1. Dimensional Analysis & Unit Conversions
CHEMISTRY I
Scientific Inquiry
Measurement
Dimensional Analysis & Unit Conversions
Significant Digits

2. These Notes Cover: Scientific Inquiry Measurement Law vs. Theory
Scientific Methods & Experimental Design
Different Branches of Science
Measurement
Accuracy vs. Precision
Units of Measure & Unit Conversions
Estimated Digit & Significant Digits
Scientific Notation

3. Scientific Inquiry – Law vs. Theory
Scientific laws STATE what happens
Repeatable
Observable
Generally Unchanging
If there is an equation – it’s probably a law
Scientific Theories EXPLAIN why or how a law works
Based on many verified experiments
Broad use of many hypotheses summarized into one theory
Always TESTABLE, but never proven
More likely to change than a law
Changed to a “better” explanation
Updated to include new test results
Sometimes completely refuted and replaced with a new theory

4. Scientific Inquiry – Scientific Methods & Experimental Design
Scientific Methods are systematic approaches to answering questions or solving problems
Uses Observation and Guess and Check to rule out “wrong answers” and find “right answers”
Generally, tests one variable at a time
Draws conclusions based on observations (EVIDENCE BASED CONCLUSIONS)
Science is done in Community
Share results
Share experimental procedures
Debate different theories

5. Scientific Inquiry – Scientific Methods & Experimental Design
Independent Variable
The “tested” variable
Manipulated by Experimenter
Graphed on the Horizontal Axis
Dependent Variable
The responding variable
Is OBSERVED by the Experimenter
Graphed on the Vertical Axis

6. Scientific Inquiry – Scientific Methods & Experimental Design

7. Scientific Inquiry – Scientific Methods & Experimental Design
Scientific Method & Experimental Design
Constants
Factors that are NOT changed during an experiment
Keeping constants unchanging ensures that the I.V. is the only factor being tested
Control (Group)
An “untested” group used for comparison
Minimize the “involvement” of the I.V.
Hypothesis
An educated guess about the outcome of an experiment
TESTABLE
Focuses on the question or problem
If I.V. “changes,” then the D.V. “responds”
Conclusion
State if hypothesis was supported or not supported
Discuss Sources of Error and “Confidence” in Results
Suggest Other, Related Experiments, or Alternative Hypotheses

8. Scientific Inquiry – Fields of Science
Types of Science
Earth Science
Geology
Astronomy
Life Science
Biology
Ecology
Environmental Science
Physical Science
Chemistry
Physics
Technology vs. Science
“Pure” Science
Studies Natural Phenomena
Develops Laws & Theories
Generally Big Picture
Often Slow
Technology
Application of Science
Solve Problems
Improves Processes
Makes life easier

9. Scientific Inquiry - Measurement
Measurement is making observations to collect quantitative data by comparing observed values with standard values
All measures include:
Numbers
Units of measure
Uncertainty
When making scientific measurements the last digit in a measurement is the estimated digit
The estimated digit is one place value smaller than smallest division of the measurement instrument
All digits recorded are significant digits

10. Scientific Inquiry - Measurement
Measurement – Accuracy vs. Precision
Accuracy in measurement means measured values are close to the actual value Correctness in Measurement
Precision in measurement means measured values are close to each other Repeatability in Measurement

11. Scientific Inquiry – Dimensional Analysis & Unit Conversions
Units of Measure & Unit Conversion
Units “describe” the property being measured
Mass
Mass is a measure of “how much matter is present”
Measured in
Grams (g)
Pounds (lb)
Volume
Volume is a measure of “how much space is being taken up”
Cubic Meters (m3) [ length x width x height ]
Liters (L)
Cubic feet (ft3)
Gallons (gal)

12. Scientific Inquiry – Dimensional Analysis & Unit Conversions
Units can be converted using “factors” that change the mathematical presentation, but not the actual value of the property
Conversion factors are based on equalities between different units
For example
1000 m = 1 km
1mL = L
12 inches = 1 ft
2.54 cm = 1 inch
Half of the units of the conversion factor “match” and will cancel with the units being converted
Half of the units of the conversion factor are the “new” units

13. Scientific Inquiry - Measurement
Unit Conversions
Match the given units in the “reciprocal” position (on the diagnol)
Put “wanted” units opposite “matched” unit
Cancel matched unit
Repeat 1 – 3 until “desired” unit is achieved
Multiply or divide as necessary
Re-write with new units and new mathematical value

14. Scientific Inquiry - Measurement
Scientific Notation
All ordinary notation numbers can be written as scientific notation numbers
Coefficient x 10Exp
Coefficient should be greater than or equal to 1 but less than ten.
Small numbers (numbers less than 1) use negative exponents
Large numbers (numbers greater than 10) use positive exponents

15. Scientific Inquiry – Measurement
Significant Digits
‘Certain’ digits and one ‘estimated’ digit in a measure or calculated result
A system of rounding that is used to maintain and present the precision of measure throughout calculations using measured values.
Counting Significant Digits
All non-zero digits in a measure are significant digits
Entrained zeros (zeros between non-zero digits) are significant digits
Leading zeros are NOT significant digits
Trailing zeros in a value are significant IF there is a decimal point present in the value.

16. Scientific Inquiry – Measurement
Adding and Subtracting with Significant Digits
Calculate answer ‘normally’
Round answer to the smallest shared place-value of all inputs in the calculation
Multiplying and Dividing with Significant Digits
Round answer to the fewest number of sig digs present in all inputs in the calculation