Percent Composition

So what did we learn today? That's right! Percent Composition!!!

Percent Composition is the mass percentage of a element in a molecule. 

To calculate percent composition it's as easy as 1 2 3! There's no formula to memorize... you wanna know the secret to it? 

There's no secret! In fact you do it all the time to calculate the percent for your marks. But if you do insist a formula here it is: % Composition = mass of element      X 100%

                                                            mass of compound  

Now you know this not so  secret formula, let's try it out!

EX 1. Calculate % composition of C2H4O2

 Total MM = 60 g/mol (the mass of C2H4O2)

% of C = 24 g/mol X 100 = 40%

                60 g/mol

           

% of H = 4 g/mol X 100% = 6.7%

               60 g/mol

% of O = 32 g/mol X 100% = 53.3%

                60 g/mol

And that's it! It's that simple! Bet you can't wait to do more of these eh? Well, you're in luck here's a few more examples!

1) Calculate the % composition of FeO.

2) Calculate the % composition of H2O

3)Calculate the % composition of Co(NO3)2

4)What is the % composition of the underlined portion of this compound C8H9NO2

5) A compound has a mass of 51.2 g. It contains 20g of O, 19.2 g of S and a mystery amount of N. What is the % composition of N?

ANSWERS AND SOLUTIONS:

1) Total MM = 71.8 g/mol

% of Fe = 55.8 g/mol / 71.8 g/mol = 77.7%

% of O = 16 g/mol / 71.8g/mol = 22.3%

2) Total MM = 18 g/mol

% of H = 2g/mol / 18g/mol = 11.1%

% of O = 16.0g/mol / 18g/mol =88.9% 

3) Total MM = 156.9 g/mol

% of NO3 = 124 g/mol / 156.9g/mol = 79.0%

% of Co = 58.9g/mol / 156.9g/mol = 37.5%

4) Total MM = 151g/mol

% of C = 96g/mol / 151g/mol = 63.6%

% of H = 9g/mol / 151g/mol = 5.96%

% of N = 14.0g/mol / 151g/mol = 9.27%

% of O = 32g/mol / 151g/mol = 21.1%

5)51.2- 20-19.2= 12 g of N 

Total MM = 51.2 g/mol

% of N = 12g/mol / 51.2g/mol = 23.4%

"To mole or not to mole, this is the question"

On Thursday's class, we had a substitute. First, he gave us the answers to the mole conversion worksheet. Then, he gave us a couple of minutes to review before writing our mole conversions quiz. After the quiz, we worked on two mole worksheets until class ended.

So lets hear some jokes, shall we?

Q:What did Avogadro teach his students in math class?
A: MOLE-tiplication!

Q: What was Avogadro's favorite Indian tribe?
A: The MOLE-hawks

Q: Why did Avogadro stop going to the chiropractor on October 24th?
A: Cause he was only tense to the 23rd!

Q: How does Avogadro write to his friends?
A: By E-mole!

Q: Which tooth did Avogadro have pulled out?
A: One of his molars!

teehee.

Uh oh, the mole conversions are getting complex :O

As mole conversions get more and more complex, remember to draw a MOLE MAP!

This is a perfect example of a mind map to use.
To get from...
Grams to moles - multiply by 1mole/MMg (molar mass in grams)
Moles to molecules - multiply by 6.022 x 10^23/1mole
Molecules to particular kind of atoms in a particle (not present in this mind map) - multiply by number of the specific atom/1molecule

Particular kind of atoms in a particle to molecule - multiply by 1molecule/number of the specific atom
Molecules to moles - multiply by 1mole/6.022 x 10^23
Moles to grams - multiply by MMg/1mole 

http://www.fordhamprep.org/gcurran/sho/sho/convert/molews1.htm offers some extra practice!

Now a bit more on Mole and Avogadro!

FUN FACTS!
1)6.022 x 10^23 Watermelon Seeds would be found inside a melon slightly larger than the moon!
2) Mole Day is an unofficial holiday celebrated among chemists in North America on October 23, between 6:02 AM and 6:02 PM.
3) There are 3 types of moles that live underground in North America: Eastern Mole, Hairy-Tailed Mole and Star-Nosed Mole.

DID YOU KNOW?

There is a lunar crater called Avogadro - named after this fine looking lad!

I'm watching you.

Moooooole Conversions!

Last time we learned about molar mass, so now it's time to use it in conversions. Remember: Avogrado's number = 6.022 x 10^23 particles/mol
Remember: Put answers in the correct number of sigfigs.

1) Converting between particles <--> moles. In this conversion, we use Avogrado's number.

    a) Particles --> moles
    # of particles x                1 mol               =  # of moles
                                 6.022x10^23particles

Ex.  If there are 3.01 x 10^24 C particles, how many moles are there?
              3.01 x 10^24 C particles x                 1 mol                   = 5.00 moles of C
                                                                6.022 x 10^23 particles
    b) Moles --> particles

Another example:

If there are 0.75 mole of CO2, how many molecules are there?

       0.75 moles CO2 x    6.022 x 10^23 particles  = 4.5 x 10^23 molecules of CO2

                                                          1 mole

Now that you know how many molecules are in CO2, how many atoms of Oxygen are there?

4.5 x 10^23 molecules CO2 x   2 atoms of Oxygen     = 9.0 x 10^23 atoms of O

                                                        1 molecule of CO2

2) Converting between moles <--> grams. Remember in this type of conversion we use the molar mass.

    a) Moles--> grams
     # of moles x molar mass = # of grams
                                1 mole

Note: To find the molar mass, look at the periodic table for the atomic mass.


