## Tuesday, October 26, 2010

### Significant Figures - Isabelle Cheng

Isabelle Cheng
October 26,2010
Block 2-2 Chemistry 11
Ms. Chen
Significant Figures
Significant figures are the number of significant digits in an answer to a calculation. They are approximate answers and the more digits it has the more accurate it may be.
non- zero numbers are significant - for example: 355 has three significant digits, and 24.35 has four digits
however with zeros there are different rules:
zeros put between other digits are always significant
zeros put after another digit but behind a decimal are significant
zeros put before other digits are not significant
zeros at the end of a number are significant only when they are after the decimal point
Exact numbers - Ex. there are exactly 14 dogs. You can’t have 14.34 dogs.
Inexact numbers - Ex. the length of the table is 124.34 mm then it is an inexact number.
Rounding numbers - round answers to the approximate - Example: if the number is over 5 then round it to a high number and if it is under five keep it that number. If the number equals to five the put a five
round up to the fewest numbers of the decimal places
ex. 14.982+4.2 would be looking like 14.982 = 19.182
+   4. 2
same thing for subtracting!
round to the thousands place for the first uncertain digit
ex. 24500+7000 = 31,900 - you have to change it to 34,500 = 34,000
Multiplying and Dividing Significant Digits:
round to the nearest number significant digits
ex. 32.96 x 2.4 = 79.104 - multiplying
ex. 14.59 ÷ 5 = 2.918 - dividing
Some exercises of significant figures:
Write how many significant figures there are!
195.21
0.0001000
949932
1.00 x 1000000
5003.0
0.000938
1009
15310.4
350092849
0.0021780