# Intro to Chemistry

 Chemistry
 the science that deals with the materials of the universe and the changes that these materials undergo; the study of matter
 Scientific method
 Observation:  qualitative or quantitative (measurement involving a number) Hypothesis:  a possible explanation for the observation Experiment:  testing the hypothesis Theory – – – Law A law tells what happened; a theory (model) is our attempt to explain why it happens   Theory:  a set of tested hypotheses that gives an overall explanation of some part of nature; an interpretation   Law: a summary of observed (measurable) behavior
 Steps used to solve problems
 1.  recognize the problem and state it clearly making an observation
 Theory
 a set of tested hypotheses that gives an overall explanation of some part of nature   an observation is something that is witnessed and can be recorded.  A theory is an interpretation – a possible explanatino of why nature behaves in a particular way
 Law   Theory
 A law is a summary of observed behavior; whereas a theory is an explanation of behavior.   A law tells what happened; a theory (model) is our attempt to explain why it happened
 measurement =   quantitive observation
 must always consist of a number and a unit
 Scientific notation
 simply expresses a number as a product of a number between 1 and 10 and the appropriate power of 10.    93,000,000 = 9.3 x 10^7   the number of places the decimal point is moved determines the power of 10; the direction of the move determines whether the power of 10 is positive (left) or negative 9 (right)
 Unit
 part of a measurement that tells what scale or standard is being used to represent the results of the measurement
 fundamental SI units
 mass          kilogram           kg length          meter          m time          second          s temperature          kelvin          k
 fundamental SI unit of length
 1 m = 39.37 in   1 in = 2.54 cm
 volume – m     mass – kg
 the amount of three dimensional space occupied by a substance     the quantity of matter present in a object   1 L = 1000 mL   1 kg = 1000 g 0.001g = 1 mg
 Every measurement has some degree of uncertainty   The numbers recorded ina measurement (all the certain numbers plus the first uncertain number) are called significant figures
 rules for counting significant figures
 Non zero integers ALWAYS count as significant figures   Leading zeros are are zeros that precede all of the nonzero digits.  They NEVER count as significant; they simply indicate the position of the decimal point.   Captive zeros are zeros that fall between nonzero digits.  They  ALWAYS count as significant figures.    Trailing zeros are  zeros at the right end of the number;  They are only significant if the number is written with a decimal point.   Exact numbers NEVER LIMIT the number of significant figures in a calculation.
 rules for using significant figures in calculations
 For multiplication and division, the number of significant figures in the result is the same as that in the measurement with the smallest number of significant figures.  LIMITING   For addition and subtraction, the limiting term is the one with the smalles number of decimal places.
 Conversion factor   Equivalance statement   dimensional analysis
 a ratio of the two parts of the statement that relates to two units     1 in = 2.54 cm the respective numbers are different because they refer to different scales   Changing from one unit to another via conversion factors (based on the equivalance statements between the units)
 Temperature
 Freezing and boiling points (the difference is 100 on both scales)     Fahrenheit     32     212 Celsius            0     100 Kelvin           273    373   TK = TC + 273  TC = TK – 273   TF = 1.80 (TC) + 32 TC = TF – 32 / 1.80
 Density
 the amount of matter present in a given volume of substance   D = mass / volume  in g/mL or g/cm^3    the device used to test the density of a solution is a hydrometer
 Specific gravity
 the density of a liquid; the ratio of a given liquid to the density of H2O at 4C
 Matter
 the stuff of which the universe is composed; has two characteristics:  it has mass and occupies space   States of matter: SOLID – has fixed shape and volume LIQUID – has definit volume but takes shape of its container GAS – has no fixed volume or shape
 physical properties   chemical properties
 odor, color, volume, state (solid, liquid, gas), density, melting point, and boiling point   its ability to form new substances
 Electrolysis
 the decomposition of water by an electric current, a chemical proces
 physical change   chemical change
 involves a change in one or more physical properties, but no change in the fundamental components that make up the substance.  The most common physical changes are changes of state.   involves a change in the fundamental components of the substance; a given substance changes into a different substance or substances.  Chemical changes are called reactions:  silver tarnishes
 Elements   Compounds   Mixture   Pure substance
 a substance that cannot be broken down into other substances by chemical methods   a substance composed of a given combination of elements that can be broken down into those elements by chemical methods.  A compound always has the same composition.    something that has variable composition; can be separated into pure substances: elements and/or compounds    will always have the same composition; either elements or compounds
 homogeneous mixture / solution   heterogeneous mixture
 is the same throughout   contains regions that have different properties from those of other regions
 distillation   filtration
 the separation process; physical method with no chemical change     separates a liquid from a solid; physical method
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