Chemistry BasicsPart 6

Ray Tedder

NBC Chemistry Teacher

Chemistry Basics

Indicator C-1.4• According to Indicator C-1.4 in the South

Carolina Science Standards students should be able to design a scientific investigation with appropriate methods of control to test a hypothesis (including independent and dependent variables), and evaluate the designs of sample investigations.

Chemistry Basics

Goal of Science:

Generating hypotheses from

a model.

Organizing what we know, and what we’d like

to know.

Seeking evidence to test

hypotheses.

Constructing an argument.

To develop defendable arguments to explain the way the universe works.

These arguments must be based upon physical evidence, physical explanations and sound

reasoning.

Chemistry BasicsModel• A proposed explanation of why observed

behaviors occur. – Models describe how the how the universe

works.• Models that have yet to be tested are proposed

models. • Models that have been tested are tested models.• Models that have been repeated tested and are

accepted as valid by most scientists are called theories.

Chemistry BasicsModel• In chemistry we usually look at little tiny

pieces of the universe at a time. – Most often in chemistry models explain

behavior we observe in ways that we cannot see .• Models often attempt to explain why behavior

occurs by imagining how things we cannot see are causing things we do see.

Chemistry BasicsHypothesis• A proposed test for a model

– In this class an hypothesis is only valid if it has an “if/then” or “cause/effect” form.• The “if” or “cause” part of an hypothesis statement

must summarize the independent variable. • The “then” or “effect” part of an hypothesis

statement must summarize the dependent variable.

Chemistry BasicsHypothesisExample:• If the diffusion rate through a membrane is

related to molecular size, then the smaller the molecule the faster it will pass through a membrane.

biology or chemistry (depending on type of membrane)

Chemistry BasicsHypothesisExample:• If the diffusion rate through a membrane is

related to molecular size, then the smaller the molecule the faster it will pass through a membrane.– The highlighted part of the hypothesis

statement is the “if” part, indicating that the size of molecules is the independent variable.

biology or chemistry (depending on type of membrane)

Chemistry BasicsHypothesisExample:• If the diffusion rate through a membrane is

related to molecular size, then the smaller the molecule the faster it will pass through a membrane.– The independent variable is the part that you

change in the experiment.– In your experiment you will you change the

size if the molecules used.

biology or chemistry (depending on type of membrane)

Chemistry BasicsHypothesisExample:• If the diffusion rate through a membrane is

related to molecular size, then the smaller the molecule the faster it will pass through a membrane.

biology or chemistry (depending on type of membrane)

Chemistry BasicsHypothesisExample:• If the diffusion rate through a membrane is

related to molecular size, then the smaller the molecule the faster it will pass through a membrane.

biology or chemistry (depending on type of membrane)

Chemistry BasicsHypothesisExample:• If the diffusion rate through a membrane is

related to molecular size, then the smaller the molecule the faster it will pass through a membrane.– The highlighted part of the hypothesis

statement is the “then” part, indicating that the diffusion rate through some membrane will be the independent variable.

biology or chemistry (depending on type of membrane)

Chemistry BasicsHypothesisExample:• If the diffusion rate through a membrane is

related to molecular size, then the smaller the molecule the faster it will pass through a membrane.– The independent variable is the part that

changes because you changed the dependent variable.

biology or chemistry (depending on type of membrane)

Chemistry BasicsHypothesisExample:• If the diffusion rate through a membrane is

related to molecular size, then the smaller the molecule the faster it will pass through a membrane.– You will measure this independent variable by

measuring how fast molecules move from one side of the membrane to the other.

biology or chemistry (depending on type of membrane)

Chemistry BasicsHypothesisExample:• If the diffusion rate through a membrane is

related to molecular size, then the smaller the molecule the faster it will pass through a membrane.– What evidence would support this

hypothesis?– What evidence would disprove this

hypothesis?

biology or chemistry (depending on type of membrane)

Chemistry BasicsHypothesisExample:• If the temperature of a cup of water is

raised, then the amount of sugar that dissolves will increase.

chemistry

– Can you identify the independent and dependent variables?

– Can you suggest how this experiment might be set up?

Chemistry BasicsHypothesisExample:• If the temperature of a cup of water is

raised, then the amount of sugar that dissolves will increase.

chemistry

– What evidence would support this hypothesis?

– What evidence would disprove this hypothesis?

Chemistry BasicsHypothesisExample:• If the rate of photosynthesisis related to

wavelengths of light, then exposing a plant to different colors of light will produce different amounts of oxygen.

biology

– Can you identify the independent and dependent variables?

– Can you suggest how this experiment might be set up?

Chemistry BasicsHypothesisExample:• If the rate of photosynthesisis related to

wavelengths of light, then exposing a plant to different colors of light will produce different amounts of oxygen.

biology

– What evidence would support this hypothesis?

– What evidence would disprove this hypothesis?

End