Unit 1 Scientific Method + Measurement

Unit 1Scientific Method+Measurement Chem 1 Fall 07

Scientific Method

Ivan Pavlov observed dogs salivating and hypothesized that a sound would cause dogs to salivate. 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

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 hectodeka (m, g, L) decicentimilli 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.

Read the volumes of the liquids below Practice Problem #3 9.02 mL 82 mL 62.0 mL Container #1 Container #2 Container #3 10 150 65 9 100 60 8 50 55

Unit 1 Scientific Method + Measurement