Concept of Chemistry[Class=11]Part=3

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• Significant figures
  • The uncertainty in the experimental or the calculated values is indicated by mentioning the number of significant figures.
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  • Significant figures are meaningful digits which are known with certainty.
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  • There are certain rules for determining the number of significant figures. They are as follows:
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  1. All non-zero digits are significant.
  • For example: - There are 4 significant figures in 328.2 cm.
  2. Zeros preceding to first non-zero digit are not significant.
  • For example: - 0.03 has one significant figure and 0.0052 has two significant figures.
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  3. Zeros between two non-zero digits are significant.
  • For example: - 2.005 have 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: - 200 g has three significant figures. But, if otherwise, the zeros are not significant. For example, 100 have only one significant figure.
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  5. Exact numbers have an infinite number of significant figures.
  • For example:- In 2 balls or 20 eggs, there are 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.
  
  
  Addition & Subtraction
  • The result cannot have more digits to the right of the decimal point than either of the original numbers.
    • For example: - (12.11 + 18.0+ 1.012) = 31.122. As 18.0 have only one digit after the decimal point therefore the result will be 31.1, one digit after the decimal point.
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  Multiplication & Division
  • In these operations, the result must be reported with no more significant figures as are there in the measurement with the few significant figures.
    • For example: - 2.5×1.25 = 3.125. Answer will be 3.1 because 2.5 have two significant figures and the result should not have more than two significant figures.
  Problem:-
  How many significant figures are present in the following?
  (i) 0.0025
  (ii) 208
  (iii) 5005
  (iv) 126,000
  (v) 500.0
  (vi) 2.0034
  Answer:-
  (i) 0.0025
  There are 2 significant figures.
  (ii) 208
  There are 3 significant figures.
  (iii) 5005
  There are 4 significant figures.
  (iv) 126,000
  There are 3 significant figures.
  (v) 500.0
  There are 4 significant figures.
  (vi) 2.0034
  There are 5 significant figures.
  Problem:-
  Round up the following upto three significant figures:
  (i) 34.216
  (ii) 10.4107
  (iii) 0.04597
  (iv) 2808
  Answer:-
  (i) 34.2
  (ii) 10.4
  (iii) 0.0460
  (iv) 2810
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