BASIC PRINCIPLES OF CHEMISTRY - gneet.com

[Pages:31]BASIC PRINCIPLES OF CHEMISTRY

Branches of chemistry

Organic chemistry : This branch deals with study of compounds of carbon and its compounds with any number of other elements, including hydrogen (most compounds contain at least one carbon?hydrogen bond), nitrogen, oxygen, halogens, phosphorus, silicon, and sulfur. Except carbonates, bicarbonates, cyanides, isocyanides, carbides and oxides

Inorganic chemistry: This branch deals with study of known elements and their compounds except organic compounds. It is concerned with materials obtained from minerals, air, sea and soil.

Physical chemistry: This branch deals with study of physical properties and constitution of matter, the laws of chemical combination and theories governing reactions. The effect of temperature, pressure, light, concentration on reaction.

Analytical chemistry: This branch deals with various methods of analysis of chemical substances both qualitative and quantitative.

Industrial chemistry : Chemistry involved in industrial process is studied in this branch.

Biochemistry : It comprise the studies of substances for the prevention and cure of various diseases in living beings

Nuclear chemistry : This branch deals with study of nuclear reaction, the production of radioactive isotopes and their application in various field.

Measurement in chemistry

A physical quantity is expressed in terms of pure number and unit Physical quantity = ( a pure number ) ? unit For example when we say 5 kg. It means 5 times of 1kg `A unit is defined as the standard of reference chosen in order to measure a definite physical quantity". Standard weight and measure are given by International system of Unit (SI)



Page 1

BASIC PRINCIPLES OF CHEMISTRY

Basic physical

Symbol of

Name of SI unit Symbol of SI

quantity

quantity

unit

Length

l

metre

m

Mass

m

kilogram

kg

Time

t

second

s

Electric current I

ampere

A

Thermodynamic T

kelvin

K

temperature

Amount of

n

mole

mol

substance

Luminous

Iv

Intensity

candela

Cd

Some time Sub-multiple and Multiples are used to reduce and

enlarge the size of different units

Sub ? multiples

Multiples

Prefix

Symbol Sub-

Prefix

Symbol Multiple

multiple

deci

d

10-1

deca

da

10

centi

c

10-2

hecto

h

102

milli

m

10-3

kilo

k

103

micro

10-6

mega

M

106

namo

n

10-9

giga

G

109

pico

p

10-12

tera

T

1012

femto

f

10-15

peta

P

1015

atto

a

10-18

exa

E

1018

Following convention is followed in writing a unit or its symbol

1. The symbols of the units are never expressed in plural form. For example, we write 15 cm and not 15 cms.

2. If a unit is named after the name of a person, it is not written with capital letter. For example, we write newton and not Newton

3. The symbol of the unit named after the name of a person is expressed in capital letter. For example, the symbol for unit newton is N and not n. Symbols of the other units are not written in capital letters. For example, symbol for unit meter is m and not M

4. Not more than one solidus is used. For example 1 poise is expressed as



Page 2

BASIC PRINCIPLES OF CHEMISTRY

1g/s cm or 1 g s-1 cm-1 and not 1g/s/cm.

Some derived units

a) Area = length ? breadth = m ? m = m2

b) Volume = length ? breadth ? height = m ? m? m =m3

c) Density = mass/ volume = kg/ m3 = kg m3

d) Speed = distance / time = m/s = m s-1

e) Acceleration = change in velocity / time = m s-1 /s = m s-2

f) Force = mass ? acceleration = kg m s-2

g) Pressure = force per unit area = kg m s-2 / m2 = kg m-1 s-2 or N m-2 ( pascal ? Pa)

h) Energy = force ? distance travelled = kg m s-2 ? m = kg m2 s-2 ( joule ? J)

Some conversions

a) Temperature Degree Centigrade = Kelvin ? 273.15

oC = K -273.15

= 9 ? ( ) + 32

5

b) Volume 1 litre (lit or L) = 1000 cm3 1 L = (10 cm)3 1 L = (10 ?10-2 m)3 1 L = 103 ? 10-6 m3 1 L = 10-3 m3 OR 1m3 = 1000 L Also



Page 3

BASIC PRINCIPLES OF CHEMISTRY

1 L = 1000 mL = 10-1 m3 = 1 dm3 c) Energy

1 cal = 4.184 J 1eV = 1.6 ?10-19 J d) Pressure 1 atm = 760 torr = 760 mmHg = 76 cmHg = 1.013?105 Pa

Significant figures To indicate the precision of measurement, scientists use the term significant figure. The following rules are observed in counting the number of significant figures in a given measured quantity. 1)All non-zero digits are significant : for example

24.3 has three significant figure 243.2 has four significant figure 2) A zero becomes significant figure if it appears between two nonzero digits: for example 3.04 has three significant figure 3.506 has four significant number 3) Leading zeros or the zero placed to the left of the numbers are never significant : For example 0.542 has three significant number 0.054 has two significant number 0.006 has one significant number 4) Trailing zero or the zeros placed to the right of the decimal are significant: For example 431.0 has four significant figures 432.00 has five significant number 5) If a number ends in zero but these zeros are not to the right of decimal point, these zeros may or may not be significant For example , 11400 g may have three, four or five significant figures. Such a number is first written in exponential form. The above mass may be written in the following exponential forms 1.14 ? 104 g which has three significant figures 1.140 ? 104 g has four significant figures 1.1400 ? 104 g has five significant figures 6) The non-significant figures in the measurements are round off a) If the figure following the last number to be retained is less than 5, all the unwanted figures are discarded and the last number is left unchanged e.g. 5,6724 is 5.67 to three significant figure



Page 4

BASIC PRINCIPLES OF CHEMISTRY

b) If the figure following the last number to be retained is greater than 5, the last figure to be retained is increased by 1 unit and the unwanted figures are discarded e.g 8.6526 is 8.653 to four significant figures c) If the figure following the last number to be retained is 5, the last figure is increased by 1 only in case it happened to be odd. In case of even number the last figure remains unchanged. For example 2.3524 is 2.4 to two significant figures ( 3 is odd hence increased by 1 ) 7.4511 is 7.4 to two significant figure ( 4 is even hence no increase) 7) Exact number have an infinite number of significant figures because infinite number of zero can be placed after decimal point Example 20 = 20.00000 .....

