Chapter 1: Scientists’ Tools

Chemistry is an Experimental Science

This chapter will introduce the following tools that scientists use to “do chemistry”Section 1.1: Scientific ProcessesSection 1.2: Observations & MeasurementsSection 1.3: Designing LabsSection 1.4: Converting UnitsSection 1.5: Significant digitsSection 1.6: Scientific Notation

Chemistry is an Experimental Science

Common characteristic

s

Common characteristic

s

Although no one method, there are

Careful observation

s

Careful observation

s

Accurate & precise

measurements

Accurate & precise

measurements

Design your own labs

Design your own labs

Unit conversions

Unit conversions

Significant digit rules

Significant digit rules

Scientific Notation

Scientific Notation

Are used when you

include

May require

When using in calculations, follow

May require using

Section 1.1—Doing Science

There is no “The Scientific Method”

There is no 1 scientific method with “X” number of steps

There are common processes that scientists useQuestioning & ObservingGathering Data

ExperimentationField StudiesLong-term observationsSurveysLiterature reviews& more

Analyzing all the dataUsing evidence & logic to draw conclusionsCommunicating findings

Science is “loopy”

Science is not a linear process…rather it is “loopy”…and it’s not just about experimentation

…there are many pathways…even more than are shown here!

Observations

Questions

Data gathering (experiment, literature

research, field observations, long-term studies, etc.)

Hypothesis

Trend and pattern recognition

Conclusion formation

Communication & Validation

Model Formation

Product or technology formation

Two types of Experiments

This text will predominantly use experimentation for data gathering

Two types of experiments will be used:To investigate relationships or effect

How does volume affect pressure?How does reaction rate change with temperature?

To determine a specific valueWhat is the value of the gas law constant?What is the concentration of that salt solution?

Variables

Dependent VariableIndependent Variable

Controlled by youYou measure or

observeExample:How does reaction

rate change with

temperature

depends on

Variables

Dependent VariableIndependent Variable

Controlled by youYou measure or

observeExample:How does reaction

rate change with

temperature

Temperature Reaction rate

depends on

Variables

Dependent VariableIndependent Variable

Example:What is the concentration of that salt

solution?

Variables

Variables are not appropriate in specific value experiments

Dependent VariableIndependent Variable

Example:What is the concentration of that salt

solution?

Not appropriate

Constants

It’s important to hold all variables other than the independent and dependent constant so that you can determine what actually caused the change!

Constants

Example:How does reaction

rate change with

temperature

Constants

It’s important to hold all variables other than the independent and dependent constant so that you can determine what actually caused the change!

Constants

Concentrations of reactantsExample:

How does reaction

rate change with

temperature

Volumes of reactants

Method of determining rate of

reaction

And maybe you thought of some others!

Prediction versus Hypothesis

They are different!HypothesisPrediction

Just predictsAttempts to explain why you made that prediction

Example:How does

surface area affect

reaction rate?

Prediction versus Hypothesis

They are different!HypothesisPrediction

Just predictsAttempts to explain why you made that prediction

Example:How does

surface area affect

reaction rate?

Reaction rate will increase as surface

area increases

Reaction rate will increase with surface area because more molecules can have

successful collisions at the same time if more can come in contact

with each other.

Predictions versus Hypothesis

HypothesisPrediction

Example:What is the concentration of that salt

solution?

Predictions versus Hypothesis

It is not appropriate to make a hypothesis or prediction in specific value experiments

HypothesisPrediction

Example:What is the concentration of that salt

solution?

Not appropriate—it would just be a random guess

Gathering Data

Multiple trials help ensure that you’re results weren’t a one-time fluke!

Precise—getting consistent data within experimental error

Accurate—getting the “correct” or “accepted” answer consistently

Example:Describe

each group’s data as not

precise, precise or accurate

Correct value

Correct value

Correct value

Precise & Accurate Data

Example:Describe

each group’s data as not

precise, precise or accurate

Correct value

Correct value

Correct value

Precise, but not accurate

Precise & Accurate

Not precise

Can you be accurate without precise?

Correct value

This group had one value that was almost right on…but can we say they were

accurate?

Can you be accurate without precise?

Correct value

This group had one value that was almost right on…but can we say they were

accurate?

No…they weren’t consistently correct. It was by random chance that they had a result

close to the correct answer.

Precise is consistent within experimental error.

What does that mean?Every measurement has some error in it…we

can’t measure things perfectly. You won’t get exactly identical results each time.

“Within Experimental Error”

Correct value

You have to decide if the variance in your results is within acceptable

experimental error

Scientists take into account all the evidence from the data gathering and draw logical conclusions

Conclusions can support or not support earlier hypothesis

Conclusions can lead to new hypothesis, which can lead to new investigations

As evidence builds for conclusions, theories and laws can be formed.

Drawing Conclusions

Theory versus Law

Many people do not understand the difference between these two terms

LawTheory

Describes why something occurs

Describes or predicts what happens (often mathematical)

Example:The

relationship between pressure

and volume

Cannot ever become

Theory versus Law

Many people do not understand the difference between these two terms

LawTheory

Describes why something occurs

Describes or predicts what happens (often mathematical)

Example:The

relationship between pressure

and volume

Kinetic Molecular Theory—as volume decreases, the frequency of collisions with the wall will increase & the

collisions are the “pressure”

Boyle’s Law:P1V1 = P2V2

Cannot ever become

Scientists share results with the scientific community to:Validate findings (see if others have similar results)Add to the pool of knowledge

Scientists use many ways to do this:Presentations and posters at conferenceArticles in journalsOnline collaboration & discussionsCollaboration between separate groups working on

similar problems

Communicating Results