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Chemistry UNIT 1
Susie SmithAugust, 2010
Chemistry is the study of matter.
Scientific Method
A logical method of problem solving.
Steps of the Scientific Method
Making observations that lead to a question. Forming a hypothesis to answer the
question. Testing the hypothesis by experimentation. Making a conclusion based on the results.
Definitions
Observation- use of senses and devices in the lab to obtain information.
Conclusion- a statement based on observations and prior knowledge.
Types of observations
Quantitative- includes numbers and units. Qualitative- does not include numbers and
units. Examples-
Hypothesis- an educated guess
Explains an observation. Can be tested. Will predict an outcome. Must be written as a statement.
Experiment
Designed to test an hypothesis. Involves variables Is performed under controlled conditions.
Variables
Variables are factors that can be changed.– Control variable is a variable that is held constant.– Manipulated or independent variable is changed
by the scientist.– Responding or dependent variable changes as a
result of the experiment.
International System (SI)
Measuring system used in science (also called the MKS)
Length
Distance between two points Base Unit- Meter (m) Instrument- meter stick or metric ruler
Mass
Amount of matter in a substance Base Unit- gram SI Unit – kilogram Instrument- triple-beam balance
Volume
Amount of space an object occupies Base Unit- liter (L) Instrument- metric ruler or graduated cylinder
Time
Interval between two occurances Base Unit- second (s) Instrument- stop watch
Temperature
Average kinetic energy Base Unit- Celsius (oC) or Kelvin (K) Instrument- thermometer.
Scientific Notation
Numbers are expressed in this form: M X 10n
M is a number between 1 and less than 10.
And n is equal to an exponent.
How to take numbers out of scientific notation
1 X 103 = 1000 Positive exponents move the decimal
place to the right n spaces. 1 X 10-3 = .001 Negative exponents move the decimal
place to the left n spaces.
Scientific Notation
6.2 X 104
1.5 X 10-2
2.4 X 10-5
7.06 X 106
6.0 X 106
How to put numbers into Scientific Notation
6,011,000 0.058 24 0.009009 6.734114
Conversion Factors
One large unit = how many smaller units. One dozen = 12 units.
Common Conversions
“Prefix Abbreviation Conversion fact
Mega M 1Mm = 1,000,000 m
Kilo k 1km = 1,000 m
Deci d 1m= 10dm
Centi c 1m= 100cm
Milli m 1m= 1,000 mm
Micro 1m= 1,000,000 m
Conversions
Start every problem with the original amount.
Then use a conversion fact to convert the units of measurement to what you need.
Set up every problem as a fraction with the unit you are looking for on top and the unit you started with on bottom.
Practice Problems
1 kg = ________ g 1s = _________ ds ________ = 1 L ______ dollars = 100 centidollars 100 dg = _____ g
How to work your calculator?
Look for EE, X10, or ^ keys on your calculator
Every calculator is different. Make notes about how to use your
calculator.
Practice
Convert 152 cm to m. Use the conversion fact 1m = 100cm 152 cm X 1m = 1.52 m
100 cm
Conversion Practice
Convert 62 kg to _________ g. Convert 1700 m to _______ m Convert 0.0056 mm to ______km.
Conversions with Derived Units
Convert 570 g/L= __________ g/mL 16 m/min = ______________ m/s Convert 65 km/h =____________ m/s
Order of operations
Please Excuse My Dear Aunt Sally. Parenthesis Exponents Multiply or Divide Addition or Subtraction
Definitions
Accuracy- closeness of a measurement to the accepted value
Precision- the reproducibility of a measurement
Significant Digits
All measured digits plus 1 estimated digit Read the smallest division on the instrument
and then estimate one more digit 3.21 cm, _____ significant digits, ____
measured and ___ is estimated.
Zeros and significant digits
Zeros are placeholders. They are only significant if they are in between
two non zero numbers. 906 They are significant if they follow a non zero
number and are after a decimal. 15.00 They are not significant if they are before a
decimal and before a non zero number. 0.0015 They are significant if a bar is placed on top of
the 0.
Rules for rounding
After multiplying or dividing– Round to the least number of significant digits– Round to the weakest link.– Ex. 420 X 100 = _________
Rounding
After adding and subtracting,– Round answer to 1st column containing an
estimated digit– Round to the weakest column
12.001
4.02
+ 3
19.021 19
Rule of 5’s
When a number is exactly half way between two numbers, always round to the even number.
12.5 rounds to 12 11.5 rounds to 12 12.5001 rounds to 13
Scientific Method
Variable- a physical quantity which can change in the experiment
In a good experiment, only one variable is allowed to change.
Parts of an Experiment
Manipulated (independent) variable- is changed by the experimentor
Responding (dependent) variable- depends on the results of the experiment
Control variables- are variables that are held constant on each group.
Weight verses Mass
On the moon, your mass would not change, and your weight would change.
Mass- is the amount of matter an object has– kilograms
Weight- is the affect of gravity pulling on an object– Newtons
Scientific Method
Question Hypothesis Research Experimentation Conclusion Retest
Graphing scientific data
X axis- independent variable Y axis- dependent variable means “is directly proportional to”
Straight Line Graph y x
y = kx , where k is a constant Slope is y/x or rise/run
Inverse proportion y 1/x
y = k/x Graph is a hyperbola
Equations
When the variables of an equation are on the same side of the equal sign, the variables are inversely proportional.
When the variables of an equation are on opposite sides of the equal sign, the variables are directly proportional.
P A = F
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