
b
...
Relative no
...
of moles
1
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88 = 16
Calculation of Empirical formula
Element Relative no
...
25
1
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25 = 1
2
B
1
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88/1
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5
3
Empirical formula = A2B3
Calculation of molecular formulaEmpirical formula mass = 2 x 56 + 3x 16 = 160
n= molecular mass / Empirical formula mass = 160/160 = 1
Molecular formula = A2B3

no
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