CH.2 THE CHEMIST’S TOOLBOX
Measurement
• Scientists must be curious and ask “why?”
• They must make observations on some aspect of nature, devise laws from those
observations and create a theory to give insight into reality
Tools needed for this procedure revolve around measurement
Expressing Uncertainty in Measured Quantities
• All measuring devices have limitations, therefore measurements always involve some
uncertainty
• Scientists report measured quantities in a way that reflects the precision associated with
the measuring device
• General rule for reporting measured quantities is:
Each digit in a reported quantity is taken to be certain, except for the last, which is
estimated
• When using measured quantities in calculations, must be careful to preserve the
certainty associated with the measure quantities
Scientific Notation
• A number written in scientific notation has 2 parts: a decimal part, a number between 1
&10; a and an exponential part, 10 raised to the exponent, n.
-10 exponent
• 1.2 X 10
Decimal part exponential part
• Meaning of n in the exponent:
Positive n = multiply by 10 n times
Negative n = divide by 10 n times
• Positive n:
10 = 1
10 = 1 X 10
10 = 1 X 10 X 10 = 100
10 = 1 X 10 X 10 X 10 = 1000
• Negative n:
10 = 1/10 = 0.1
-2
10 = 1/10 X 10 = 0.01 CH.2 THE CHEMIST’S TOOLBOX
-3
10 = 1/10 X 10 X 10 = 0.001
• To express a number in scientific notation:
1. Move the decimal point in the number to obtain a number between 1 and 10 (the
decimal part)
2. Write the decimal part multiplied by 10 raised to the number of places you moved the
decimal
3. The exponent is positive if you moved the decimal point to the left and negative if
you moved it to the right.
Units in Measurement
• Most measurements require a unit, a fixed agreed upon quantity by which other
quantities are measured
• When making measurements, we must be consistent in our use of units
• Numbers should always be written with their corresponding units, and units guide our
way through calculations
Important SI Standard Units
Quantity Unit Symbol
Length Meter m
Mass Kilogram kg
Time Second s
Temperature Kelvin K
SI Prefix Multipliers
Prefix Symbo Multiplier
l
Giga G 1,009,000,000
(10 )
Mega M 1,000,000
(10 )
Kilo k 1,000
(10 )
Deci d 0.1
(10 )1
Centi c 0.01 CH.2 THE CHEMIST’S TOOLBOX
-2
(10 )
Mili m 0.00-3
(10 )
Micro µ 0.000001
(10 )6
Nano n 0.0000000001
(10 )9
• The mass of an object is a measure of the quantity of matter within it
• The volume of an object is a measure of the amount of space it occupies

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