Chem Class- September 30, 2009

Mr. Doktor checked our homework from last class today. He then went over a powerpoint on the Classification of Matter.

Here's a diagram I got from a Chemistry book on classifying matter:

As you can see, there are two types of pure substances: Homogenous and Heterogeneous.
Homogenous substances consist of only one visible component (Eg: distilled water, oxygen, graphite) and Heterogeneous substances contain more than one visible compent (Eg: chocolate chip cookie, granite).

You can also see in the above diagram that there are also two types of pure substances: Elements and Compounds.
Elements are substances that cannot be broken down into simpler substances by chemical reactions (Eg: oxygen, iron and magnesium)
Compounds are substances that are made up of two or more elements and can be changed into elements (or other compounds) by chemical reactions (Eg: water, sugar).
The differences between them are only visible at the atomic level

We also learned about Solutions.
A solution is a homogeneous mixture of 2 or more substances. The component present in the greater amount is the solvent and the component present in the smaller amount is the solute. The symbol (aq) is used when something is dissolved in water.

Finally, Mixtures:
Many mixtures are easy to identify, but others are easily confused as pure substances.
In Heterogenous mixtures the different parts are clearly visible (granite, sand, fog) and in Homogeneous mixtures the different parts are not visible (salt, water, air).
There are different methods to separate methods depending on the type of mixture. These include:

• By hand (Heterogeneous mixtures only)
• Filtration (Heterogeneous mixtures only)
• Distillation
• Crystalization
• Chromatography

The above are all physical changes.

Chem Class- September 28, 2009

Here we are now in Unit 2: Properties of Matter. Today in class, we took notes on matter and then watched a video (part of a MythBusters episode), trying to see how many chemical and phyiscal changes we could spot.
So just what is matter?

MATTER

- Anything that has mass and occupies space

- It can exist in many different states but the most common are: Solid,Liquid,Gas,Plasma,Aqueous,Amorphous

Solid: Holds one shape and has a definite volume
Liquid: Can change shape, but has a definite volume
Gas: Can change shape and colume
Aqueous: Something dissolved in water

In this picture, we see that solids have strong bonds, liquids have weak bonds, gases have no bonds and plasma involves ionization:

- Can undergo many changes: Physical, Chemical and Nuclear

 Physical Changes: Involves changing shape or state of matter and no new substances are formed
(Examples: Crushing, tearing, boiling water, cutting wood, smashing cars)
Changing from a solid to a gas can often be confused as a chemical change but remember that if that chemicals remain the same it is a chemical change.

Chemical Changes: Properties of matter change and new substances are formed
(Examples: Conductivity, acidity, colour, iron rusting, burning wood, digesting food)

So remember: Changes of state are considered phsical changes:

Also, during the melting process, chemicals usually follow this path:

New substances are formed in a chemical change:

One last point before we are through: In physical and chemical changes, matter is neither created or destroyed. This is known as: Conservation of Matter. The French chemist Antoine-Laurent Lavoisier is considered to have discovered this concept.

Chem Class- September 23, 2009

Today we had our very first chapter test. It included the very first things we learned up until this point. So, after reviewing a bit on the board, we proceeded with the writing of the test.

   The main topics were:

Lab Safety

Lab Equipment

Fundamental Units

Scientific Notation

The SI System

Significant figures

Error

And Dimensional Analyis

Chem Class- September 21, 2009

Today:
Mr. Doktor talked to us about our Unit Test. Ooooooooh scary!
If we had already completed the Lab, we were to work on our Lab write up as well as our review questions (In preparation for next class...Ah!). The people who either didn't finish their lab or didn't start their lab had the time to do that.

I'm sure you're probably wondering what the actual mass of salt is that can be dissolved in 200 mL of water. So, after everyone verified their results from the lab, Mr. Doktor told us just that: 11.5 g! We calculated the percent error by using this answer and the answer we were using. Remember how to calculate that?

Percent Error = (observed - theoretical/ theoretical) x 100.

I have to say, a lot of us were off by a lot!;)

Here's another youtube video. This one's on calculating percent error. One thing to note, however, is that they use the word 'actual' value. We learned in class that 'accepted' is probably the better word since there would still be error in the measurement.



Time to study now for that test!

Chem Class- September 17, 2009

Today in Chem Class, we did a few more examples of Dimensional Analysis.

