Percent Composition

 What is percent composition? Well... it is a compound that is a relative measure of the mass, of the different elements that are in the compound. Anyways...you need to be able to figure out the molar mass of each element, so if you are not sure what the molar mass of elements are, please read the previous blogs!!

This is an example of what a element would consist of, if the percent composition was represented by a pie graph

Now... how to actually calculate the percent composition of an element...

Ex 1/ What is the percentage composition of H20

First... you need to find:
Total Molar Mass of H2O.= 18.0g
Molar Mass H = 2.0g/ mol
Molar Mass O = 16.0/ mol

After that you find the % of each element, by dividing it by the total molar mass.

% of H = 2.0g per mol/ 18.0grams x100 = 11.1%
% of O = 16.0 per mol/ 18.0 grams x 100 = 88.9%

11.1%+88.9%= 100%

* Because there were no numbers in the questions, then you don't have to count the significant figures, so just round the number by one decimal place

Ex 2/ What is the percentage composition of Sc2(SO4)3

Total Molar Mass: 333.3 grams
Molar Mass Sc: 45.0 g/mol
Molar Mass S: 96.3 g/mol
Molar Mass O: 192.0 g/mol

% of Sc = 45.0 grams per mol / 333.3 grams x100 = 13.5%
% of S = 96.3 grams per mol / 333.3 grams x 100 = 28.9%
% of O = 192.0 grams per mol / 333.3 grams x 100 = 57.6%

The total percentage totals up to 100%

Ex 3/ What is the percentage composition of Zn(ClO3)2

Total Molar Mass: 232.4 grams
Molar Mass Zn: 65.4 grams/mol
Molar Mass Cl: 71.0 grams/mol
Molar Mass O: 96.0 grams/mol

% of Zn: 65.4 grams per mol / 232.4grams x100 = 28.1%
% of Cl: 71.0 grams per mol / 232.4 grams x100 = 30.6%
% of O: 96.0 grams per mol / 232.4 grams x 100 = 41.3%

The total adds up to 100% YAY!

Ex 4/ If a compound contains 48.0 grams of C, 6.0 grams of H, 64.0 grams of O, and contains some amount of Be and has a total mass of 127.0 grams. Calculate the % composition.

127.0-48.0-6.0-64.0 = 9.0 grams

% of C: 48.0 g per mol / 127.0 grams x 100 = 37.8%
% of H: 6.0 g per mol / 127.0 grams x 100 = 4.7%
% of O: 64.0 g per mol / 127.0 grams x 100 = 50.4%
% of Be: 9.0 g per mol / 127.0 grams x 100 = 7.1%

*Remember, there are numbers in the question, so sig figs count!

FINALLY......

Ex 5/ If a compound contains 137.3 g of Ba, 28.0 g of N, and contains some amount of O and has a total mass of 261.3 grams. Calculate the percent composition.

261.3 - 137.3 - 28.0 = 96.0 grams

% of Ba: 137.3 g per mol/ 261.3 x 100= 52.5%
% of N: 28.0 g per mol / 261.3 x 100 = 10.7%
% of O: 96.0g per mol / 261.3 x 100 = 36.7%

In the case the percentages only add up to 99.9%. Due to the rounding, there may be some cases where the percentages do not add up to 100%. If it is only 0.1% off, it is not a big deal, but to be safe ask Ms. Chen =]

These video's can maybe explain in more detail on how to calculate percent compositions..






After having all that knowledge inputted into your brain... time to use those skills on some other problems!

http://misterguch.brinkster.net/PRA023.pdf
http://cmsweb1.loudoun.k12.va.us/52820831134912597/lib/52820831134912597/Moles/Homework/masspercomp.pdf



Good Luck...

November 25, 2010 (QUIZ DAY)

Whatup? Today we took the mole conversions quiz. Ms.Chen as well as half our class wasn't present today, probably because of the snow storm that hit Vancouver overnight. Anyways, the substitute teacher corrected the mole conversions review in the begining of the class. He then gave us 10 minutes to study. After studying we had the rest of the class to complete the test. I hope everyone did well. See you guys later.




PH

Converting from Particles to Mass and Mass to Particles

So now that we understand how to convert from grams to moles, moles to grams, particles to moles and moles to particles, let's try converting from particles to grams and grams to particles.

These are now 2 step conversions. Once again we need our periodic table.

Let's start with particles to mass.

If you have 2.78 x 10^22 Fe atoms, how many grams are there?
First, you want to get rid of the atoms, so let's go from atoms to moles.

2.78 x 10^22 atoms of Fe x 1 mole / 6.022 x 10^23 atoms

Now, we also know how to go from moles to grams, so let's get rid of moles.

2.78 x 10^22 atoms of Fe x 1 mole / 6.022 x 10^23 atoms x 55.8g (molar mass of Fe) / 1 mole

Now our final answer is going to be (2.78 x 10^22)(55.8g) / (6.022 x 10^23) in 3 sig figs.
So, we get 2.58g. This means 2.78 x 10^22 Fe atoms weighs 2.58 g.

