An introduction. In our daily lives: New materials New pharmaceuticals New energy sources Food...

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