Basic Chemistry :  Significant Figures

Significant Figures (Sig Figs) - The digits in a measurement that are reliable.  The certain digits and the one estimated digit of measurement.

Rules for Counting Significant Figures

  1. Digits 1-9 are always significant.
  2. Zeros within a number are always significant.
    e.g. 3209 has four sig figs.
  3. If there is a decimal point, zeros in front (to the left) of the non-zero digits are not significant.
    e.g.  0.00256 has three sig figs.
  4. If there is no decimal point, zeros at the end of the number are NOT significant.
    e.g. 74800 has three sig figs.
         74800. has five sig figs.
         748.00 also has five sig figs.
  5. The first part of a number written in scientific notation is always significant.
    e.g. 4.58 x 104 has three sig figs.

Rules for Significant Figures in Calculations

  • Addition/Subtraction
    • The accuracy of the final answer can be no greater than the least accurate measurement.
    • In other words, the answer can contain no more decimal places than the lest accurate measurement.
      e.g.  215.0 + 4.3985 = 219.4  with four sig figs.
      The first number only has accuracy to the tenths place, so the final answer can only be accurate to the tenths place no matter how accurate the other measurement is.

  • Multiplication/Division
    • The measurement can contain no more significant figures than the least accurate measurement.
    • In other words, the answer can contain only the same number of significant figures as the measurement with the smallest number of significant figures.
      e.g.  67.1009 x 4.22 = 283 with three sig figs
      The second number only has three sig figs, so the final answer can only have three sig figs no matter how many more sig figs the other measurement has.

Next:  "Nomenclature:  Common Elements"