Now mass to particles...How many atoms of Fe are in 20.0g of Fe?
So, we get rid of grams by multiplying moles/grams.

20.0g of Fe x 1 mole / 55.8g (molar mass of Fe)

Then, since we want particles, we get rid of moles by multiplying particles/moles.

20.0g of Fe x 1 mole / 55.8g (molar mass of Fe) x 6.022 x 10^23 atoms / 1 mole
Our final answer of 20.0g Fe in particles (3 sig figs) is 2.16 x 10^23 atoms.

Video time :)

More on Moles...

Well... I'm going to start off with a funny story... My friend VIVIAN CHENG thought the "moles" were the black dots that grow on your face... then she thought it was the ANIMAL mole..... until i explained to her...

Well...we're still learning about moles, and how to convert moles... as much as I dislike moles, we still gotta learn about MOLES!...
Keep in mind Avogadro's Number  is 6.022 x 10^23 --> particles/mole

Molar Mass

You can convert molar masses from either:

1. Particles to moles
or
2. Moles to particles

Converting molar masses is somewhat simple. It is just like doing unit conversions.

For example:
1) Convert 4.5 x 10^24 particles to moles
4.5 x 10^24 particles x 1 moles/6.022 x 10^23 particles = 7.5 moles




What I did, was I divided 4.5 x 10^24 by 6.022 x 10^23. The particles cancel out. And because there is only one mole, the answer is simply 7.5 moles.

*Remember that you have to count to the correct number of significant digits.

2) *(2 atoms) Convert 0.82 moles CO₂ to molecules

0.82 moles x 6.022 x 10^23 particles/ 1 moles =   4.9 x 10^23 molecules CO₂

The moles cancel out, so you simply multiply 0.82 x (6.022 x 10^23) particles . Because its  4.9 x 10^23/ 1, it works out to just be 4.9 x 10^23 molecules CO₂

There are two atoms, so there is one more step involved. Well...it's not anything special... but...here goes!

4.9 x 10^23 molecules  CO₂  x 2 atoms O/ 1 molecule CO2  = 9.8 x 10^23 atoms of Oxygen 

And again... the molecules cancel out, and you just multiply the numbers. 

This video may help explain some questions you  may have: 

Are you tired of converting moles yet? Well we're almost done, so bear with me!
Now.. we are going to learn how to convert moles to grams, and grams to moles. Get your periodic table for this!!! We need it !!  To find the molar mass of an element, look for the atomic mass of the element!

Example:

1) Convert  3.06 moles Fluorine to grams
The molar mass of Fluorine is 19.0g/mol

3.06 moles x 19.0g/1 mole = 58.1 grams of F

Here, the moles cancel out, and you just multiply 3.06 x 58.1 grams of F...and.. BAM, you get the answer!


2) To convert 7.65 grams of Fluoride to moles
The molar mass of Fluorine is 19.0g/mol

7.65grams x 1 mole/ 19.0grams = 0.403 moles F

                                                                Remember this guys! 


Oh...my... I am Finally done :) ok... well now that my suffering is over... your turn to suffer!!!!
Here are some practice sites:
http://misterguch.brinkster.net/conversionsworksheets.html
http://www.sciencegeek.net/Chemistry/taters/Unit4GramMoleVolume.htm

This is another video to reinforce the idea of converting moles..




OK DONE! BYEBYE! =]

The Mole

So today, we learned about moles. No, not the round thing on the skin....the Chemistry mole.


But first, let's understand a hypothesis of a great Italian scientist named Avogadro.
He proposed that equal volumes of different gases at the same temperature and pressure will have the same number of particles.


Now, let's define Atomic Mass.
This is the mass of 1 atom of the element in the units amu. (atomic mass units)
For example, if you look at the atomic mass of an element on the periodic table, it will give you how much 1 atom of that element weighs..


So, let's take Carbon. Carbon's atomic mass is 12.0 amu. This means that every carbon atom weighs 12 atomic mass units.


Now formula mass. This means you add up all the masses of the atoms in the formula of an ionic compound.


So.... let's say we have NaCl.


Na is sodium, and the atomic mass is 23.0.
Cl is chlorine, and the atomic mass is 35.5.


So by simple addition: 23.0 + 35.5 = 58.5 amu. This means that NaCl weighs 58.5 atomic mass units.


Molecular Mass: All the atoms of a formula in a covalent compound are added in amu.


So: Carbon Dioxide is
 C + O₂
12.0 + 16.0X2
CO<sub>2 = 44.0 amu


Molar Mass is the atomic, molecular, or formula mass of any pure substance, and the unit is in grams per mole.</sub>
For example, 1 mole of oxygen is just its atomic mass (16.0 amu, but in a different unit, g/mol.)



So 1 mole of oxygen = 16.0 g/mol
1 mole of carbon = 12.0 g/mol


They both have the same number of particles. Hence, the molar atomic mass of an element is the mass of 1 mole of that element.
It's just a unit that helps us and scientists count atoms and molecules, without actually counting every single atom.
And what Avogadro found, was that the number of particles in 1 mole of any amount of substance is always 6.022 X 10^23 particles per mole.



