Unit 1Scientific Method

+Measurement

Chem 1Fall 07

Scientific Method

Scientific Method (cont.)• People often confuse

– Observations & Hypotheses

• An observation…– Is information

collected with the senses

• A hypothesis…– Is a theory about the

natural world that needs to be tested

Ivan Pavlov observed dogs salivating and

hypothesized that a sound would cause

dogs to salivate.

Scientific Method (cont.)

• People also often confuse– Controls & Variables

• A control is…– A trial that duplicates all conditions except

the variable being investigated• A variable is…

– The thing being tested

Practice Problem #1• Identify the following as an observation or a

hypothesis– 1. Wearing tennis shoes will make one run faster.

– 2. The tennis shoes are black and red.

– 3. The Bunsen Burner flame is 1400°C and is blue.

– 4. People who take good notes will do better on tests.

Hypothesis

Observation

Observation

Hypothesis

Types of Observations

• Scientists make observations all the time.• There’s two types:

– Qualitative– Quantitative

• To remember the difference, look at their root

Qualitative Observations

• Qualities of the reaction, object, etc.• Example

– The copper (II) sulfate is blue– The nail is rusty– Gas was given off

Quantitative Observations

• Quantity= numbers• Mass, a number of paper clips, volume

measurements, molar measurements. • Math is usually involved

Metrics

• Metric system is much easier than the English system…the conversion is always a factor of 10.

Length is a 1-dimensional measure of distance. Metric system base unit is the

meter, abbreviated m

Metrics (cont.)• Mass is a measure of the amount of

matter in a substance.– Metric system base unit is the

kilogram, abbreviated kg

Volume is a measure of the amount of space a substance takes up.

Metric system base unit is the liter, abbreviated L.

Weight• Response of

mass to the pull of gravity

• Weight changes when on different planets

• NOT THE SAME AS MASS!

Metrics (cont.)

• Kilo hecto deka (m, g, L) deci centi milli• k h dk or D d c m

– How do you remember the order of the prefixes?

Metric Prefixes

Kilo hecto deka (m, g, L) deci centi milli k h dk d c m

103 102 101 10-1 10-2 10-3

How do you remember the order of the prefixes?

Practice Problem #2

• Make the following metric conversions– 1. 875 cm = _________ m.

– 2. 1.24 km = _________ m.

– 3. 90,344 m = _________ km.

– 4. 0.95 km = _________cm.

9.75

1,240

90.344

950,000

Accuracy and Precision

• Accuracy– Close to the true

or desired value• Precision

– Reproducible measurements

Measurement• There is always an

error in a measurement

• The human eye can read one decimal place beyond the accuracy of the instrument

The measurement should be read as 8.0 +/-0.1cm.

Practice Problem #3

65

60

55

10

9

8

150

100

50

Container #1 Container #2 Container #39.02 mL 82 mL 62.0 mL

Read the volumes of the liquids below