Unit 1 Scientific Method + Measurement Chem 1 Fall 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 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 How do you remember the order of the prefixes?

Practice Problem #2 Make the following metric conversions – cm = _________ m. – km = _________ m. –3. 90,344 m = _________ km. – km = _________cm , ,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 # Container #1 Container #2Container # mL82 mL62.0 mL Read the volumes of the liquids below