Monday, September 16, 2013

Different periodic table of elements

I found some that actually make sense.

These ones are all the electron configurations






This one just shows which group of elements have a tendency to lose or gain  electrons


Sunday, September 15, 2013

A very good website for chem!

I found a really helpful website that might help you guys! Since I don't update as fast, this guy is more helpful.
http://www.thattutorguy.com/chemistry-general/

Monday, September 9, 2013

Calculating Molarity.

So let's say  there was question like:
A 200 mL solution contains 3.98 g of glucose (C6 H12 O6). What is the molarity of this solution?
The first step is to find the molar mass/ molecular weight. 

Carbon:  6 x 12.0107=72.0642
Hydrogen :12* 1.00794=12.09528
Oxygen 6*15.994= 95.664

Now add them all up, you should get: 
179.82 grams/mole.
 What you have to do know is look at equation again, it says A 200 mL solution contains 3.98 g of glucose, which means the solute  is glucose. how much glucose? 3.98 grams of glucose!
so 3.98 is divided by molar mass

The answer is: 0.022 moles (CH12 O6).

You need to know the conversion factor.
 1 L/ 1000 mL
You would have to divide  200 mL with 1000 mL.
 it would  be  0.2 liters
now  just divide  0.022 moles/ 0.2 liters = 0.11 M (molarity) 

You would do the same thing molality except it is looking at the solvent and converting grams to kilograms. 

Thursday, August 29, 2013

How to calculate Percent by Mass.

For this particular set of questions, you have to know what  solute and solvent are. Solute is the mixture or the thing that mixes. Solvent is the thing the solute mixed in. So let's say  I had sugar and water. Sugar would be the solute because it mixes it with the water (solvent).

Now that we have that cleared. we have to memorize a little thingy.

It is   mass of solute/mass of solution times 100.

Okay.
So they gave us a problem that looks like this:
What is the percent by mass of  CO2 in a solution containing 13 g  CO2 dissolved in 400 mL of water.

Look at the problem again. If you read this carefully you can see that dissolved is in bold. Now what dissolved in the water? The 13 grams of CO2!!!

That means the solute is 13 and the solvent is water.
Now we add the solute and the solvent.
13+ 400= 413g.

Now we know the mass of solution.
Look at the eqaution above.
mass of solute/mass of solution times 100.

Just plug in the numbers.
13/413 times 100= 3.14%

 So the answer for this equation is 3.14 %.

Any other questions, please comment!



How to find the Formula Unit.

Let's say some one asked,
 74.5 grams of H2O, please find the formula unit.

To find the formula unit first we sort of do the same thing like when we find the Molar Mass.
So Hydrogen has 2 atoms,  and Oxygen has 1 atom.
Multiply The hydrogen atom  with the atomic mass and  do the same thing for Oxygen.

You would have:
H: 2 x1.0079= 2.0158
O: 1 x16= 16

Now add them
You should have 18.0158.

Then get the 74.5 and divide it by  18.0158.
 The answer is 4.1325

Finally the last step is multiplying the answer by Avogadro's Number ( 6.02 x 10^23).

You should get

24.88 x 10^23 formula units H2O.

I think you can figure this out easily.

Hope this helps

Any other questions?

Any more questions you guys have or requests of explanations, Please comment below.
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