1. Chemistry – Ch 2
Units & measurements

2. Scientific Method
Definition: Logical approach to solving problems by observing and collecting data, formulating hypotheses, testing hypotheses, and formulating theories that are supported by data
Observation
Observe to obtain information by making measurements and collecting data
Data types are descriptive (qualitative) or numerical (quantitative)
Qualitative examples: blue liquid, long ruler, hot beaker
Quantitative examples: 100 mL liquid, 6 grams salt, 6 cm aluminum
Chemists experiment and study a system:
specific portion of matter in a given region of space that has been selected for study during an experiment

3. Scientific Method (continued)
Hypothesis
Testable statement based on observation/research; can be “if, then”
To test  experiment!
Variables:
Independent: what the experimenter changes “I change”
Dependent: changes based on the independent variable
Controls: anything that remains the same/constant
Results either support or refute the hypothesis (NOT PROVE OR DISPROVE!)
If the hypothesis is supported, a model is formed.  Explanation of how phenomena occur and how data/events are related
Models lead to theories.  Broad generalizations that explain bodies of facts or phenomena
Theories are successful if they can predict results of new experiments.

4. SECTION 1 REVIEW PROBLEMS
Complete on a separate sheet of paper and insert into notebook.
Check for a grade!

5. Units of Measurement
Measurements represent quantity  magnitude, size, amount
SI Measurements: Le Systeme International d’Unités decides the 7 standards for measurements
MASS vs. WEIGHT:
Mass – quantity of matter
Weight – related to gravitational pull on matter

6. Measurements (continued)
Derived units: combination of 7 original units by multiplying or dividing
Density units for our lab:
g/cm3
g/mL

7. Density Practice Problems
Complete in notes.
Check answers in class once completed.
GET HELP IF NECESSARY!!

8. KNOW THESE CONVERSIONS!!
Conversion Factors
Definition: ratio derived from equality between two different units that can be used to convert from one unit to another
Examples:
4 quarters = $1.00
¼ cup = 4 Tablespoons
1000 milliliters = 1 liter
KNOW THESE CONVERSIONS!!
Milli
1000 milliTHINGS = 1 THING
Centi
100 centi THINGS = 1 THING
Deci
10 deciTHINGS = 1 THING
Kilo
1000 THINGS = 1 kiloTHING

9. Dimensional Analysis
Definition: mathematical technique using units to solve problems involving measurements
Do conversion problems in class and check answers! GET HELP IF NEEDED!!

10. SECTION 2 REVIEW PROBLEMS
Complete on a separate sheet of paper and insert into notebook.
Check for a grade!

11. Using Scientific Measurements
Accuracy vs. Precision
Accuracy: closeness of measurements to correct or accepted value
Precision: Closeness of a set of measurements to each other

12. Percentage Error
Definition: Accuracy of an experimental value compared to an accepted/theoretical value
Formula:
% error = [(experimental value – accepted value)/(accepted value)] * 100
% error is negative (-) IF the accepted value is GREATER than the experimental value
% error is positive (+) IF the accepted value is LESS than the experimental value
Complete practice problems in class and check your work. GET HELP IF NEEDED!