Percent Composition

The percent composition of a compound is a relative measure of the mass of each different element present in the compound.

These are the rules on how to calculate the percent composition;

Calculate the molecular mass of the compound

Calculate the total mass of each element present in the formula of the compound

Calculate the percent compositon (percentage composition): % by weight (mass) of element
= (total mass of element present ÷ molecular mass) x 100

Examples.
1.Calculate the percent by weight of sodium (Na) and chlorine (Cl) in sodium chloride (NaCl)
Calculate the molecular mass (MM):
MM = 22.99 + 35.45 = 58.44


Calculate the total mass of Na present:
1 Na is present in the formula, mass = 22.99


Calculate the percent by weight of Na in NaCl:
%Na = (mass Na ÷ MM) x 100 = (22.99 ÷ 58.44) x 100 = 39.34%


Calculate the total mass of Cl present:
1 Cl is present in the formula, mass = 35.45


Calculate the percent by weight of Cl in NaCl:
%Cl = (mass Cl ÷ MM) x 100 = (35.45 ÷ 58.44) x 100 = 60.66%


Note: If the answers add up to 100 they are probably correct.

2.A compund has a total molar mass of 18g/mol and a % composition of oxygen and 11.1% hydrogen. How many oxygen atoms are there in the compound?
11.1/100 x 18g/mol = 2.0g/mol = 2 hydrogen

100-11.1=88.9/100 x 18g/mol = 16 = 1 oxygen

There is one oxygen atom in the compound

3.A school boy buys a bag of candy. Each piece of candy contains 5g of glucose (C6 H12 O6). A) find the % composition of glucose B) if the bag contains 150g of candy, does the percent composition of the glucose change? Explain.

a)MMg=180g/mol

C6 = 72/180 x 100 =40%

H12 = 12/180 x 100 = 7%

O6 =96/180 x 100 = 53%

b)No, because the % composition is based on each individual compound and will not affect the candy as a whole. The % composition will not change because if each piece of candy is the same than the composition will stay the same because the numbers will be larger but will have the same ratio.

4.A molecule has a mass of 142g. It contains 5 atoms of one element and 2 atoms of another. What is the other element if one of them is oxygen and oxgyen has five atoms? What is the percentage composition of both elements?

Oxygen: 16 X 5 = 80g

142g-80g=62g

62g/2=31g

**Check for a component with the atomic mass of 31g. 

Phosphorus=31g. 

Check by firguring out the percent composition. 

62/142=43.7%            43.7+56.3=100g.

80/142=56.3%

Answer= P2O5

5.Calculate the molecular mass (MM) of (NH4)3PO4:


MM = 3x[14.01 + (4 x 1.008)] + 30.97 + (4 x 16.00) = 3 x [14.01 + 4.032] + 30.97 + 64.00 = (3 x 18.042) + 30.97 + 64.00 = 54.126 + 30.97 + 64.00 = 149.096


Calculate total mass of N and then the percent:
3 N are present, mass = 3 x 14.01 = 42.03
%N = (mass N ÷ MM) x 100 = (42.03 ÷ 149.096) x 100 = 28.19%


Calculate total mass of H, and then the percent:
12 H are present in the formula, mass = 12 x 1.008 = 12.096
%H = (mass H ÷ MM) x 100 = (12.096 ÷ 149.096) x 100 = 8.11%


Calculate the total mass of P and the percent:
1 P is present in the formula, mass = 30.97
%P = (mass P ÷ MM) x 100 = (30.97 ÷ 149.096) x 100 = 20.77%


Calculate the total mass of O and the percent:
4 O are present in the formula, mass = 4 x 16.00 = 64.00
%O = (mass O ÷ MM) x 100 = (64.00 ÷ 149.096) x 100 = 42.93%


The answers above are probably correct if %N + %H + %P + %O =100, that is,
28.19 + 8.11 + 20.77 + 42.93 = 100

Check out this video!
http://www.youtube.com/watch?v=xbEeyT8nK84
Search up some problems to help you through this!

Quiz Day

WE HAD A QUIZ TODAY.

IT ALSO SNOWED

AT LEAST 5CM!

WE'RE DROWNING

-gargle gargle-

the quiz was on mole conversions, just in case you forgot/ missed it

i have no cookies for you

....

i have a mole game?
while i'm at it, this blog has been lacking puns..

-JY

Harder Mole Conversions

Begin with a mole map:

Conversion from particles to mass (g)
Ex. What is the mass of 1.27x10^22 Co atoms?
1.27x10^22 atoms x (1mol/ 6.022x10^23atoms) x (58.9g / 1 mol) = 1.24g of Co

Conversion from grams to particles

If you have 10.0g of Iron how many atoms do you have?

