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SOME BASIC CONCEPTS OF CHEMISTRY
Introduction:
Chemistry is the science of molecules and their transformations which deals with the
study of matter, its composition, the changes that matter undergoes and the relation
between changes in composition and changes in energy
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Branches of Chemistry:
 Organic Chemistry- This branch deals with study of carbon compounds especially
hydrocarbons and their derivatives
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It largely concerns itself with the study of minerals found
in the Earth's crust
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It is basically concerned
with laws and theories of the different branches of chemistry
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Analytical Chemistry-This branch deals with the qualitative and
quantitative analysis of various substances
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 Nuclear Chemistry- Nuclear reactions, such as nuclear fission, nuclear fusion,
transmutation processes etc
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Importance of Chemistry:
Chemistry plays a central role in science and is often intertwined with other branches of
science
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, including new material
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It also plays an important role in meeting human needs for
food, healthcare products and other material aimed at improving the quality of life
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For example, book, pen, pencil, water, air, all living beings, etc
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It is made up of only one type of atoms, ex
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Compound
Compound is the substance which is made up of two or more elements combined
together in a fixed ratio by their weight e
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, carbon dioxide
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e
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, Sugar + Water, Sodium Chloride + Water, Sand + Water
On the basis of composition, mixtures are of following type:
➢​ Homogeneous mixture: The mixture which has uniform composition through out e
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,
sugar solution
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e
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sand in water
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Atom word means not to be cut
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International System of Units (S
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)
The international system of units (in French Le Systeme International d' Unités abbreviated as SI) was established in 1960 by the 11th general conference on weights
and measures
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Prefixes in SI system
Definition of SI Base Units
●​ Metre: The metre is the length of the path travelled by light in vacuum during a time
interval of 1/(299792458) of a second
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●​ Second: The second is the duration of 9192631770 periods of the radiation
corresponding to the transition between the two hyperfine levels of the ground
state of the caesium-133 atom
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●​ Kelvin: The kelvin, unit of thermodynamic temperature, is the fraction 1/273
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●​ Mole: The mole is the amount of substance of a system which contains as many
elementary entities as there are atoms in 0
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●​ Candela: The candela is the luminous intensity, in a given direction, of a source
that emits monochromatic radiation of frequency 540 × 1012 hertz and that has a
radiant intensity in that direction of 1/683 watt per steradian
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Scientific
notations, significant figures and dimensional analysis help us in many ways in
presenting of data and theoretical calculations
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Thus, 232
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32508 × 102 in scientific notation
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However, accuracy is the agreement of a particular value to the true value of the result
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9 and its measurements taken by two boys are 3
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8
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8 is more accurate as it is closer to the true value
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85 is
more precise than 3
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Significant Figures
i
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There are certain rules for determining the number of
significant figures
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All digits are significant except zero in the beginning of a number
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iii
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For example, 0
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iv
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For example, 0
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v
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Thus, 2
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vi
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e
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000000 or 20 =
20
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Notes: In additions or subtractions, the final result should be reported to the same
number of decimal places as that of the term with the least number of decimal places
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These laws are known as
of chemical combination
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Law of conservation of mass: This law was put forth by Antoine Lavoisier in 1789
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ii
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This law states that a chemical compound is always found to be made of
same elements combined together in fixed proportion by weight
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iii
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According to
this law, When two elements combine to form two or more chemical compounds,
then weight of one of the element which combines with a fixed weight of the other,
bears a simple whole number ratio to one another
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For example, The ratio of masses of oxygen in CO and CO2 for fixed mass of

carbon (12) is 16 : 32 = 1 : 2
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Law of reciprocal proportions: It states that the ratio of weights of two elements A and
B, which combine separately with the fixed weight of a third element C is either
same or some simple whole number of the ratio of weights in which A and B
combine directly with each other
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v
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He observed that when gases combine or are produced in a chemical reaction they
do so in a simple ratio by volume, provided all gases are at the same temperature
and pressure
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vi
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Dalton's Atomic Theory
John Dalton in 1808 published “A New System of Chemical Philosophy” in which he
proposed atomic theory of matter
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Matter is made up of extremely small, indivisible particles called atoms
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Atoms of a given element are identical in all respect, i
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, they possess same size,
shape, mass, chemical properties etc
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Atoms of different elements are different in all respects, i
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, they possess different
sizes, shapes, masses, chemical properties etc
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Atoms of different elements may combine with each other in a fixed, simple, whole
number ratio to form compounds
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Atoms can neither be created nor destroyed in a chemical reaction
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Atomic Mass and Molecular Mass
a) Atomic Mass: Atomic mass can be defined as a mass of a single atom which is
measured in atomic mass unit (amu) or unified mass (u) where,
1 a
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u
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It is obtained by multiplying the atomic mass of each

element by the number of its atoms and adding them together
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Molecular mass of methane,
(CH4) = (12
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008 u) = 16
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00g of C-12
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022 × 1023