Ex. If there are 2.04 moles of Carbon, what is the mass?
             2.04 moles x   12.0 g   = 24.5 g of Carbon
                                      1 mole

    b) Grams --> moles

      # of grams x      1 mole      = # of moles

                                molar mass        

Ex. If there is 3.45 g of Carbon, how man moles are present?

                 3.45 g x     1 mole      = 0.288 mole of Carbon

                                     12.0 g

Another example: If there are 6.2 g of MgCl2, how many moles are present?

6.2 g x     1 mole      = 0.065 mole of Mg Cl2

                  95.3 g

Whewww, that's a lot of info..time for a chem joke!

What does Avogrado put in his hot chocolate?

Marsh-mole-ows!

KEKEKE. ;P

It's time for the MOLE :D

What you need to know is...
- equal volumes of different gases has a constant ratio.

Do you know who Amedeo Avogadro is?

It's this guy right here!

His hypothesis is that equal volume of different gases at the same temperature and pressure have the same number of particles! 

Like this! 

So if the particles are the same then the mass ratio is the mass of the particles.

ATOMIC MASS:

- The units for atomic mass are amu , u or daltons.

FORMULA MASS:

- All the units of all atoms in ionic compound are in amu.

MOLECULAR MASS:

- All the units of all atoms in covalent compounds are in amu.

MOLAR MASS:

- molar mass contains atomic/molecular/formula mass and are in grams per mole (g/mol)

       ex. 1 mol of potassium = 39.1

Any pure substances have the same numbers of particles.

This is Avogadro's number: 6.022× 10^{23  PARTICLES} 

                                                                     ^MOLE

FUN FACTS:

Speaking of MOLES... did you know that there's something called a MOLE DAY! 

There's also a "anthem" for that day too! 

Check it out!!!

OHHHH NOOOOOO.. test next class D;

Today in class, we received a review sheet to review for our test next Monday. The material in the test includes: sig figs, uncertainty, measurement, graphing, density, scientific notation and unit conversions.

We worked on the review sheet for a while and spent the last half hour in the computer lab making three graphs on excel and completing a worksheet about the graphs.

Chem Joke of the day!

Teacher: What is the formula for water?

Student: H, I, J, K, L, M, N, O.

Teacher: Thats not what I taught you..
Student: But you said the formula for water was H to O...

LAB 2E QUIZ and GRAPHING FUN!

Today there was a Lab 2E Quiz. It covered the experiment we finished the previous day, in which we determined the thickness of aluminum foil.

Some important formulas to remember:

Density = mass/volume

Volume = length x width x height (which also happens to be thickness)


Don't forget that 1cm^3 = 1mL

You can also refer to the previous post for the Percent Experiment Error formula.

NOW ON TO GRAPHING!!!

One of the fundamentals in sciences and physics is learning how to express your data. Today, we were able to create graphs using Microsoft Excel.

Here are some instructions accompanied by screen shots that I took:

1) Enter your x values.
2) Under the next column, start by entering an equation that relates x and y. In my case I stated that y=A3(representing the x values) + 2.

 
3) Enter. The y value in accordance to the formula should appear.

4) Next, click on the first y value box. Hover your cursor over the bottom right hand corner. A small plus sign should appear.


5) Drag the plus sign down so that the rest of the y value column is covered.

 6) Enter again. All the y values should appear.

7) Now, highlight all the y values and the x values and click on the graphing icon outlined in green.

8) Customize the graph as you would like it. Keep clicking next, fill in the title, and click finish.

 

9) To add a linear trendline, right click on one of the points and click "Add Trendline." Go to options and click on the box that says "Display equation on chart" if you wish to display the equation.

10) To customize the chart, you can right click anywhere and choose "Format Chart Area."

11) Do a little editing and TADA! You can make your graph beautiful :)

Another great tool that can be used to create graphs or do another neat things is GEOMETER'S SKETCHPAD.

Watch to learn how to use it!

It's...LAB TIME...again..

For some reason, I end up always doing the blog on the day we do a lab...
Anyways, the lab was determining aluminum foil thickness. For this lab, the thickness will be an indirect measurement because we can't directly measure the thickness since it's so thin. So to determine the thickness, we used 2 formulas.

Volume: V=LWH (Length x Width x Height)
Density: D=m/V (mass/volume)

The density formula is first used because we know the density of aluminum and mass. This gives us the volume. Next, is to figure out the height (thickness). We can do that by using the volume formula since we know the volume and length and width. An example would be:
If you're given this information...density of the aluminum foil is 2.70 g/cm^3, length= 15.57 cm, width= 13.56 cm, and mass is 0.85g, what is the thickness?

If D=M/V then it would be... 2.70g/cm^3= 0.85/15.57 x 13.56 x H

570.04884H=0.85

H= 0.0014911

= 1.49 x 10^-3 cm

Once, the thickness was determined for all 3 sheets of aluminum foil, we found the average. We gave it in proper scientific notation and with the right amount of sigfigs. Then we compared it to the accepted value by comparing how accurate we were and how precise. To find the percent experimental error...

 

On the other hand, here's a little cartoon to lighten the mood? =P

Guess What?? IT'S DENSITY TIMEE!!!!

Ready for some Density? OKay! 

First of all, the formula for density is.. Density =Mass

                                                                  volume

Other ways to write the formula are...

V = m       or       m = DV

       D

REMEMBER:
solid is g/cm3
liquid is g/mL
1 cm3 of water = 1mL

Density of water is 1000 g/L or 1.0 g/mL

If the d objeect < dliquid then it's floating

If the dobject is >dliquid then it's sinking

Here's an example question! 

In a balloon, helium occupies 3.5 L with a mass of 4.0 g. What is the density?

Ans: D = m/v = 4.0/3.5 = 1.1g/L

Now that you've done all these density things, it's time for something fun! Try this if you want!