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General Chemistry
Fall ‘09
People often confuse Controls & Variables in experiments
A control is… A trial that duplicates all conditions except the
variable being investigated A variable is…
Either dependent (responding)- this is observed during the experiment
Or independent (manipulated)- what you (I) change during an experiment
People often confuse Observations &
Hypotheses An observation…
Is information collected with the senses
A hypothesis… A proposed explanation
for an observation.
Ivan Pavlov observed dogs salivating and
hypothesized that a sound would cause
dogs to salivate.
Identify the following as an observation or a hypothesis 1. Wearing tennis shoes will make one run faster.
2. The tennis shoes are black and red.
3. The Bunsen Burner flame is 1400°C and is blue.
4. People who take good notes will do better on tests.
Hypothesis
Observation
Observation
Hypothesis
Scientists make observations all the time. There’s two types:
Qualitative Quantitative
To remember the difference, look at their root
Qualities of the reaction, object, etc. Examples
The copper (II) sulfate is blue The nail is rusty Gas was given off
http://upload.wikimedia.org/wikipedia/commons/d/d8/Copper_sulfate.jpg
http://www.learner.org/channel/courses/essential/physicalsci/images/s4.rusty_nail.jpg
Quantity= numbers Mass, a number of paper clips, volume
measurements, molar measurements. Math is usually involved
Theory A well-tested explanation for a broad set of
observations Can help predict the behavior of matter and form
mental images Can be modified if new observations are made
Scientific Law A concise statement that summarizes the results of
many observations and experiments. Do not describe relationships, that requires a theory Ex) Charles’ Law
Scientific notation A number is written as the product of two numbers
A coefficient 10 raised to a power
Example: 602,000,000,000,000,000,000,000 Written as 6.02x1023
Coefficient is equal to or greater than 1 and smaller than 10
Try these:
1. 200,000,000,000 = ___________________
2. 0.00073 = ____________________
3. 1430 = __________________
If exponent is negative, which way does decimal go? If exponent is positive, which way does decimal go?
“Correctness” and “reproducibility” Accuracy
A measure of how close a measurement comes to the actual or true value of whatever is measured
Precision A measure of how close a series of measurements
are to one another
Measurements may be accurate or inaccurate Accepted value- correct value, based on
reliable resources Experimental value- value measured in the lab The difference between the two is called error
The absolute value of the error divided by the accepted value, multiplied by 100%
Example: boiling point was measured to be 99.1oC, but we know it’s 100oC
%error = 99.1oC – 100oC x100% 100oC
%error = 0.9%
Metric system is much easier than the English system…the conversion is always a factor of 10.
SI Base Units
Quantity SI Base Unit Symbol
Length meter m
Mass kilogram kg
Temperature kelvin K
Time second s
Amount mole mol
Length is a 1-dimensional measure of distance. Metric system base unit is the meter,
abbreviated m
Commonly Used Metric Prefixes
Prefix Meaning Factor
Mega (M) 1 million x larger 106
Kilo (k) 1000x larger 103
Deci (d) 10x smaller 10-1
Centi (c) 100x smaller 10-2
Milli (m) 1000x smaller 10-3
Micro 1 million x smaller 10-6
Nano (n) 1000 x smaller 10-9
Pico (p) 1 trillion x smaller 10-12
Volume is a measure of the amount of space a substance takes up. Metric system base unit is the liter,
abbreviated L.
Mass is a measure of the amount of matter in a substance. Metric system base unit is the
kilogram, abbreviated kg
• Response of mass to the pull of gravity
• Weight changes when on different planets
• NOT THE SAME AS MASS!
A measure of how hot or cold an object is.
Heat moves from hot to cold Celsius scale
Freezing point = Boiling point =
Kelvin scale Freezing point = 273 kelvins (K) Boiling point = 373 K Absolute zero = 0K (zero kinetic
energy)
Kilo hecto deka (m, g, L) deci centi milli k h dk or D d c m
How do you remember the order of the prefixes?
kilo
1000 hecto
100 deka
10 Base
Unit deci
1/10 centi
1/100 milli
1/1000
To convert to a larger unit, move the decimal point to the left or divide:
To convert to a smaller unit, move the decimal point to the right or multiply:
kilo
1000 hecto
100 deka
10 Base
Unit deci
1/10 centi
1/100 milli
1/1000
Convert 6 cm = _____ mm
We are converting to:
a) larger unit
b) smaller unit
Convert 6 cm = 60 mm
kilo
1000 hecto
100 deka
10 Base
Unit deci
1/10 centi
1/100 milli
1/1000
Convert 40 mm = _____ cm
We are converting to:
a) larger unit
b) smaller unit
Convert 40 mm = 4 cm
kilo
1000 hecto
100 deka
10 Base
Unit deci
1/10 centi
1/100 milli
1/1000
Convert 90 cm = _____ m
We are converting to:
a) larger unit
b) smaller unit
Convert 90 cm = 0.9 m
kilo
1000 hecto
100 deka
10 Base
Unit deci
1/10 centi
1/100 milli
1/1000
Convert 200 mm = _____ m
We are converting to:
a) larger unit
b) smaller unit
Convert 200 mm = 0.2 m
Make the following metric conversions 1. 875 cm = _________ m
2. 1.24 km = _________ m
3. 90,344 m = _________ km
4. 0.95 km = _________cm
8.75
1,240
875 / 100
1.24 x 1000
There is always an error in a measurement
The human eye can read one decimal place beyond the accuracy of the instrument
The measurement should be read
as 8.0 +/-0.1cm.
65
60
55
10
9
8
150
100
50
Container #1 Container #2 Container #39.02 mL 82 mL 62.0 mL
Read the volumes of the liquids below