Ex) Change 120 kg into mg

120 kg x 1000 g/ 1 kg =  120 000 g x 1000/ 1 mg = 120 000 000 mg
The higlighted units are being cancelled.

Ex) 7.25 L/s into mL/min

7.25 L/ 1 s x 60 s/ 1 min x 1000 mL/ 1 L = 435 000 mL/min
The higlighted units are being cancelled.

Ex) 174 kg/s into Mg/h

174 kg/ 1 s x 3600 s/ 1 h x 1000 g/ 1 kg x 1 Mg/ 1 000 000 g = 626.4 Mg/ h
The highlighted units are being cancelled.

After we finished the examples, we went into our lab groups to do an expreiment that involved table salt and water.

The problem for this experiment is: What is the maximum amount of Sodium Chloride (Table Salt) you can dissolve in 200 mL of water? To find out, you first have to weigh 50 g of Sodium Chloride. Then, add the sodium chloride to 10, 20, 30 and 40 mL of distilled water until it stops dissolving (the solution is saturated) and the first salt crystals being appearing on the bottom of a beaker. After that, measure the mass of salt remaining. Finally record all the data in a table and graph the results of Mass of Salt vs Volume of Water. We can't tell you the results yet, because not all of use have done the Lab yet.

In fact, because we have a large class, only half performed the experiment and the other half will be going next class. Those that did not do the Lab, worked on a Conversion Worksheet that will be due on Monday. When the class was over, Mr. D told us that we would be having a chapter test on Wednesday! So fast huh?! Well, we'd better study hard!

Chem Class- September 15, 2009

Unit 1 has begun! After having a brief summary of the safety rules in the Chemistry Laboratory, we've headed straight into measurement. This includes how to make accurate measurements and what factors affect measurement, the SI System of measurement, significant digits and scientific notation to communicate results, experimental error and applying dimensional analysis to chemistry problems.

Right. So, the most common system in use today is the SI System (abbreviated from the French le System internationale d'unites).

There are 7 Fundamental units:

1) kg (Kilogram-mass)

2) m (Metre-distance)

3) s (Second-time)

4) K (Kelvin- temperature)

5) mol (Mole-amount of substance)

6) A (Ampere-current)

7) cd (Candela-luminosity)

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This is very helpful when converting from one unit to another. Here's a table of SI prefixes and symbols I got off the web:

And now here's a cute Chemistry cartoon that deals with SI prefixes that I got from a Chemistry book:

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 We also learned about significant figures. They are measured or meaninful digits. Unless you are counting a small number of objects, it can be difficult to find the EXACT value of a property such as mass, time, volume or length. You may be quite precise, but not exact. The number of significant figures is equal to all the certain digits plus the first uncertain digit.

Things to note:
- Digits 1-9 are always significant
- If no decimal point is shown, any zeros at the end do not count
- Zeros are significant if they are to the right of a decimal

Examples:
365.249 -6 signifcant digits
150 - 2 significant digits
0.002 - 1 significant digit
2.010 - 4 significant digits

When you are multiplying or dividing numbers, round to the least number of significant figures.
When you are adding or subtracting numbers, round to the least number of decimal places.
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Next, we learned about experimental error. There are usually three reasons for error:
1) Physical errors in the measuring device
 2) 'Sloppy' measuring
 3) Changing ambient conditions
-Error is taken to be half the smallest division on your measuring device.

- There are two different possibilities of error (well, these are the two we learned for now anyways):

Absolute Error and Percent Error  (most common)

Here's how to calculate both:

Absolute Error = Measured value - Accepted Value (A postive number means you are over the accepted value and a negative number means you are under the accepted value)

Percent Error = Absolute error/ Accepted Value
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Finally, we ended off with Dimensional Analysis. This is the easiest way to change from one unit to another. We were instructed of the four basic steps.

1) Find a unit equality

2) Find the conversion factors

3) Apply the conversion factor

4) Cancel units

Yes! It's that easy!

If you need the extra help, have a look online. Youtube even has some step-by-step instructions on Dimensional Analysis. Here's one example:

Check it out.

The Beginning

So, here we are in Chemistry 11! Mr. Doktor, our teacher, wants us to reflect on what we're learning in class by writing this blog. These writings should also be a great resource for us whenever we need to study. So, be sure to check back with us every other day, and we'll give a detailed summary of what we've been learning. We're moving a step towards taking the MYSTERY out of CheMISTERY!