1. Scientific Measurements
Chemistry I
Mr. Skeen
Ch. 3

2. How Reliable are Measurements
Accuracy
How close a measured value is to an accepted value
Precision
How close a series of measurements are to one another

3. Percent Error Significant Figures
Ratio of an error to an accepted value
% error = error/accepted value X 100
Error = accepted value – measured value
Significant Figures
All known digits plus one estimated digit

4. Rules for recognizing significant figures (sig. fig.)
Non-zero numbers are always significant
Zeros between significant numbers are always significant
All final zeros to the right of the decimal are significant
Zeros that act as place holders are not significant
Convert to scientific notation
Counting #s and defined constants have an infinite # of significant figures

5. Rules for Rounding
If the digit to the immediate right of the sig. fig. is
< 5 don’t change the last sig. fig.
> 5 round the last sig. fig. up
= 5 and followed by a nonzero digit round the last sig. fig. up
= 5 and not followed by a nonzero digit, look at the last sig. fig. If it’s odd round up, if it’s even do not change the last sig. fig.

6. Applying Rounding Rules
Addition and Subtraction
Answer must have the same # of sig. fig. to the right of the decimal as the value with the fewest digits to the right of the decimal
Multiplication and Division
Answer must have the same # of sig. fig. as the measurement with the fewest sig. fig.

7. Units of Measurement SI Units Base Unit Derived unit
Systeme International d’Unites
1960 International Committee
Base Unit
Based on an object or event in the physical world
Derived unit
A unit defined by a combination of SI base units

8. Quantity
Base Unit
Abbreviation
Time
second s
Length
meter m
Mass
kilogram kg
Temperature
kelvin K
Amt. of a Substance
mole
mol
Electric current
ampere A
Luminous Intensity
candela cd

9. Prefix
Symbol
Factor
giga- G
109
mega- M
106
kilo- k
103
deci- d
1/10, 10-1
centi- c
1/100, 10-2
milli- m
1/1000, 10-3
micro
10-6
nano- n
10-9
pico- p
10-12

10. Dimensional Analysis Conversion Factor Dimensional Analysis
Ratio of equivalent values used to express the same quantity in different units
Dimensional Analysis
Method of problem-solving that focuses on units

11. Density
Ratio comparing the mass of an object to the volume of that same object.
Relationship with temperature and pressure