Chemistry – Ch 2 Units & measurements

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

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.

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

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

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

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

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

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

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

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

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!