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an introduction
In our daily lives: New materials New pharmaceuticals New energy sources Food supplies
Can you think of anything else?
Is the science that deals with the materials of the universe and the changes that those materials undergo
What are some examples of chemical changes? Iron rusting Wood burning Food cooking Grape juice fermenting Plants growing
How do we know that these are chemical changes?
1. Observations Quantitative vs Qualitative
Quantitative – measurement involves a number and a unit
2. Formulating Hypotheses Possible explanation for the observation
3. Performing Experiments Gathering new information to decide whether
the hypothesis is valid
Qualitative Quantitativered book 4 quartersround tire 6 wheelswooden desk 24 studentsmetal chair 5 atomsaluminum foil 65°Cglass square 2” x 4” x 8”rough board 2 graduated cylinders
Theory (Model) A set of tested hypotheses that give an overall
explanation of some natural phenomenon
Natural Law The same observation applies to many
different systems Ex. Law of Conservation of Mass
A law summarizes what happens; a theory (model) is an attempt to explain why it happens
01_03
Observation
Hypothesis
Experiment
Theory(model)
Experiment
Theorymodifiedas needed
Prediction
Law
Scientists must be objective when using the scientific method. The scientific method is affected by:Profit motives Religious BeliefsWars Misinterpretation of
DataBudgets EmotionsFads PrejudicesPolitics Peer Pressure
What is the difference between a hypothesis and a theory?
What is the difference between an observation and a theory?
What is the difference between a natural law and a theory?
Physical Quantity Name Abbreviationmass kilogram kglength meter mtime second stemperature Kelvin KElectric Current Ampere AAmount of Substance mole molLuminous Intensity candela cd
Prefix Unit Abbr. ExponentMega M 106
Kilo k 103
Deci d 10-1
Centi c 10-2
Milli m 10-3
Micro µ 10-6
Nano n 10-9
Pico p 10-12
A digit that must be estimated is called uncertain. A measurement always has some degree of uncertainty. Measurements are performed with
instruments No instrument can read to an infinite number
of decimal places.
Accurate and precise
Precise, but not accurate
Neither accurate not precise
Accuracy refers to the agreement between the measure quantity and the accepted value
Precision refers to the degree of agreement of several repeated measurements (made in the same manner) to each other.
Random Error (Indeterminate Error) – Measurement has an equal probability of
being high or low
Systematic Error (determinate Error) – Occurs in the same direction each time (high
or low), often resulting from poor technique or incorrect calibration. This can result in measurements that are
precise, but not accurate
Non-zero integers always count as sig. fig.
34564 sig figs
Zeros Leading Zeros do not count as sig figs
0.04863 sig figs
Zeros Captive Zeros always count as sig figs
16.074 sig figs
Zeros Trailing Zeros are significant only if the
number contains a decimal point.
9.3004 sig figs
Exact Numbers have an infinite number of significant figures.
1 inch = 2.54 cm
1.0070 m17.10 kg100,890 L
3.29 x103 s 0.0054 cm3, 200, 000
5 sig figs4 sig figs5 sig figs3 sig figs2 sig figs2 sig figs
Multiplication and Division number of sig figs in the results equals the
number of sig figs in the least precise measurement used n the calculation (the one with the lowest number of sig figs).
6.38 x 2.0 = 12.76 6.38 x 2.0 = 12.76
13 (2 sig figs)13 (2 sig figs)
Calculation Calculator Says
3.24 m x 7.0 m 22.68 m2
100.0 g ÷ 23.7 cm3 4.219409283 g/cm3
0.02 cm x 2.371 cm 0.04742 cm2
710 m ÷ 3.0 s 236.6666667 m/s
1818.2 lb x 3.23 ft 5872.786 lb·ft
1.030 g ÷ 2.87 mL 2.9561 g/mL
Answer23 m2
4.22 g/cm3
0.05 cm2
240 m/s
5870 lb·ft
2.96 g/mL
Addition and Subtraction The number of decimal places in the result
equals the number of decimal places in the least precise measurement
6.8 + 11.934 = 18.734 6.8 + 11.934 = 18.734
18.7 18.7 (3 sig figs)(3 sig figs)
Calculation Calculator Says
3.24 m + 7.0 m 10.24 m2
100.0 g - 23.73 cm3 76.27 g/cm3
0.02 cm + 2.371 cm
2.391 cm2
713.1 m – 3.827 s 709.228 m/s
1818.2 lb + 3.37 lb 1821.57 lb·ft
2.030 mL - 1.870 mL
0.16 g/mL
Answer10.2 m
76.3 g
2.39 cm
709.2 L
1821.6 lb
0.160 mL