Unit 1 Chemistry & You

Chemistry – the study of the composition of matter (the stuff things are made of) and the changes that matter undergoes You undergo and perform chemical reactions (rxns) everyday (breathing, eating, cooking.) You benefit from the work of chemists everyday (plastic ballpoint pen, microwave oven, post-it notes, ice cream, etc.)

The Scientific Method Observation Hypothesis Experiment Theory Example: Flashlight

Theories vs. Laws Everyday use of: Scientific Definition of : Theory: abstract thought untested in practice; an assumption or guess1 Law: A rule established by authority, society or custom1 Scientific Definition of : Theory: inferred explanation of some aspect of the natural world. Theories do not become laws even with additional evidence [or time]; they explain laws. However, not all scientific laws have accompanying explanatory theories.2 Law: a general description about how some aspect of the natural world behaves under stated circumstance(s).3  often in equation form Explain – to offer reasons for Describe – to give a verbal account of

Measurement Qualitative: results in descriptions (Gray Cats) Quantitative: results in numerical form (23 Cats) SI System – International System that’s used to standardize quantities. Why is this important? There are 7 base units from which all other units are derived (made) Base units - meter and second Derived unit (of speed) - meter per second

Quantity it represents 7 Base Units Unit Name Unit Symbol Quantity it represents *Kilogram kg Mass *Meter m Length *Second s Time *Mole mol Count, quantity *Kelvin K Temperature Candela cd Luminous intensity Ampere A Electric current

Kilogram (kg) mass measure of the quantity of matter; amount of material in an object Never changes (Weight – force due to the pull of gravity on an object; mass times acceleration  it can change) Do you weigh more at the top of a mountain, or at sea-level?

Meter (m) length Second (s) time Line segment connecting two points Volume = derived  m3 (Liter (L) is metric unit) 1 L = 1 dm3 = 1000 cm3 = 1000 mL Second (s) time Interval between 2 occurrences

Kelvin (K) temperature Measure of the average kinetic energy of particles that make up a sample K = oC + 273.16

Uncertainty in Measurement Measurements are uncertain Measuring instruments are never completely flawless Measuring always involves some estimation Why is using a millimeter or centimeter stick to measure a ladybug better than using a meter stick? Accuracy: how close measurement is to true value depends on care in measuring Precision: how close several measurements are to the same value (reproducibility) depends on estimation and number of divisions on instrument

How would you describe the following sets of numbers? 68.6, 68.7, 68.9  Aim = 23 Precise but inaccurate 40.002, 40.001, 39.999  Aim = 40 Precise and accurate 2.4, 6.0, 7.0  Aim = 4 Imprecise and inaccurate 0.874, 0.87, 0.86699  Aim = 0.87 Imprecise but accurate

Scientific Notation Used to make math with very large or very small numbers easier Numbers in sci.not. look like: M x 10n  4.0 x 102 = 400 3.23 x 10-3 = 0.00323 where M is a number 1-9 and n is an integer that tells you how many places the decimal has been moved. If n is negative, the number is less than one. M is the coefficient, n is the exponent

Multiplying Numbers in Scientific Notation To Multiply: Multiply coefficients, add exponents (2.0 x 10^3) x (3.0 x 10 ^4) (2.0 x 3.0) x 10^3+4 6.0 x 10^7 13

Dividing Numbers in Scientific Notation To Divide: Divide coefficients, subtract exponents (8.0 x 10^5) / (4.0 x 10 ^2) (8.0/4.0) x10^5-2 2.0 x 10^3 14

Adding and Subtracting Numbers in Scientific Notation To Add or Subtract: 1. Must make exponents the same make # smaller OR move decimal to the left, exponent increases make # larger OR move decimal to the right, exponent decreases 2. Then add or subtract coefficient and exponent remains the same 15

Dimensional Analysis & Factor – Label Method Dimensional analysis is a technique used to convert between units cmm Factor –Label method is the use of conversion factors with their labels to reach a desired quantity when doing a calculation Ex. Conversion factor 1 min = 60 s 17.0 min (60 s/1 min) = 1020 s

Significant Digits/Figures Used to tell how accurate your measurements and calculations are Sig. figs. contain all the certain digits and 1 estimated digit of measurement. Not all zeros are significant ex. 101.02 0.00670 2050 10.0 0.0023 30,050 314 Atlantic – Pacific rule helps to identify sig.figs.: If a decimal is Present, count from the Pacific; If the decimal is Absent, count from the Atlantic A P

Rounding with Significant Figures Decide how many sig. figs. the answer should have, then round to that many digits counting from the left Sample problem 3-2 p. 59

Addition and Subtraction with Significant Figures Answer should be rounded to the same number of decimal places (not digits) as the measurement with the least number of decimal places Sample problem 3-3 p. 60

Multiplication and Division with Significant Figures Answer should be rounded to the same number of significant figures as the measurement with the least number of significant figures Sample problem 3-4 p. 61

Density Definition: The mass per unit volume of an object Equation:

Percent Error % error = measured value – accepted value x 100% Used to compare a measurement to its accepted value If answer is negative, data is lower than expected. If answer is positive, data is higher than expected.

Sources 1. American Heritage Dictionary 2. NSTA Position Statements: The Nature of Science 3.Teaching about Evolution and the Nature of Science