chemistry, the scientific method, and the si system of units
TRANSCRIPT
Chemistry, the Scientific Method, and the
SI System of Units
Chemistry is the study of matter
and the transformations it can undergo…
Chemistry is the study of matter
and the transformations it can undergo…
Chemistry Is All Around Us
…Matter is anything that occupies space.…Matter is anything that occupies space.
Parts of the Scientific Method
• Identify an unknown.• Make a hypothesis
(a testable prediction).• Experiment to test
the hypothesis.• Draw a valid conclusion.
Using the scientific method requires that one be a good observer.
observation inference
involves a judgmentor assumption
uses the fivesenses
DataObservations are also called data.
There are two types of data.
qualitative data quantitative data
descriptions; measurements; no numbers must have numbers
and UNITS
A Scientific Experiment
procedure
the order of events
in an experiment;
the “recipe”
Experiments must be controlled; they
must have two set-ups that must differ
by only one variable.
The conclusion must be based on the data.
variable
any factor that
could influence
the result
Make observationMake observation
Ask questionAsk question
Develophypothesis
Develophypothesis
Test hypothesis with an
experiment
Test hypothesis with an
experiment
Analyze dataand draw
conclusions
Analyze dataand draw
conclusions
Hypothesis IS
supported
Hypothesis IS
supported
Hypothesis is NOT
supported
Hypothesis is NOT
supported
Developtheory
Developtheory
Test hypothesis with furtherexperiments
Test hypothesis with furtherexperiments
Revisehypothesis
Revisehypothesis
Scientific Method
A Common System for Trade
In 1790, the French government appointed a committee of scientists to develop a universal measuring system.
English system of measurement originated in 1215 with the signing of the Magna Carta. It attempted to bring uniform measurements to world trade.
It took ~10 years, and they unveiled the Metric system.
length meter mmass gram gvolume liter Ltime second s
The SI International System of Units
Length meter m
Mass kilogram kg
Time second s
Amount of substance mole mol
Thermodynamic temperatureKelvin K
Electric current amperes amps
Luminous intensity candela cd
Quantity Name Symbol
Using only these 7 units, all other units of measurement can be derived. For example, area is meters squared. Another example
is electric charge which is amps multiplied by seconds.
Derived Units Commonly Used in Chemistry
Area square meter m2
Volume cubic meter m3
Force newton N
Pressure pascal Pa
Energy joule J
Power watt W
Voltage volt V
Frequency hertz Hz
Electric charge coulomb C
Quantity Name Symbol
Prefixes in the SI System
Power of 10 for Prefix Symbol Meaning Scientific Notation_______________________________________________________________________
mega- M 1,000,000 106
kilo- k 1,000 103
deci- d 0.1 10-1
centi- c 0.01 10-2
milli- m 0.001 10-3
micro- m 0.000001 10-6
nano- n 0.000000001 10-9
The Commonly Used Prefixes in the SI System
Area and Volume: Derived Units
Area = length x width
= 5.0 m x 3.0 m
= 15 ( m x m)
= 15 m2
Volume = length x width x height
= 5.0 m x 3.0 m x 4.0 m
= 60 ( m x m x m)
= 60 m3
Significant Figures, Precision, and Accuracy
Significant Figures• Significant figures are numbers that
mean something when reporting a value.
• Just because your calculator gives out the value 0.5384615 when 7.00 is divided by 13.0, to a scientist not all of the numbers in 0.5384615 have meaning.
• Significant figures reflect the significance of the measurements upon which the scientific calculation is based.
Rules for Counting Significant Figures -
DetailsNonzero integers always count as significant figures.
3456 has 4 sig figs.
Rules for Counting Significant Figures -
DetailsZeros
Leading zeros do not count as
significant figures.
0.0486 has 3 sig figs.
Rules for CountingSignificant Figures -
Details
Zeros Captive zeros
always count as significant figures.