10.0g x (1mol/55.8g) x (6.022 x 10^23/ 1 mol) = 1.08 x 10^23

Basically just follow the steps on the mole map and make sure you cancel out the units using the fractions method depicted above.

If your doing some work at home you can use this website to check some of you answers:
http://www.convertunits.com/from/grams/to/moles

Video of grams to mole conversion:
http://www.youtube.com/watch?v=ehepBBtSbDc

Video of mole to grams conversion:
http://www.youtube.com/watch?v=NMdN1LtHuDA&feature=related

Thank you!
KP

Mole Conversions: Part I

Good Evening my vaguely hostile readers!

today we will be learning how to convert

 into  .

"is this a joke?" asked the skeptical reader.

Well my dear reader, of course it is! We all know that moles don't like lotus roots!

(if anyone gets that reference, you will be forever endowed with cookies, love and my respect)

And before I am burned at the stake for creating such an obscure joke, we will introduce conversions from particles and grams to moles and vice versa. (IS IT GETTING HOT IN HERE OR IS IT JUST ME?)

Before we begin, there are a few ideas/definitions that need to be known:

Atomic Mass

• in ATOMIC MASS UNITS (u)
• the relative mass of atoms compared to the Carbon-12 atom

Formula Mass

• in (u)
• total mass of all atoms in an ionic compound
• to find formula mass
1. count the number of atoms of a single element
• keep the elements separate, if that wasn't obvious enough while counting (DON'T START BURNING MY HAIR, I'M NOT DONE TEACHING. THANK YOU)
2. multiply the by the atomic mass of that element
3. add the masses of all elements with significant figures

Molecular Mass

• in (u)
• total mass of all atoms in a covalent compound, organic, or polyatomic element
• to find molecular mass
• follow steps displayed above

Molar Mass

• mass of one mole of a substance
• the same numerical value as atomic, formula, or molecular mass...
• ...but is expressed in grams/mole (g/mol)

Now that we have laid out some key ideas/definitions, we can now begin conversions!

(and if i stall long enough, maybe your fires will go out. ARGGH I KID I KID)

Conversions Between Particles and Moles

• remember the formula 6.022 x 10^23 particles/ 1 mole
• To convert from particles to moles
• we'll use 3.01 x 10^24 particles of carbon as our example
• we want to get rid of the particles in the formula stated above
• 3.01 x 10^24 particles (1 mole/ 6.022 x 10^23 particles)
• so we divide!
• to get our answer: 5.00 moles
• To convert from moles to particles/molecules/formula units/atoms
• we'll use 0.75 moles of Carbon Dioxide into molecules
• 0.75 moles x (6.022 x 10^23 molecules/ 1 mole)
• so we multiply!
• to get our answer: 4.5 x 10^23 molecules of Carbon Dioxide
• when asked to find more than one type of atom
• count the amount of atoms wanted to be found 
• multiply it by the answer found above
• (2 atoms of Oxygen/1 molecule of Carbon Dioxide) x (4.5 x 10^23 molecules of Carbon Dioxide)
• to get our answer: 9.00 x 10^23 atoms of oxygen

Conversions Between Grams and Moles

• you will need your trusty periodic table for these conversions
• Is similar to unit conversions
• To convert from gram to moles
• we'll use 3.45g of C as our example
• 3.45g x 1 mole/ 12.0g (molar mass)
• so we divide!
• to get our answer: 0.288 moles of Carbon
• To convert from moles to grams
• we'll use 2.04 moles of Carbon as our example
• 2.04 moles x (12.0g/mol / 1 mole)
• so we multiply!
• to get our answer: 24.5 g of C

So as I continue to burn from the fury of my readers, I leave you a link to a mole to molecule calculator, a link to a grams to moles calculator, and 

(and as the wise mole cricket once said “Take a turn at every turn you encounter on your way.")

-JY

The Mole

What is a Mole?
A mole is simply a unit of measurement. Units are invented when existing units are inadequate. A pure substance that containg the same number of chemical usints as there are in atoms. (i.e., 6.022 X 10^23)


Different gases have a constant ratio
-oxygen : hydrogen      16:1     <---these numbers are the atomic weight

Avogadro's Number!

