Units of Measurement and Uncertainty in Measurement

Prefixes Used with SI Units

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

- tera: 10^12                                    - femto: 10^-15

- giga: 10^9                                      - pico: 10^-12

- mega: 10^6                                   - nano: 10^-9

- kilo: 10^3                                     - micro:10^-6

- hecto: 10^2                                   - milli: 10^-3

- deca : 10^1                                   - centi: 10^-2

SI Prefixes

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

Experimental Accuracy 

In general the maximum accuracy of any measurement is one half of the smallest division of the measuring device.A ruler with measurements of the millimeters has a maximum accuracy of positive or negative 0.5mm

Expressing Error 

Error is a fundamental part of science

There are usually 3 reasons for error: 

                     > physical errors in the measuring device 

                     > "sloppy" measurements

                     > changing ambient conditions 

Calculating Errors  

Two different possibilities: Absolute Error, Percentage Error 

Absolute Error

  

Measured value minus accepted value  

Absolute Error = Measured - Accepted 

Percent Error  

Most common 

Percent error = Absolute error/Accepted value 


-Benedict Suratos

Classification of Chemicals

How Can We Classify Matter?

There are two distinct types of matter used for classification: homogeneous substance and heterogeneous substances. 

• A homogeneous substance consists of only ONE visible component 
• A heterogeneous substance consists of MORE THAN ONE visible component.  

The following chart provides a clear idea of where a substance would be classified. Keep in mind, figuring out whether a substance is homogeneous or heterogeneous is typically a simple matter of what the naked eye can distinguish. 

What is a Pure Substance? 

Similar to matter, there are two types of pure substances: Elements and Compounds. 

• Elements are substances that CANNOT be broken down into simpler substances by chemical reactions. 
• Compounds are substances that are made up of TWO OR MORE elements and can be changed into elements (or other compounds) by chemical reactions. 

Unlike matter, it is difficult to discern if something is a element or a compound as the differences are only "visible" on the atomic level.  

What is a Solution? 

A solution is a homogeneous mixture of two or more substances. More often than not, solutions come in the form of liquids but there are exceptions such as steel and fog. In a solution, there exists two key components: 

• The Solvent: The compound present in the greater amount. Water is the most common solvent.
• The Solute: The compound present in the lesser amount. 

Click here for an elaboration on this broad concept.

What Are Mixtures and How Are They Separated? 

Many mixtures are easy to identify but others can be easily confused as pure substances.  There are two types of mixtures: homogeneous mixtures and heterogeneous mixtures. 

• In homogenous mixtures, the different parts are not visible. 
• In heterogeneous mixtures, the different parts are visible.      

There are many methods and scientific procedures devised to separate mixtures and you would select one depending on which mixture you are working with:  

• By hand (Homogeneous and Heterogeneous mixtures) 
• Filtration (Heterogeneous mixtures only - Most commonly used method)  
• Distillation (Heterogeneous mixtures only)
• Crystallization (Heterogeneous mixtures only)
• Chromatography (Heterogeneous mixtures only) 

For more information, along with examples, regarding mixtures click here. 

-Simon Sierra

The Times They Are a-Changin'

What is a Chemical Change?

A chemical change occurs when a substance undergoes a chemical reaction and produces a new substance. Signs of a chemical reaction include color change, production of heat or light, gas production, odor, or sound.

Examples include iron rusting, cooking an egg, burning wood, or photosynthesis. Chemical changes often release energy also known as being exothermic.

What is a Physical Change? 

A Physical change affects the size, shape, color or matter of a substance but does not affect its composition. The starting and ending materials of a physical change are the same even though they may appear different. Examples include melting an ice cube, boiling water, and breaking glass. Physical changes are endothermic meaning they absorb energy.

Come gather round people wherever you roam and test your knowledge on differentiating the two types of changes while listening to some Bob Dylan.

QUIZ

http://www.teacherbridge.org/public/bhs/teachers/Dana/chemphys.html

MUSIC

http://www.zappinternet.com/video/ViMsTofFek/Bob-Dylan-The-Times-they-are-A-changin-1965

Thanks for a-tunin' in! 

-George Spencer

Bringing Balance To the Force... And Equations

What are phase symbols?

Phase symbols are subscripts that indicate the phase of the chemical.


    Ex. Al(s) - Solid      H20(l) - Liquid     H2(g) - Gas     AgNO3(aq)Aqueous


Chemical equations from word equations


Solution means something dissolved in water and therefore is an aqueous phase.

1.     Chemical equations must include phase symbols and a balance of the equation.
2.     Diatomic molecules : H2, N2, O2, F2, Cl2, Br2, I2
3.     Polyatomic molecules : P4, S8

Examples:


1) A solution of barium phosphate is mixed with aqueous sodium sulphate to yield solid barium sulphate and aqueous sodium phosphate.


Ba3(PO4)2 (aq) + 3Na2SO4 (aq)   =>  3BaSO4 (s) + 2Na3PO4 (aq)


2) A solution for aluminum chloride, carbon dioxide, and water can be prepared mixing pure aluminum carbonate with a solution of hydrochloric acid.

Al2(CO3)3 (s) + 6 HCI (aq)  =>  2 AlCI3 (aq) + 3 CO2 (g) + 3 H2O 


If you seek balancing beyond chemical equations young Jedi, perhaps it is time for you seek out the force.

There's no better teacher than Ol' Ben Kenobi 

When you are your done doing that, try honing your skills on the beautiful planet of Alderaan. Oh wait... Just go to the Dagobah system.

-Benedict Suratos

Watch Out Doktor Jones!

You should always read the procedure first. This and many other similar rules will ensure your safety whether your lurking in deep, abandoned Peruvian Temples or in science labs. Common sense can do you good but not understanding basic safety locations or how to properly use lab equipment is a hazard in itself. 

Analyzing any noticeable dangers and the precautions you must take to work around them is advised; this is why you must always be under adult supervision, in case you miss anything. In a chemistry lab, there is always the possibility you might be working alongside open flame and/or corrosive chemicals. With such risks the best tool to be equipped with is responsibility. Not all of us can get out of sticky situations like the Professor.  

Boulders might crush you, but burns will last forever. Here's a few tip's on how to avoid them:

http://www.sanbenito.k12.tx.us/teachers/science_safety/Safety_And_Lab_Rules.html

-Simon Sierra

Chemistry, AWESOME!

Welcome to our blog! We are three cool dudes that have been brought together for the greater good of all chemistry, combining the minds of  Ben, George and Simon. CHEMISTRY TIME!

Artwork by George Spencer