I. Scientific Method
Dec 27, 2015
The Scientific MethodA logical approach to solving problems or answering questions.
Starts with observation- noting and recording information and facts
hypothesis- educated guess or testable statement
Steps in the Scientific Method1. Observations (uses your senses)
a) quantitative involves numbers = 95oF
b) qualitative is word description = hot
2. Formulating hypotheses (ideas)3. Performing experiments (the test)
- gathers new information to help decide whether the hypothesis is valid
Scientific Method Controls- constants Variables- changing conditions
Limit variables We gather data and observations
by doing the experiment Modify hypothesis - repeat the
cycle based on results
Steps in the Scientific MethodTheorize (model)
- explanation of some natural phenomenonMany phenomena- construct a theory
Publish Results- Do other experts agree
SI Units
Quantity Base Unit Abbrev.
Length
Mass
Time
Temp
meter
kilogram
second
kelvin
m
kg
s
K
Amount mole mol
Symbol
l
m
t
T
n
SI Units
mega- M 106
deci- d 10-1
centi- c 10-2
milli- m 10-3
Prefix Symbol Factor
micro- 10-6
nano- n 10-9
pico- p 10-12
kilo- k 103
BASE UNIT --- 100
Derived UnitsCombination of base units.
Volume (m3 or cm3) length length length
D = MV
1 cm3 = 1 mL1 dm3 = 1 L
Density (kg/m3 or g/cm3)mass per volume
DensityAn object has a volume of 825 cm3 and a density of
13.6 g/cm3. Find its mass.
GIVEN:
V = 825 cm3
D = 13.6 g/cm3
M = ?
WORK:
M = DV
M = (13.6 g/cm3)(825cm3)
M = 11,200 g
V
MD
DensityA liquid has a density of 0.87 g/mL. What volume is
occupied by 25 g of the liquid?
GIVEN:
D = 0.87 g/mL
V = ?
M = 25 g
WORK:
V = M D
V = 25 g
0.87 g/mL
V = 29 mLV
MD
Accuracy vs. PrecisionAccuracy - how close a measurement is to
the accepted value
Precision - how close a series of measurements are to each other
ACCURATE = CORRECT
PRECISE = CONSISTENT
Percent ErrorIndicates accuracy of a measurement
100literature
literaturealexperimenterror %
your value
accepted value
Percent ErrorA student determines the density of a
substance to be 1.40 g/mL. Find the % error if the accepted value of the density is 1.36 g/mL.
100g/mL 1.36
g/mL 1.36g/mL 1.40error %
% error = 2.9 %
Significant FiguresIndicate precision of a measurement.
Recording Sig FigsSig figs in a measurement include the known digits plus a final estimated digit
2.35 cm
Significant FiguresCounting Sig Figs (Table 2-5, p.47)
Count all numbers EXCEPT:Leading zeros -- 0.0025
Trailing zeros without a decimal point -- 2,500
4. 0.080
3. 5,280
2. 402
1. 23.50
Significant FiguresCounting Sig Fig Examples
1. 23.50
2. 402
3. 5,280
4. 0.080
4 sig figs
3 sig figs
3 sig figs
2 sig figs
Significant FiguresCalculating with Sig Figs
Multiply/Divide - The # with the fewest sig figs determines the # of sig figs in the answer.
(13.91g/cm3)(23.3cm3) = 324.103g
324 g
4 SF 3 SF3 SF
Significant FiguresCalculating with Sig Figs (con’t)
Add/Subtract - The # with the lowest decimal value determines the place of the last sig fig in the answer.
3.75 mL
+ 4.1 mL
7.85 mL
224 g
+ 130 g
354 g 7.9 mL 350 g
3.75 mL
+ 4.1 mL
7.85 mL
224 g
+ 130 g
354 g
Significant FiguresCalculating with Sig Figs (con’t)
Exact Numbers do not limit the # of sig figs in the answer.Counting numbers: 12 studentsExact conversions: 1 m = 100 cm“1” in any conversion: 1 in = 2.54 cm
Significant Figures
5. (15.30 g) ÷ (6.4 mL)
Practice Problems
= 2.390625 g/mL
18.1 g
6. 18.9 g
- 0.84 g18.06 g
4 SF 2 SF
2.4 g/mL2 SF
Scientific Notation
Converting into Sci. Notation:
Move decimal until there’s 1 digit to its left. Places moved = exponent.
Large # (>1) positive exponentSmall # (<1) negative exponent
Only include sig figs.
65,000 kg 6.5 × 104 kg
Scientific Notation
7. 2,400,000 g
8. 0.00256 kg
9. 7 10-5 km
10. 6.2 104
mm
Practice Problems
2.4 106 g
2.56 10-3 kg
0.00007 km
62,000 mm
Scientific NotationCalculating with Sci. Notation
(5.44 × 107 g) ÷ (8.1 × 104 mol) =
5.44EXPEXP
EEEE÷÷
EXPEXP
EEEE ENTERENTER7 8.1 4
= 671.6049383 = 670 g/mol = 6.7 × 102 g/mol
Type on your calculator:
3
3
cm
gcm
Dimensional AnalysisThe “Factor-Label” Method
Units, or “labels” are canceled, or “factored” out
g
Dimensional AnalysisSteps:
1. Identify starting & ending units.
2. Line up conversion factors so units cancel.
3. Multiply all top numbers & divide by each bottom number.
4. Check units & answer.
Dimensional AnalysisLining up conversion factors:
1 in = 2.54 cm
2.54 cm 2.54 cm
1 in = 2.54 cm
1 in 1 in
= 1
1 =
Dimensional AnalysisHow many milliliters are in 1.00 quart of milk?
1.00 qt 1 L
1.057 qt= 946 mL
qt mL
1000 mL
1 L
Dimensional AnalysisYou have 1.5 pounds of gold. Find its volume
in cm3 if the density of gold is 19.3 g/cm3.
lb cm3
1.5 lb 1 kg
2.2 lb= 35 cm3
1000 g
1 kg
1 cm3
19.3 g
Dimensional Analysis Your European hairdresser wants to cut your
hair 8.0 cm shorter. How many inches will he be cutting off?
8.0 cm 1 in
2.54 cm= 3.2 in
cm in
Dimensional Analysis Taft football needs 550 cm for a 1st down. How
many yards is this?
550 cm 1 in
2.54 cm= 6.0 yd
cm yd
1 ft
12 in
1 yd
3 ft
Dimensional AnalysisA piece of wire is 1.3 m long. How many 1.5-cm
pieces can be cut from this wire?
1.3 m 100 cm
1 m= 86 pieces
cm pieces
1 piece
1.5 cm