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