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.

More facts about significant figures:

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

leading zeros aren’t counted though

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

Adding and Subtracting Significant Digits:

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

## No comments:

## Post a Comment