Transcript Significant Figures…

Regents Chemistry
• Significant Figures
Five-minute Problem
• How many significant figures are in the
following: (write the number and answer)
125
1.256
0.0000004567
0.00300
1.004623
Significant Figures…Why?
• Allow us to make an accurate
measurement!
• Contain certain numbers
and one uncertain number
Certain Numbers
• Same regardless of who made the
measurement
• Actual divisions marked on
instrument
• Example: Ruler, beaker
Uncertain Numbers
• Are an estimate
• Vary by person and trial
• For example: estimate with a ruler,
beaker
Significant Figures Include...
• All certain numbers and one uncertain
number
• For example: 8.55 cm is actually
8.55 +- 0.01
The last digit is not actually on the ruler
you must make an estimate!
Rules for Counting Sig. Figs.
• 1. Nonzero integers - always count
– ex: 1322 has four significant figures
• 2. Zeros
– Leading Zeros - precede all nonzero digits
and do not count! Ex: 0.00025
– Captive Zeros - fall between nonzero digits
and always count! Ex: 1.008
– Trailing Zeros - zeros at end of number Ex. 100. vs. 100
Significant only if the number contains a decimal
Rules for Counting Sig. Figs.
• 3. Exact Numbers - have an unlimited
amount of significant figures…
• 2 Kinds
Describe something…50 cars, 25 bugs
By definition… 1 in = 2.54 cm
Rounding Numbers and Sig Figs
• Less than 5
• Equal to/more than 5
Sig Figs in Calculations
• Multiplication and Division
Smallest amount of significant figures determines..
Ex: 4.56 x 1.4 = 6.384
(3)
Round off
6.4
(2)
(4)
Ex: 8.315
298
(3)
=
0.0279027 Round off
2.79 x 10-2
Sig Figs in Calculations
• Addition/Subtraction - the number with the
smallest amount of decimal places limits
amount of significant figures
Ex: 10.2 + 1.7 + 4.13 + 5.765
= 21.795
21.8
Round off
Ex: 25 + 15.2 + 125.5 = 165.7
Round off
166