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 Processes Section 1.2: Observations & Measurements Section 1.3: Designing Labs Section 1.4: Converting Units Section 1.5: Significant digits Section 1.6: Scientific Notation

Chemistry is an Experimental Science Although no one method, there are Design your own labs Are used when you Common characteristics Unit conversions May require include Accurate & precise measurements When using in calculations, follow Careful observations Significant digit rules Scientific Notation 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 use Questioning & Observing Gathering Data Experimentation Field Studies Long-term observations Surveys Literature reviews & more Analyzing all the data Using evidence & logic to draw conclusions Communicating findings

Science is “loopy” 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 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!

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 value What is the value of the gas law constant? What is the concentration of that salt solution?

How does reaction rate change with temperature Variables depends on Independent Variable Dependent Variable Controlled by you You measure or observe Example: How does reaction rate change with temperature

How does reaction rate change with temperature Variables depends on Independent Variable Dependent Variable Controlled by you You measure or observe Example: How does reaction rate change with temperature Temperature Reaction rate

What is the concentration of that salt solution? Variables Independent Variable Dependent Variable Example: What is the concentration of that salt solution?

What is the concentration of that salt solution? Variables Variables are not appropriate in specific value experiments Independent Variable Dependent Variable Example: What is the concentration of that salt solution? Not appropriate

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 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 reactants Example: How does reaction rate change with temperature And maybe you thought of some others! Volumes of reactants Method of determining rate of reaction

Prediction versus Hypothesis They are different! Prediction Hypothesis Just predicts Attempts to explain why you made that prediction Example: How does surface area affect reaction rate?

Prediction versus Hypothesis They are different! Prediction Hypothesis Just predicts Attempts 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 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 Prediction Hypothesis Example: What is the concentration of that salt solution? Not appropriate—it would just be a random guess

Describe each group’s data as not precise, precise or accurate 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

Precise & Accurate Data Precise, but not accurate Correct value Example: Describe each group’s data as not precise, precise or accurate Precise & Accurate Correct value Not precise Correct value

Can you be accurate without precise? This group had one value that was almost right on…but can we say they were accurate? Correct value

Can you be accurate without precise? This group had one value that was almost right on…but can we say they were accurate? Correct value No…they weren’t consistently correct. It was by random chance that they had a result close to the correct answer.

“Within Experimental Error” 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. You have to decide if the variance in your results is within acceptable experimental error Correct value

Drawing Conclusions 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.

Theory versus Law Many people do not understand the difference between these two terms Cannot ever become Theory Law Describes why something occurs Describes or predicts what happens (often mathematical) Example: The relationship between pressure and volume

Theory versus Law Many people do not understand the difference between these two terms Cannot ever become Theory Law 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

Communicating Results 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 conference Articles in journals Online collaboration & discussions Collaboration between separate groups working on similar problems