Units and Measurement: Chemistry Mrs. Coyle
Units and Measurement: Chemistry Mrs. Coyle
Units and Measurement: Chemistry Mrs. Coyle
the language of Science SI Units International System MKS Meter m Mass kg Time s National Bureau of Standards Prefixes
SI Unit Prefixes
Name gigamegakilodecicentimillimicronanopicoSymbol G M k d c m n p 109 106 103 10-1 10-2 10-3 10-6 10-9 10-12
Scientific Notation
Mx
M
n 10
Other Examples:
5.45E+6
5.45 x 10^6
Limits of Measurement
Accuracy
and Precision
Accuracy
- a measure of how close a measurement is to the true value of the quantity being measured.
Example: Accuracy
Who
is more accurate when measuring a book that has a true length of 17.0cm? Susan: 17.0cm, 16.0cm, 18.0cm, 15.0cm
Precision
a measure of how close a series of measurements are to one another. A measure of how exact a measurement is.
Example: Precision
Who is more precise when measuring the same 17.0cm book?
Accurate
Error
Error= experimental accepted value
Percent Error
% Error= |experimental accepted| x100 accepted value
B) Significant Figures
Significant Figures
The
significant figures in a measurement include all of the digits that are known, plus one last digit that is estimated.
Sig Figs
answer has the same sig figs as the factor with the least sig figs. Ex: 3.22 cm x 2.0 cm 6.4 cm2
Counting Numbers
Counting
figs.
Ex:
3 apples
Quantity
Unit
Length
Mass Temperature Time
meter
kilogram kelvin second
m
kg K s mol cd a
Density Speed
Newton Energy Pressure
dm3
L mL Liter
1cm3= 1mL
Temperature
A measure of how hot or how cold an object is.
SI Unit: the kelvin
Note:
(K)
Temperature Scales
oF=
(1.8 oC ) +32
J 1 cal= 4.184 J
calorie
Note:
1 Cal = 1kcal =1000cal
SI Unit Prefixes
Name gigamegakilodecicentimillimicronanopicoSymbol G M k d c m n p 109 106 103 10-1 10-2 10-3 10-6 10-9 10-12
Factor-Label Method
Example:
Convert 5km to m:
Convert 7,000m to km
7,000m x 1 km = 7 km 1,000m
Convert 2.45cs to s
2.45cs
x 1s = 0.0245s 100cs