Chemical Formulae
Symbolic representation of compound is called chemical formula
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b) Molecular Formula: The molecular formula shows the exact number of different
types of atoms present in a molecule of a compound
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The various concentration terms are,
1
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2
...

3
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m = {Number of moles of solute/Mass of solvent (in kg)} × 100
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​ Molarity (M) – It is defined as number of moles of solute present in 1 L of
solution
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​ Mole fraction : Suppose, n is the moles of solute and N is the moles of solvent, then,
(i)
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Mole fraction of solvent (Xsolvent) =
୬ା

Xsolute + Xsolvent = 1
6
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N = Gram equivalent of solute
Volume of solution (litre) × 100

Limiting Reagent
Limiting reagent is the reactant which is completely consumed in a reaction
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N2(1 mole) + 3H2(3 mole) ⟶ 2NH3(2 mole)
It means 1 mole of N2 react with 3 mole of H2 to produce 2 mole of NH3
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Matter: Anything that occupies space and has mass
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Element: A pure substance which can neither be decomposed into nor built from
simpler substances by any physical or chemical method
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3
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It contains only one kind of molecules
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Mixture: A substance obtained by simple mixing of two or more pure substances
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Law of Conservation of Mass: During any physical or chemical change total mass of
the products formed is equal to the total mass of the reactants consumed
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Law of Constant Composition: A chemical compound always contains same elements
combined together in same proportion of mass
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Law of Multiple Proportions: When two elements combine with each other to form two
or more than two compounds then the masses of one of the elements that combine
with the fixed mass of the other, bear a simple whole number ratio to one another
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Gay Lussac's law: When gases react with each other they do so in volumes which
bear a simple whole number ratio to one another and to the volumes of products, if
there are also gases, provided all volumes are measured under similar conditions of
temperature and pressure
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Avogadro's Law: Equal volume of all gases under similar conditions contain equal
number of molecules
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Atom: The smallest particle of an element that takes part in chemical
reactions
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Molecule: The smallest particle of a substance that has
independent existence
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Atomicity: The number of atoms in a molecule of
the elementary substance
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Unified Mass (u): One-twelfth of the actual mass of an atom of carbon (C-12)
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66 × 10–27 kg
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Atomic Mass: The average relative mass of an atom of the element as compared
with mass of a carbon atom (C-12) taken as 12 u
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Molecular Mass: The average relative mass of a molecule of the substance as
compared with mass of an atom of carbon (C-12) taken as 12 u
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Gram Atomic Mass: The mass of 1 mole of atoms (6 × 1023) in g is called gram
atomic mass
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Gram Molecular Mass: The mass of 1 gram molecule of compound
expressed in grams
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Avogadro's Number (NA): 6
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19
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022 × 1023 specified particles
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Molar Mass: Mass of one mole particles of the substance
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Gram Molecular Volume (G
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V
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Its value is equal to 22
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T
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22
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Molecular
formula is whole number multiple of empirical formula
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Molarity (M): Number of moles of solute per litre of solution
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24
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25
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15
26
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Formula of Ferric Sulphate is:
(a) FeSo4
(b) Fe (So4)3
(c) Fe2 (So4)3

(d) Fe2So4
Question 2
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89
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9, the exact atomic weight of element would be
(a) 26
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9
(c) 17
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7
Question 3
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5H2O is (a) 27
(b) 21
(c) 5
(d) 8
Question 4
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The mass of the atom in a
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u
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2
(d) 12
Question 5
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4 g sample of ethyl alcohol contains 0
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The
amount of pure ethyl alcohol to the proper number of significant figures is
(a) 81
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40 g
(c) 91
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Which of the following halogen can be purified by sublimation?
(a) F2
(b) Cl2
(c) Br2
(d) I2
Question 7
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02 × 1023 atoms of H
(b) 4 g atom of Hydrogen
(c) 1

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