16.07 has 4 sig figs.
Rules for CountingSignificant Figures -
DetailsZeros Trailing zeros are significant only if the number contains a decimal point.
9.300 has 4 sig figs.
Rules for CountingSignificant Figures -
Details
• Exact numbers (such as those in conversion factors) have an infinite number of significant figures.
1 inch = 2.54 cm, exactly
Sig Fig Practice #1How many significant figures in each of the following?
1.0070 m
17.10 kg
100,890 L
3.29 x 103 s
0.0054 cm
3,200,000
Use the Rounding Poem to Round Numbers CorrectlyFind your numberLook right next door4 or less, just ignore5 or greater add one more!
Round 4.167 to the closest hundredths4.167 Find your
numberLook right next door4.17
Rules for Significant Figures in Mathematical
Operations
Multiplication and Division: the # of sig. figs. in the result equals the number in the least precise measurement (lowest # of sig. figs.) used in the calculation.
6.38 x 2.0 = 12.76 13 (2 sig figs)
Sig Fig Practice #2
3.24 m x 7.0 m
Calculation Calculator says: Answer:
22.68 m2 m2
100.0 g ÷ 23.7 cm3 4.219409283 g/cm3 g/cm3
0.02 cm x 2.371 cm 0.04742 cm2 cm2
710 m ÷ 3.0 s 236.6666667 m/s m/s
1818.2 lb x 3.23 ft 5872.786 lb·ft lb·ft
1.030 g ÷ 2.87 mL 2.9561 g/mL g/mL
Precision and AccuracyAccuracy refers to the agreement of a particular value with the true value. If the true value were 5.00 and three measured values 2.0, 6.0, and 7.0 average out to 5.0 (as they do), then that set of measurements would be accurate.
Precision refers to the degree of agreement among several measurements made in the same manner.
Neither accurate nor
precise
Precise but not accurate
Precise AND accurate
Reporting Measurements
• This is where significant figures come from: actual measurements obtained in the laboratory.
• Report what is known with certainty
• Add ONE digit of uncertainty (estimate it!)
Practice Measuring
cm0 1 2 3 4 5
cm0 1 2 3 4 5
cm0 1 2 3 4 5
Avoid Parallax Errors When Measuring
Parallax errors arise when a meniscus or needle is viewed from an angle rather than from straight-on at eye level.
Correct: Viewing the meniscus
at eye level
Incorrect: viewing the meniscus
from an angle
Measuring Volume
Determine the volume contained in a graduated cylinder by reading the bottom of the meniscus at eye level.
Read the volume using all certain digits and one uncertain digit.
Certain digits are determined from the calibration marks on the cylinder.
The uncertain digit (the last digit of the reading) is estimated.
Use the graduations to find all certain digits
There are two unlabeled graduations below the meniscus, and each graduation represents 1 mL, so the certain digits of the reading are…
52 mL.
Estimate the uncertain digit and take a reading
The meniscus is about eight tenths of the way to the next graduation, so the final digit in the reading is .
The volume in the graduated cylinder is
0.8 mL
52.8 mL.
10 mL GraduateWhat is the volume of liquid in the graduate?
_ . _ _ mL6 _6
25mL graduated cylinder What is the volume of liquid in the graduate?
_ _ . _ mL1 1
Self TestExamine the meniscus below and determine the volume of liquid contained in the graduated cylinder.
The cylinder contains:
_ _ . _ mL
Reading the ThermometerDetermine the readings as shown below on Celsius thermometers:
_ _ . _ C _ _ . _ C
Using the Balance• Use the On/Off Zero button to zero
the balance.• Use the Cal/Unit button to change
the units: g is grams, oz is ounces, ozt is troy ounces, and dwt is pennyweights.
Reporting Measurements: Once Again
• Report the digit for the unit that is known with certainty
• Add ONE digit of uncertainty (estimation)
• Even if the uncertain digit is 0, it still must be reported.