CHEMISTRY = the study of the composition of matter, its chemical and physical changes, and the changes that accompany these changes.

DEMO

• The Think Tube

• Chemistry is all about trying to figure out things you can’t necessarily see.

The Nature of Science

• Scientific law versus theory:

– Scientific law: a summary of an observed natural event.

– Scientific theory: a well tested, possible explanation of a natural event.

The Way Science Works…

• Science involves critical thinking, or applying logic and reason to observations and conclusions.

• Observation vs. Inference– Observation: descriptive of what you

see, hear, taste, feel, smell– Inference: an assumption made as a

result of an observation (not always correct!!)

Variables and Controls• A variable is anything that can change in an

experiment.

– Independent variable: The variable being changed or controlled by the scientist.

– Dependent variable: The variable being measured or observed by the scientist.

• A controlled experiment tests only one variable at a time.

DEMO

• On the Level

• The Unknown Bubble

The Scientific Method:A series of logical steps to follow in order to solve problems.

• OBSERVE• FORMULATE A QUESTION• FORM A HYPOTHESIS• DESIGN AND CONDUCT AN EXPERIMENT• MAKE OBSERVATIONS• RECORD AND ANALYZE DATA• DRAW CONCLUSIONS• FORMULATE NEW QUESTIONS and

CONTINUE CYCLE

Making Measurements• Measurements are made in this class using SI

units.

• LENGTH (m): distance between 2 points

• VOLUME (L): space occupied.

• MASS (kg): the amount of matter in an object.

• WEIGHT (N): the force with which gravity pulls on a quantity of matter.

Precision vs. Accuracy

• Accuracy: the extent to which a measurement approaches the true value.

• Precision: the degree of exactness of a measurement. – A scale may be precise to the nearest

100th of a gram, or +/- 0.01g

Precision vs. Accuracy

increasing accuracy

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pre

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Density = mass/volume• Example:

– What is the mass of 10 mL of a liquid that has a density of 3.76 g/mL?

d = m / v m = dvm = (3.76 g/mL)(10 mL)m = 37.6 gm = 40 g (correct # of sig.

figs.)

M

D V

Coke vs. Diet Coke

• Which is less dense? Meaning which will float in water?

• Coke or Diet Coke?

WHY is Diet Coke less dense?

• There is less mass in the same volume (355 mL)

• Coke has 39 grams of sugar in it to sweeten it (355 + 39 = 394 g)

• Diet Coke only needs 0.1 g of Nutra Sweet to make is just as sweet as Coke (355 + 0.1 = 355.1 g)

Temperature Conversions

• Temperature is a measure of the average kinetic energy in a system.

• K = Kelvin• oF = degree Fahrenheit• oC = degree Celsius• R=Rankin (we won’t use this one in this

class)

Temperature Conversions

• K = oC + 273

• oF = (1.8 x oC) + 32

• oC = (oF – 32) / 1.8

Percentage Error

• Calculate this value in labs where the accepted value is given.

010 valueaccepted

valuemeasured valueacceptederror %

Graph - visual representation of data1) title2) x and y axis labeled3) units for both the x and y axis4) scale is evenly and correctly spaced for data5) legend when appropriate

Organizing DataData is organized and presented in tables, charts, and graphs.

LINE GRAPH: best for displaying data that change.– Independent Variable: x-axis– Dependent variable: y-axis

Temperature Increase of a Beaker of Water

250

300

350

400

450

0 50 100 150 200 250 300 350 400

Time (sec)

Tem

pera

ture

(K)

BAR GRAPH: useful when you want to compare data for several individual items

Leading Causes of Death in 2000

300

233

107 9857

0

50

100

150

200

250

300

350

HeartDisease

Cancer Diabetes Accidents HomicideNu

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PIE CHART: ideal for displaying data that are parts of a whole.

Favorite Television Shows among Teens

45%

30%

20%

4%

1%

Friends

Will and Grace

Frasier

Dawson's Creek

Other