SCIENTIFIC METHODSCIENTIFIC METHODCHEM 04CHEM 04

A series of logical steps to follow to solve problems

Define the Scientific Method:

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

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)

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

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

• Perform an experiment to see if your hypothesis works.

Step 4:Test the hypothesis

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

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

Continue this process until the problem is solved!

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!

Scientific Theory

A logical explanation of observed events, based

on repeated experimentation.

Scientific LAW

• Sums up related observations and experimental results to describe a pattern in nature.

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

Accuracy the closeness of measurements to

the correct or accepted value of the quantity measured

Precision the closeness of a set of measurements of the same

quantity made in the same way

Can you hit the bulls eye?

• 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

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

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. Nomatter 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.