Now here's a video if you're still somewhat confused.







And here's a website to summarize the different types of masses to calculate.
http://www.mpcfaculty.net/mark_bishop/molar_mass_conversion_factors_help.htm

More Graphing

Well, next class (November 15, a long way I know. It's because of the Remembrance Day holiday coming up) will be our Chapter 3 Chemistry Test.

This test will focus on Significant Digits, Scientific Notation, Uncertainty, Density, the lab, and some conversions and graphing we learned last time.

We reviewed the unit, and then we went to the computer lab to do more graphing.

Please refer to the previous post for instructions on how you can make your own graph! :)

Anyways, got to go study now!

Graphing Analysis

In this Chemistry class, we went to the computer lab and made graphs that demonstrated the relationship between volume in hot and cold water.

Today, we learned how to make these graphs using OpenOffice; however, most of you have Excel on your computer, so that's the alternative.

First, you want to open up Microsoft Excel.

Next, you want to plug in a table of values into the cells.
Let's begin on A1, and labelling it as X values.
Then, put down some numbers for X. At the end you should get:

X values            
1
2
3
4
5

In the column beside (so starting with B1), label it as Y values.
In B2, enter an equation that can relate X and Y.
This equation must start with "=" then A_  (whatever cell number your values start at, in this case A2) then an operation.

So, we could have something in cell B2 like.....   =A2+5
Once the equation is set, you should see the number 6. (because 1+5 = 6)
So:

X values    Y values
1                6
2
3
4
5

Now, click on the cell with the y value 6. There should be a small box in the bottom right hand corner. Drag that all the way down until it covers the last y value.

You should see all the numbers plugged in by now.

X values    Y values
1                6
2                7
3                8
4                9
5                10

Now, highlight all the values, and click on the bar graph/chart option in the toolbar.
This will pop out a menu. In this menu, choose the scatter plot, and click next. Then, customize it to your liking, and fill in the x-axis and y-axis information, as well as a title.

After you click finish, a graph should pop out.



To add a linear trend line, right-click a point on the graph and click Add Trendline. You can even show the equation, which will give you the slope of this line you just graphed. (in y=mx+b form)

Adding a trendline:




The finished graph before you customize (i.e. changing colours, fonts):


Format your graph by changing the colours, fonts, etc.

AND You have now created a nice graph that shows your data clearly and effectively.

Another useful tool that can be used to make graphs or many cool geometric things, or even just having fun on the computer, is the Geometer's Sketchpad, introduced to me by my math teacher. :)

For more help on making a graph:

Lab 2E: Measuring the Thickness of Aluminum Foil

Lab 2E occurred on November 3, 2010. In this class we used basic math formulas to calculate the thickness of aluminum foil pieces. These formulas are. V=L*W*H,  D=M/V, or V=M/D. Basically each group weighed each piece of aluminum foil. We were then given the density of each piece, which is 2.70g/cm^3. Our next step was to measure the length and width of the aluminum with our ruler. After that we would find the volume by dividing the mass by the density. Once we got the voulme, we divided it by the length and width to get the height (aka Thickness).

We also used a formula to calculate if there was any errors with our test results.

experimental error = estimated measurement - accepted value x 100%

                       accepted value

Well that wraps about everything up. This lab was fun and easy. It was fun because we didn't have to wear any goggles. LOL, jokes.

PH

Density

Density is a material that is specified as mass per unit volume, or weight per unit volume. Now.. why is density important? Well, density is applied to many chemicals that are being tested. It can find out the buoyancy of an object or fluid. To calculate density, there is a formula...and here it is..

 

Density = mass/volume                       

           OR  

Volume = mass/density 

           OR  

Mass = Density x Volume

*Once you memorize one of them, you can move them around as you would mathematically to calculate density, volume or mass.

now... make sure you REMEMBER THE FORMULAS OF DENSITY!!!

To represent density:

solids - g/cmᵌ

liquid - g/mL 

If there is 1cmᵌ of water = 1 mL

then the density of water = 1.0g/mL

                                      = 1000g/L

Ex. Calculate the density of a liquid which has a volume of 28mL and a mass of 26.4g

density = mass ÷ volume

density = 26.4 ÷ 28 = 0.94 g/mL

Unless the fluids are mixed together, fluids that are less dense float on fluids that are more dense.

The Cup of fluids on the left have different density`s and as you see, the fluid on the top ( the clear fluid) is the least dense, the fluid on the bottom (the pink fluid) is the most dense, the fluid in the middle (the blue fluid) has density that is between the clear and pink fluid. The cup of fluid on the right can be mixed together with other fluid.

 

ᵈobjects > ᵈliquid = sink

ᵈobjects < ᵈliquid =float

For more practice, go to this site: http://serc.carleton.edu/mathyouneed/densitysp.html

watch this video for more help: