# Basic Chemistry

Essay by 24 • November 10, 2010 • 998 Words (4 Pages) • 1,811 Views

**Page 1 of 4**

Observing- use of senses to obtain information

-Making measurements and collecting data

-Qualitative-descriptive (ex: color)

-Quantative-numerical (ex: mass)

-System-a specific portion of matter in a given region of space that has been selected for study during an experimentation or observation

Hypothesis- testable statement

-Formed from generalizations about data

-Basis for making predictions

-"If-then" statements: "then" is the prediction that is the casis for testing using an experiment

Theorizing-when data shows a hypothesis is correct you try to explain it by constructing a model

-Model- more than a physical object; it's often an explanation of how phenomena occur and how data or events are related. May be visual, verbal, or mathematical

-If a model explains a phenomena correctly, may become part of a theory

-Theory-broad generalization that explains a body of facts or phenomena

-Theories are successful if they can predict the results of new experiments

Units of measurements- measurements are quantitative, represent quantities

-Quantity- something that has magnitude, sizes, or amounts

-Units of measurement compare what is to be measured with a previously defined size

SI measurment-adopted in 1960

-Has seven base units, most other units are adopted from these seven

-Defined in terms of standards in measurement. Standards are objects or natural phenomena that are of constant value, easy to preserve and reproduce, and practical in size

-International organizations oniter the defining process

-Everything must agreed upon internationally

Seven basic units: Length (l), mass (m), time (t), tempature (T), amount of substance (n), electric current (I), and luminous intensity (Iv)

-Mass-measure of the quantity of measure-standard unit: kilogram

-Weight-measure of the gravitational pull on matter

-Length-standard unit: meter

-Time-standard unit: second

-Tempature-standard unit: kelvin

-Amount of substance-standard unit: mole

-Electric current-standard unit: ampere

-Luminous intensity-standard unit: candela

Derived units- combinations of SI base units

-produced by multiplying or dividing standard units

Some derived units: Area (A), volume (V), density (D), molar mass (m), concentration(c), molar volume (Vm), energy (E)

-Volume-amount of space occupied by an object

-Standard unit: cubic meter

-Density-ratio of mass to volume, or mass divided by volume

-Standard unit: kilogram per cubic meter

-A chacteristic physical property of a substance

Conversion factor-ratio derived from the equality between two different units that can be used to convert from one unit to the other

-Conversion factors always equal 1

-Can derive conversion factors only if you know the relationship between the unit you have and the unit you want

Using scientific measurements- for a reported measurement to be usedful, there must be sime indication of its reliability

or uncertainty

-Accuracy-refers to the closeness of measurements to the correct or accepted value of the quantity measured

-Precision-refers to the closeness of a set of measurements of the same quantity made in the same way

-Percent error-calculated to find out if the accuracy of an individual value or of an average experimental value can be compared quantatively with the correct or accepted value

-Calculated by subtracting the experimental value from the accepted value, dividing the difference by the accepted value, then multiplying by 100

-Positive value if a. value is > than e. value

-Negative value if a. value is < than e. value

-Uncertainty or error always exists

-The skill of the measurer limits the reliablty of results, as do the insturments he uses

-Significant figures- (in a measurement) consists of all the digits known with certainty plus one final digit, which is somewhat uncertain or is estimated

-Insignificant digits are never reported

-If a number contains no zeros, then all digits are significant

-Rules for determining significant zeros:

1.zeros appearing between nonzero digits

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