9/2/2008 – Class Notes
Chemistry – The Central Science
Pre-Scientific Method – Alchemists
Scientific Method – 1661, England Boyle
- Controlled Experiment
- Observation of Results
- Hypothesis
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Natural Law or Theory
A Theory explains the behavior of a phenomenon
A Natural Law doesn’t explain behavior, rather it states that there is a measurable relationship of some kind.
Measurements
There will never be 100% precise measurement.
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Measuring Volume: (Standard L or mL)
Graduated Cylinder
Beaker – fixed quantity, least accurate
Volumetric Flask – fixed quantity
Pipette – fixed quantity
Graduated Burette
Every measurement has a unit:
10 cal = energy/heat
10 sec = time – stop watch
10 kg = mass – balance, scale
10 cm = length – ruler
Every measurement has a degree of uncertainty ex. ±.001
Significant Digits
A significant digit is the digit that reflects the accuracy of the measurement.
Whole Numbers:
10,000 has 1 significant digit
10,005 has 5 significant digits
10,010 has 4 significant digits
Decimals – any zero preceding the decimal is non significant, any zero following the decimal after a non zero number is significant.
0.1 has 1 significant digit
0.100 has 3 significant digits
0.1000 has 4 significant digit
0.0002 has 1 significant digit
0.000200 has 3 significant digits
11.2420000 has 9 significant digits
Important
When solving a problem, both sides must have equal significant digits. Solve first, then round off to get the same number of significant digits in both the question and the answer.
Example:
Measure the Density mass/volume
1.2cm
v=1.2cm3
v=1.2*1.2*1.2
v=1.728cm
v=1.73 (rounded off so that the answer has the same amount of significant digits)
m=10.0052g
10.0052cm = 5.7833
1.73mL
The number with the least amount of significant digits is 1.73 and the answer will be converted into 3 significant digits
Density = 5.79
Scientific Notation
Represent very large or very small numbers in powers of 10
Any number raised to the power of zero is 1
For numbers 1 or higher, move the decimal to the left to determine the power
1=100
1=2000
10=101
100=102
1,000=103
10,000=104
1,000,000=106 or 1×106
1,200,000,000=1.2×109
For numbers less then 1, move the decimal to the right to determine the power
0.1 =10-1
0.01=10-2
0.001=10-3
0.0001=10-4
0.00001=10-5
25°c = Room Temp
