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Introduction
to fundamental concepts of chemistry


Define the following terms:  
Chemistry

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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 interrelations of
elements and compound. 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. 

Significant
Figures


Significant
figures are the reliable digits in a number or measurement
which are known with certainty. 

Significant figures show the accuracy in measurements. We can understand the precision of a measurement if we know exactly the significant figures in the measurement.  
A
measurement that contains more number of significant figures is more accurate
than a measurement that contains less number of Significant
figures. For example:Radius of a bob is 3.3679 cm and that of the other is 3.36 cm. In this situation the first measurement is the most accurate as it has more number of significant figures. 

Rules
Of Significant Figures

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In order to determine significant figures in a number we must follow the following rules:  
(1)
All the
nonzero digits are significant figures. For Example: 3.456 has four significant figures. 12.3456 has six significant figures. 0.34 has two significant figures. (2) Zeros between nonzero digits are significant. For Example: 2306 has four significant figures. 20,0894 has six significant figures. (3) Zeros locating the position of decimal in numbers of magnitude less than one are not significant. For Example: 0.2224 has only one significant figures. 0.0000034 has two significant figures. (4) Final zeros to the right of the decimal point are significant. For Example: 3.0000 has five significant figures. 1002.00 has six significant figures. (5) Zeros that locate decimal point in numbers greater than one are not significant. For Example: 30000 has only one significant figure. 120000 has two significant figures. 

Rules
Of Rounding Off Data

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Rule
# 1: If the digit to be dropped is greater than 5, then add "1" to the last digit to be retained and drop all digits farther to the right. For example: 3.677 is rounded off to 3.68 if we need three significant figures in measurement. 3.677 is rounded off to 3.7 if we need two significant figures in measurement. 

Rule
# 2: If the digit to be dropped is less than 5, then simply drop it without adding any number to the last digit. For example: 6.632 is rounded off to 6.63 if we need three significant figures in measurement. 6.632 is rounded off to 6.6 if we need two significant figures in measurement. Rule # 3: If the digit to be dropped is exactly 5 then: (A) If the digit to be retained is even, then just drop the "5". For example: 6.65 is rounded off to 6.6 if we need two significant figures in measurement. 3.4665 is rounded off to 6.466 if we need four significant figures in measurement. (B) If the digit to be retained is odd, then add "1" to it. For example: 6.35 is rounded off to 6.4 if we need two significant figures in measurement. 3.4675 is rounded off to 6.468 if we need four significant figures in measurement. Remember: Zero is an even number 3.05 is rounded off to 3.0 if we need two significant figures in measurement. 

Use
of significant figures in
addition and subtraction 
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In
addition and subtraction we consider the significant figures on the right
side of decimal point. This means that only as many digits are to be retained to the right side of decimal point as the number with fewest digits to the right of the decimal point. For example: 4.345 + 23.5 =27.845 (actual answer by using calculator) Answer after rounding off: 27.8 

Use
of significant figures in
multiplication and division 

In
multiplication and division , the number obtained after calculation of two
or more numbers must have no more significant figure than that number used in multiplication or division. For example: 4.3458 x 2.7 =11.73366(actual answer by using calculator) Answer after rounding off: 12(because 2.7 has only two significant figures) 
