2. SCIENTIFIC METHOD CHEM 04

3. A series of logical steps to follow to solve problems Define the Scientific Method:

4. You cannot solve a problem until you know exactly what it is. Look at the world around you to make observations. My Problem is - “How long does it take to receive a text message on your cell phone?” Step 1: State the problem

5. Types of Observations When you make observations there are two types : –Quantitative – observations based on numeric value (the grass is 5 cm tall) –Qualitative – observations based on descriptive terms ( the grass is green)

6. What will it take to solve my problem? What do I know, and need to know, about my problem? To solve my problem, - Examine the possibilities. - Eliminate poor choices. - Consider likely choices. Step 2: Research the problem

7. Step 3: Form a hypothesis A possible solution to my problem. The simplest solution is often the best solution! Increasing/decreasing the MV will increase/decrease the RV

8. Perform an experiment to see if your hypothesis works. Step 4: Test the hypothesis

9. Controlled Experiment: Variable - The factor being tested in an experiment. Independent (manipulated) – factor adjusted by the experimenter Dependent (responding) – factor whose value depends upon the value of the independent variable

10. Data are the results of an experiment. In its simplest form, there are only two possibilities: –(1) If your hypothesis was correct, PROBLEM SOLVED! –(2) If your hypothesis was incorrect, the experiment failed. DON'T GIVE UP! DO MORE RESEARCH! - What was wrong with your original hypothesis? - Did you make a poor selection? - Was your experiment flawed? - Form another hypothesis based on additional research. - Test your new hypothesis. Step 5: Draw conclusions from the data

11. Continue this process until the problem is solved! If the hypothesis is proven to be incorrect, you must find out what was wrong with it. This might lead to the formation of a hypothesis about the hypothesis!

12. Scientific Theory A logical explanation of observed events, based on repeated experimentation.

13. Scientific LAW Sums up related observations and experimental results to describe a pattern in nature.

14. Controlled Experiment:. Control - A part of the experiment without the variable. This part of the experiment is used as a comparison. Data - Observations from the experiment. Constant – factor that does not change or vary in an experiment

15. Accuracy the closeness of measurements to the correct or accepted value of the quantity measured

16. Precision the closeness of a set of measurements of the same quantity made in the same way

17. Can you hit the bulls eye?

18. Accepted Value – based on reliable references Experimental Value – measured in the lab –Error = experimental – accepted Positive value – accepted value is greater than he experimental value Negative value – accepted value is less than the experimental value –Percent error = | value accepted – value experimental | x 100% Value accepted

19. Example: –A student measures the mass and volume of a substance and calculates its density as 1.40g/mL. The correct, or accepted, value of the density is 1.36g/mL. What is the percent error? %error = | 1.36g/mL – 1.40g/mL | 1.36g/mL X 100 = -2.9 % error

20. Significant Digits consist of all of the digits known with certainty plus one final digit that is estimated Many experiments in science involve measuring different quantities. No matter how carefully scientists measure something, there is always a limit to how exact, or precise, a measurement is. This limits how precise the results of the experiment are. For this reason, scientists use significant figures to keep track of the precision of their calculations.