 Avogadro's number, also known as Avogadro's constant, is defined as the quantity of atoms in precisely 12 grams of 12C. The designation is a recognition of Amedeo Avogadro, who was the first to state that a gas' volume is proportional to how many atoms it has. Avogadro's number is given as 6.02214179 x 10^23. Equal volumes of differest gases at the same temperature and pressure have the same number of particle. 

Relative masses are measured in Atomic Mass Unit, also written like 'amu.'

Formula Mass

Ionic- Add amu's

All atoms of a formula of an ionic comound (amu). When figuring out the atomic mass units, be sure to add the mass of each atom.

Ex.,  Potassium Fluoride
             K           F
           39.1       19
     39.1+19= 58.1amu

Molecular Mass
Atoms of a formula in covalent compound (amu)
Ex. Carbon Dioxide
         C         O2
      12.0   +    (16.2 X 2)
           =44amu

Molar Mass
Atomic/molecular/formula mass of any pure substanse (g/mol)

Ex. What is 1 mole of oxygen?
       Answer: 16g/mol


Check out this video guyss ! Thanksss!
http://www.youtube.com/watch?v=zWmyLsGBEDE&feature=related

Graphing the Density of Water

Today we had a short at the beginning of class on the lab that we preformed last day.
Then we went into the computer room and started graphing data that ms. Chen collected during our quiz.

How to Graph Data
Open excel and create a two columns, one for mass and the other for volume.
Then adjust the values so they are correct.
Then highlight the values for your graph and click create graph.
Select scatter (x,y) graph
Edit the special options such as the title, axis and legend (you can also change the colours!)
Right-click one of the data points and select create trend line. A line of best fit will appear
Now highlight the trend line and select show formula. The formula for the trend line will appear.

Our Results:
Using this method we compared the density of cold water to the density of hot water. We found that cold water had a density of 1.34g/cm3 and that hot water had a density of 1.04g/cm3.
Hot water has a lesser density than cold water because the particles are more spread out due to more energy in the substance.


The blue is cold water which is more dense so it stays at the bottom. The red is hot water which is less dense so it floats near the top


Here is a really good video explaining water density
http://www.youtube.com/watch?v=Ak9CBB1bTcc


KP

Lab: Determining Aluminum Foil Thickness

Worry not friends! The aluminum foil will always protect us from aliens, no matter the thickness!

In this lab we apply the formulas learned last post into 'real life situations.' I mean, who doesn't worry about the possible threat of mind control and mind-reading when the thickness of their aluminum foil is --?

For this lab let's say that we do not have a micrometer available, and only a centigram balance, a ruler and 3 pieces of aluminum foil (of relatively the same size) at our disposal. 

So skeptical tin -foil hat wearing reader? How DO we find the protection level of your hat?

Let's start off with information that can possibly given to you:

• the density of aluminum foil is 2.70g/cm^3
• you have a ruler and 3 pieces of aluminum foil

Do not be so pensive, readers! 

Measuring the length and width of your aluminum foil, you can now start to feel much safer!

Remember volume can be found by:

• length x width x height (but in this situation, it is thickness)

OR 

• by mass/density ( which is given to you 2.70 g/cm^3)

And as a concerned citizen of mankind, I feel it is my duty to guide you to a feeling of safety and assurance with your tin foil hats.

You can now find the thickness of your protective headgear with simple math! As you now have:

• mass
• density
• volume
• width and length

Remember, as a proper citizen of mankind, we must always use the proper amount of significant figures when speaking about our tin foil hat thickness.

Also as a hint to my brothers, the accepted value of aluminum foil thickness is 1.55 cm.

Ah! But wait, you ask about errors within your experiment?

Well my troubled reader, worry not! You can find your experimental error with this simple formula:

experimental error = average measurement - accepted value x 100

                       accepted value

With all this information, I believe that I can safely assume my tin foil wearing, fellow humans will live on and prosper!

and for those who lack proper protection from the supernatural, i give you this! a magical link that will not allow me to read your mind!


-JY (I am sad to say, I can no longer read the minds of my readers)

Density

What is density? Well density is the amount per unit size. Density is a physical property of matter
You can use density in everyday life, like swimming for example.

Density= Mass/Volume <-- This formula is interchangeable, we can also use this formula to find the mass and or volume.
For a solid the units for density would be g/cm3.
For a liquid the units for density would be g/mL.
Example.
Volumer=Mass/Density and Mass=(Density)(Volume)
**Remember, if the density of an object is greater than the density of the liquid, it would sink. If the density of an object is lesser than the density of the liquid, it would float.

Watch this! Good song on how to remember the density formula!
http://www.youtube.com/watch?v=TRkCz3zG7w0&feature=related