SI System and Percent Errors

 SI System prefixes:

 -We can put a prefix in front of a unit and change the power of the unit.

 -The SI System uses many prefixes to represent very large or very small numbers

 -A common mistake is to uses scientific notation and prefixes together, they will becomes very confusing (Ex. 2.5x 10^7nm)

Experimental Accuracy:

   -In general the maximum accuracy of any measurements is ½ of the smallest division of the measuring device.

   -A ruler with measurement of millimeters has a maximum accuracy of (-, + 0.5mm)

Examples:

A gradulated cylinder has unitsa of 1.0ml. The Accuracy of the cylinder is 0.5ml. The liquid  in a gradulated cylinder will typically form a curved top called a  "Meniscus". The volume is taken at the bottom of the Meniscus. Sometime the Meniscus will curve upward, if so then just measure the peak of the Meniscus.

Expressing Error:

-Error is a fundamental  part of science. There are usually 3 reasons for an error:

  1) Physical error in the measuring device

  2) Sloppy Measuring

  3) Changing ambient conditions

Calculated Error:

-2 different types of error: 

 1) Absolute Error

 2) Percentage Error

(Absolute Error = Measured - Accepted)

Percent Error:

-It is the most common. An equation would look like:

(Percent Error = Absolute Error / Accepted Value)

                               or

% Error = {Measured - Accepted / Accepted} x 100

Classification Of Chemicals!!!

Classification of matter:

Understanding matter begins with how we name it. We can divide matter into 2 types:

A)    Homogenous Substances:

-Homogenous consists of only one visible component (Ex.                  Distilled Water, Oxygen, Graphite)

B)   Heterogeneous Substances:

 -Heterogeneous contains more than one visible component (Ex. Chocolate Chip Cookies)

C) Pure Substances

  -Elements are substances that cannot be broken down into a simpler substance by a chemical reaction

  -Compounds are substances that are made up of 2 or more elements and can be changed into elements or other compounds by a chemical reaction (Ex. Salt Water)

 D) Solutions:

- A solutions is a homogeneous mixture of 2 or more substances

-Solutions usually involve liquids but don’t have to. (Ex. Fog and Steel)

· The compound that is the most present is the solvent.

· Water is the most common solvent.

· The compound present in smaller amount is the solute.

Ways of separating:

1.   Hand

2.   Filtration

3.   Distillation

4.   Crystallization

5.   Chromatography

5.   Chromatography

CHEMISTRY!!!

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