Calculations Involving Significant Figures

Rule 1 : The resultant of an addition or subtraction in the numbers having different precisions should be reported to the same number of decimal places as are present in the number having the least number of decimal places. The rule is illustrated by the following examples

a) 33.3 ( only one decimal place) 03.11 +00.313

Sum 36.723 ( Answer should be reported to one decimal place)

Correct answer 36.7

b) 3.1421 0.241 0.09 ( two decimal places)

Sum 3.4721 ( answer should be reported to 2 decimal place

Correct answer = 3.47

c) 62.831 - 24.5495

Difference = 38.2815 ( Answer should be reported to 3 decimal place after round off)

Correct answer = 38.282 ( as 1 is odd number hence increased by one )



Page 5

BASIC PRINCIPLES OF CHEMISTRY

Rule 2: The answer to a multiplication or division is rounded off to the same number of significant figures as is possessed by the least precise term used in the calculation. Example

a) 142.06

? 0.23 ( two significant figures)

32.6738 ( answer should have two significant figures, after rounding off)

Correct answer = 33

b) 51.028

? 1.31 ( three significant figures)

66.84668

Correct answer = 66.8

0.90 ) 4.26 = 0.2112676

Correct answer = 0.21

3.24 ? 0.0866 ) 5.046 = 0.055653

Correct answer = 0.0556

4.28 ? 0.146 ? 3

)

0.0418

= 44.84784

Correct answer = 44.8

Elements and compounds

Elements are pure substances that cannot decomposed into simpler substances by chemical change. The smallest particles of an element possess the same properties as the bigger particles. An element can also be defined as a pure substance which consists of only one type of atoms ( smallest particle)

Elements are classified in Metals, non-mental and metalloids



Page 6

BASIC PRINCIPLES OF CHEMISTRY

Compounds are also pure substances that are composed of two or more different elements in a fixed proportion by mass. The property of compound is altogether different than the constituent elements. For example water is made up of hydrogen which can burn and oxygen which helps to burn but Water extinguishes fire. Components of the compound cannot be separated by physical process but only by chemical process. If we just boil water Hydrogen and oxygen cannot be separated for that we have to go for electrolysis process

Compound are classified into two types:

i) Organic compounds : The compounds obtained from living sources are termed organic compounds. The term organic is now applied to hydrocarbons ( compounds of carbon and hydrogen) and their derivatives

ii) Inorganic compounds: The compounds obtained from nonliving sources such as rock and minerals are termed inorganic compounds. The compounds of all elements except hydrocarbons and their derivates are included in this category.

Some specific properties of substances:

i) Deliquescence: The property of certain compounds of taking up the moisture present in atmosphere and becomes wet when exposed is known as deliquescence. For example Sodium hydroxide, potassium hydroxide, calcium chloride, magnesium chloride anhydrous ferric chloride

ii) Hygroscopicity : Certain compounds combine with the moisture and are converted into hydroxides or hydrates. Such substances are called hygroscopic. Anhydrous copper sulphate, quick lime (CaO), anhydrous sodium carbonate etc are of hygroscopic nature

iii) Efflorescence: The property of some crystalline substances of losing their water of crystallization on exposure and becoming powdery on the surface is called efflorescence. Such salts are known as efflorescent. The examples are Ferrous sulphate (FeSO4 . 7H2O), sodium carbonate (



Page 7

BASIC PRINCIPLES OF CHEMISTRY

Na2CO3. 10H2O), Sodium sulphate ( Na2SO4 .10H2O) potash alum [ K2SO4 . Al2(SO4)3 . 24H2O] etc iv) Malleability : this property show by metals. When solid is beaten and does not break but converted into a thin sheet, it is said to posses the property of malleability. Example Gold , silver, copper v) Ductility : The property of metal to be drawn into wires is termed ductility. Example Gold , silver, copper. Platinum is most ductile. vi) Elasticity : When the stress ( force per unit area normal to cross-section) is small, the solid completely regain its original shape, size or volume after deforming force is removed. The solid is then said to be elastic. Steel, glass, ivory etc are elastic bodies vii) Plasticity : When stress is increased on a metal, a limit is reached beyond which, if the stress is removed, the solid does not come back to its original shape or size. It acquires a permanent deformation. Such material can be given any shape without any difficulty viii) Brittleness: The solid materials which break into small pieces on hammering are called brittle. The solids of nonmetals are generally brittle in nature ix) Hardness: A material is said to be harder than the other if it can scratch it. The hardness is measured on Mho's scale. For this purpose, ten minerals have been selected which have been assigned hardness from 1 to 10 On Mho's scale, hardness of diamond is maximum and that of talc is minimum.

Law of Chemical Combination

(i) Law of conservation of mass : The law was first stated by Lavoisier in 1774 .According to this law, in all chemical changes, the total mass of the system remains constant or in chemical change, mass is neither created nor destroyed. Total mass of reactant = Total pass of products + masses of the un-reacted reactants



Page 8

 ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download