Empirical formulas and Molecular formulas

Empirical formula: it gives the lowest term ratio of atoms (or moles) in the formula. *All ionic compounds are empirical formulas*

Ex: C3H6 (propene) ---> molecular formula
     CH2 ----> empirical formula


Molecular formula: it is a multiple of the empirical formula and shows the actual number of atoms that combine to form a molecule

Ex. A molecule has an empirical formula of C4H10 and a molar mass of 29 g/mol, what is the molecular formula
Ans: C2H5

More Mole Conversion(2)

Today we are going to teach you to solve Two Step Mole Calculartion Problems~

If we were asked to convert 22 grams of copper to atoms of copper, we'd have to go from one end of the map to the other. Instead of doing a simple one step calculation, we'd need to do a two-step calculation, with the first step going from grams to moles and the second step going from moles to atoms.

How can we solve this kind of problem? Well, we start off by doing the same thing that we did in our last example: We had to convert grams to moles before, and we can see from the map that we have to convert grams to moles now, too. To refresh your memory, here's the calculation from last time:

In the next step, we do the same thing over again, except that we need to add another T to the T-chart. When you do this, take the units of the thing at the new top left and put them on the bottom right (in this case, moles). Then take the units of what you want (in this case, atoms) and put it in the top right. Finally, put in your conversion factors, which from the chart above is Avogadro's number, or 6.02E23. Since this number refers to the number of atoms in a mole of a substance, we put this in front of "atoms of copper". Again, put the number "1" in front of moles, because we're saying that there are 6.02E23 atoms in ONE mole of an element.
When we add all these terms in, we can cross out the units that cancel out, as shown. To get the answer, multiply all the numbers on the top together and divide by the numbers on the bottom. Your answer should then be set up like this:

And that's how you do mole problems!

More Mole Conversions

   So today we did more mole conversions, it involves more than one step, for example,

What is the mass of 2.78 X 10 ^22 Fe atoms:  2.78 X 10^22 / 6.022 X 10^23 X 55.8 = 2.58 g

Moles

So last class we learned about moles, and more masses. We also learned about Avogadro's hypothesis, he said if there're equal volume of different gases at the same temperature and pressure have the same number of particles. We also learned about different masses, formula mass, molecular mass and molar mass.

The last thing we learned about is Avogadro's number, the number of particles in 1 mole of any amount of substance.

6.022 x 10 ^23 particles/mole


I also found this interesting song about mole----http://www.youtube.com/watch?v=8vaaRPBXHgM

Graphing

It's always easy to graph a picture by using computer, so that we can use Excel to record all the data and graph those data immediately and correctly.

1)First of all, we have to set up two different objects that we want to graph, one for X-intercept and the other for Y-intercept
2)Record the data you have
3)Select all the data and click SCATTER from chosing the graphing style
4)Decorate your table! (try as much change as you can :)

LAB 2E

So by doing today's lab we got deeper into mass, volume and density. We did the lab by using aluminum foils, find out their density and measurements and we also did some questions that are related to the measurements.
So this link below can explain more about density

http://www.youtube.com/watch?v=Q4EBOE4pJyw

Accuracy & Precision

Accuracy : how close the measurement comes to the accepted/real value

Precision : how reproducible a measurement is compared to similar measurements

No measurement is exact. Its just a estimation. It may still has some degree of uncertainty

~Absolute uncertainty = largest difference between the average and the lowest/highest measurement

Method 1 : Calculate the average(at least 3)

For example : 8.3, 8.5 & 8.1

Average = 8.3
Absolute uncertainty = 8.5 - 8.3 = 0.2
It will recorded as 8.3+/-  0.2

Method 2 : Determine the uncertainty

Measure the best precision that you can. You should estimate to a fraction 0.1 of the smallest segment on the instrument scale.

For example :
Thermometer  Smallest : 1degree,   Best precision : 0.1degree,   uncertainty+/- : 0.1degree

~Relative Uncertainty = Absolute uncertainty/Estimated measurement