chemical foundations chapter 1. the scientific method observation hypothesis experiment theory...
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The Scientific MethodObservation
Hypothesis
Experiment
Theory (model)
Prediction
Experiment
TheoryModified
As needed
Law
Summary of observed
(measurable) behavior
Ex: law of conservation of
mass
A Theory (model) attempts to explain
why it happens
The Scientific MethodQualitative Quantitative
Overview:• Deals with descriptions• Data can be observed but not measured• Colors, textures, smells etc.•Qualitative -----Quality
Overview:• Deals with numbers• Data which can be measured• Length, Height, volume, weight, speed, time, temp• Quantitative-----Quantity
Example: Oil Painting• Blue & green paint• Gold frame• Masterful brush strokes
Example: Oil Painting• 10” x 14”• surface area 140 in2
• Weight: 8.5 pounds
Units of Measurement (1.3)
Physical Quantity Name of Unit Abbreviation
Mass Kilogram kg
Length Meter m
Time Second s
Temperature Kelvin k
Electric Current Ampere A
Amount of substance Mole mol
Luminous intensity Candela cd
SI System: based on the metric system and units derived from the metric system.
Units of Measurement (1.3)
Symbol Prefix Factor
G giga 109
M mega 106
k kilo 103
h hecto 102
da deka 101
BASE
d deci 10-1
c centi 10-2
m milli 10-3
μ micro 10-6
n nano 10-9
Units of Measurement (1.3)
Volume: is not a fundamental SI unit but is extremely important in chemistry. Volume can be derived from length.
Units of Measurement (1.3)
Mass vs. Weight
Remember MASS IS NOT THE SAME AS WEIGHT!
Mass is a measure of the resistance of an object to a change in its motion.
Weight is the response of mass to the force of gravity.
Uncertainty in Measurement (1.4)
Uncertainty: the uncertainty of measurement depends on the precision of the measuring device.Report any observed measurements by recording all the certain digits plus the first uncertain digit.
20.15 ml20.1 is certain 0.05 is uncertain
Precision and Accuracy (1.4)
Accuracy: agreement of a particular value with the accepted value.Precision: agreement among several measurements of the same quantity (reproducibility).
Precision and Accuracy (1.4)
Random Error: equal probability of being high or low.Systematic Error: error that occurs in the same direction each time.
Significant Figures & Calculations (1.5)
Scientific Notation
98,500,000 = ? 9.85 x 107
64,100,000,000 = ? 6.41 x 1010
0.0000000279 = ? 2.79 x 10-8
4,200,000 = ? 4.2 x 106
Significant Figures & Calculations (1.5)
Rules for counting Significant Figures:
1. Nonzero integers always count!2. Zeroes (3 classes):
a. Leading zeroes do not count (place holders)b. Captive zeroes do count
c. Trailing zeroes are if there is a decimal point
3. Exact numbers (counting or from definitions)
Significant Figures & Calculations (1.5)
Rules for Significant Figures in calculations:
1. For multiplication or division: the resultant is the same as the LEAST precise number in the calculation.2. For addition or subtraction: the resultant is the same number of decimal places as the least precise measurement in the calculation.
3. Rounding: DO NOT round until all calculations are completed. Use only the first number to the right of the last significant figure.
Dimensional Analysis (1.6)
Unit Factor Method/Dimensional Analysis: converting a given result from one system of units to another.
• Start with what value is known, proceed to the unknown.
• Draw the dimensional lines.• Insert the unit relationships.• Cancel the units.• Do the math, include units in answer.
Rules for Dimensional Analysis:
Notice that 1 kelvin = 1 degree Celsius
Boiling point of water
Freezing point of water
Celsius
100 ˚C
0 ˚C
100˚C
Kelvin
373 K
273 K
100 K
Fahrenheit
32 ˚F
212 ˚F
180˚F
Temperature (1.7)
Density (1.7)
Recall that you can measure either the volume or the mass of an object. Density is a property that describes the relationship between these two measurements.
Density (1.7)
Compound Density in g/cm3 at 20o C
Chloroform 1.492
Diethyl ether 0.714
Ethanol 0.789
Isopropyl alcohol 0.785
Toluene 0.867
A chemist has an unknown solution that he wants to identify. He measured out exactly 25.00 ml (cm3) of the substance and found that it has a mass of 19.735 g at 20 C.
Density = 19.735 g/25.00 cm3 = 0.794 g/cm3
Classifying Matter
A homogeneous mixture is the same throughout with visibly indistinguishable parts. (Solutions)
A heterogeneous mixture is one that has visibly distinguishable parts.
Mixtures (a variable composition)
Substances, on the other hand, cannot be separated into different kinds of matterby physical means such as sorting, filtering, heating, or cooling. (ex: Table salt)
Classifying Matter
Some substances, like silver, contain only one kind of matter. These substances are called elements.