Introduction to Chemistry

Branches of ChemistryScientific Method

Experimental Design

Q: Why are chemists great at solving problems?

A: They have all the solutions!!!

Chemistry Joke

Organic◦ Associated with CARBON compounds.

Inorganic◦ Associated with NON-CARBON compounds.

Analytical◦ Associated with the COMPOSITION of samples

Physical◦ Associated with the BEHAVIOR/ENERGY of

compounds Biochemical

◦ Associated with the chemistry of LIFE

Branches of Chemistry

A logical, systematic approach to the solution of a scientific problem.

Steps in the scientific method include:1.Making observations2.Formulating hypotheses 3.Testing hypothesis through

experimentation4.Developing theories or

formulating laws.

The Scientific Method1.3

1. Making Observations

◦When you use your senses to obtain information, you make an observation.

The Scientific Method1.3

2. Formulating Hypotheses

– A hypothesis is a proposed explanation for an observation.

3. Testing Hypotheses through Experimentation

The Scientific Method1.3

An experiment is a procedure that is used to test a hypothesis.

The experimental design is critical to the reliability of the results.

We should have only one manipulated variable and one dependent variable.

◦We want to test the effect of the manipulated variable on the dependent variable.

◦For example: The effect of surface area on solubility The effect of temperature on pressure

Experimental Design

Experimental DesignD

RY

MIX

Dependent Variable

Relies on the Other

Y-axis

Manipulated Variable

Independent

X-axis

We often graph our results.

The manipulated variable will be on the x-axis.The dependent variable will be on the y-axis.

Our results can show a direct relationship or an indirect/inverse relationship.

Experimental Design

DIRECT (X/Y)

INDIRECT (XY)

We should be careful to change only one variable.

◦For example, use the same equipment for each trial.

◦Conduct each trial under the same conditions.

Experimental Design

We should have a control.◦ This is a trial in which the manipulated variable

is not changed—used for comparison. We should average the results of many

trials.◦ To find the mean, add the results of each trial

and divide by the total number of trials. ◦ More trials produce better reliability of results.

Results should be reproducible by other scientists.

We should report all results, not just the expected ones.

Experimental Design

Chemists often use probeware to measure such things as pH, temperature, or pressure.◦ The probes connect to a computer and

the data is graphed automatically.

Experimental Design

Computer simulations are also often used to test theories.

4. Developing Theories Once a hypothesis meets the test of

repeated experimentation, it may become a theory.

A theory is a loooong explanation for WHY something happens.

A theory may need to be changed at some point in the future to explain new observations or experimental results.

The Scientific Method1.3

4. Formulating Scientific Laws

A scientific law is a short mathematical statement of WHAT happens.

A scientific law doesn’t try to explain the relationship it describes. That explanation requires a theory.

The Scientific Method1.3

Steps in the Scientific Method

Chemistry Joke

Q: What substance has the formula HIJKLMNO?

A: Water (H to O)!!!