Percent Composition %

WELL! Today we learned something new. Something Fresh. Something that sounds harder than it really is!
Percent Composition is a relative measure of the mass of each different element present in the compound.

A formula that may help is : % Composition = Mass of element / mass of compound x 100

Here is an example:
1) Calculate the % composition of NaCl
    1. Find its molar mass: 22.99 + 35.45 = 58.44
    2. Calculate the amount of Na: 1 Na = 22.99
    3. Calculate the weight compared to NaCl: 22.99/58.44 = 39.34%
    4.  Calculate the total Cl present : 1 Cl = 35.45%
    5. Fine the weight compared to NaCl: 35.45/58.44 = 60.66%
* Note: Weight MUST add up to 100%, if not then there is an error in the calculations

Practice Questions:

1.Calculate the percent by weight of each element present in ammonium phosphate [(NH₄)₃PO₄]

2. Bicarbonate of soda (sodium hydrogen carbonate) is used in many commercial preparations. Its formula is NaHCO₃. Find the mass percentages (mass %) of Na, H, C, and O in sodium hydrogen carbonate. 

Well! It is pretty straight forward. This is pretty much what we learned all class!

Here is a very instructive video on how to calculate percent composition if it still confuses you!

http://www.youtube.com/watch?v=xbEeyT8nK84

Mole Conversions

Today we practiced our mole conversions. The first step to this is calculating molar mass.
Add up all the molecular masses of the compound:
Ex. H2O ---->
mass of 1 oxygen atom = 16.0g

mass of 2 hydrogen atoms = 2.0g

16.0+2.0 = 18.0 therefore the molar mass for H2O is 18g/mol

Remember to use Avogadro's number when converting Particles/atoms/molecules

We also did some examples in class from our Mole Conversions Exercise A-C, this involved converting:
Moles to particles/atoms/molecules
Particles/atoms/molecules to moles
Moles to grams

Ex.. Moles to atoms

How many atoms are present in 3 moles of sulphur

3 moles S x 6.022x1023/1 mole = 1.81 x 1025 Atoms


Ex. Atoms to moles

How many moles of Al are present in 2.6 x 1012 atoms of Aluminum

2.6 x 1012 atoms Al x 1 mole/6.022 x 1023 atoms = 4.32 x 10-12 Moles


Ex. Moles to grams

What is the mass in grams of 12 moles of Fluorine gas

12 moles Fl  x 19g/1mole = 228g of Fluorine

Harder Mole Conversions

We learned how to do harder mole conversions.

This means converting from moles to number of atoms for example, where there are multiple steps involved.
One helpful way to do this is to use a mole map.

Here is an example:

Grams----------> Moles----------------> Number of Particles------> #  of Atoms in a Particle



To do this you need to know the operations involved in conversion.

Grams to moles = 1mole/ MMG
Moles to Number of Particles= 1 mole/ 6.022 x 10^23 particles
Number of Particles to Number of atoms = Number of atoms in a particle / 1 molecule of that substance

Going the other way, everything is flipped.

Number of atoms to number of particles= 1 molecule of that substance/ number of atoms in one particle
Number of particles to moles= 1 mole/6.022 x 10^23 particles
Moles to grams = MMG/ 1 mole


Here are 2 examples

Convert 20 g of CO2 into number of atoms of O

First find the molar mass which equals

1 C = 12.0 g/mol
2 O = 32.0 g/mol

so...

20g CO2 x 1 mole/ 44.0g x 6.022 x 10^23/ 1 mole x 2 atoms O/1 molecule CO2=

= 5.47 x 10^ 23 atoms of O



2) Convert 2.34 x 10^ 23 molecules of CaCO3 into grams

= figure out Molar mass of  CaCO3
= 1 Ca = 40.1 g/mol
=1 C =12.0g/mol
=3 O = 16.0 g/mol

= 100.1 g/mol

so ..

2.34 x 10^23 molecules of CaCO3 x 1 mole/6.022 x 10^23 particles x 100.1 g/ 1 mole =

= 38.9 g CaCO3

Thursday was rough.

There were numerous reasons why Thursday was a rough day for students. Especially for those in grade 11 Chemistry. First of all, we had school. There was a mighty blizzard outside that was life-threatening to many, yet we still had to bust our behinds to school. Not only that, we had a Moles quiz. If you think that is bad, which I know it is bad, without even thinking, we also had a sub. I mean, what is Chemistry 11 without Ms. Chen? Don't even answer. To top it all off, we got 2 worksheets. And that was why Thursday was rough.

Moley Mole

This previous Wednesday's class was a great class. It was such a good class because we saw a video with a great theme song. The song was "Happy Mole Day To You". That was all I learned. Just kidding.
On Wednesday our class was introduced to Amadeo Avogadro's Theory/Hypothesis. Avogadro's theory was that the same amount of different gases at the same pressure and temperature, should contain the same number of particles.
A few examples 2 particles to look at are:
Oxygen : Hydrogen = 16:1
Carbon Dioxide : Hydrogen =  22:1
Carbon Dioxide : Oxygen = 18:1
^^ If the number of particles is the same, the mass ratio equals the mass of the particles. This principal is used for relative masses of all atoms on the periodic table of elements.

There are a few ways to express the measurements of atomic mass. The units possible include amu, u, and daltons.

Molar Mass is the mass of 1 mole; in particles of course. The Molar Mass of an element is the mass labelled on the periodic table shown in grams. Some examples include: **abbreviation for mole = mol!
1 mole of Oxygen is 16.0 g/mol
1 mole of Potassium is 39.1 g/mol
1 mole of Carbon is 12.0 g/mol
^^ all listed above have the same amount of particles!

Lastly, the formula of molar mass is 6.022 X 10 to the power of 23 in grams per mole. {g/mol}

http://www.youtube.com/watch?v=ReMe348Im2w that is the beautiful video we watched.
http://www.animalpictures1.com/r-mole-84-mole-1434.htm and that is a picture of a mole, the animal.

Drawing and Interpreting Graphs Using Open Office

On November 9, 2010 we started reviewing for the big chapter test coming up on Monday November 15.
We were given a review sheet by  Mrs. Chen which covered accuracy and precision, absolute and relative uncertainty, adding, subtracting, multiplying and dividing using significant figures, rounding, scientific notation and unit conversions.

Later we headed down to the computer lab to do some more graph work using Open Office.


First we graphed the volume( mL) of a sample of gas under increasing temperature(K)

We were asked to use a trend line for our scatter plot

We discovered that the slope of our graph was f(x) =0.55x -0.31.

The point (521, 273) was uncertain on this graph, meaning that when temperature was 521 K, and the volume 273 mL, the point was not directly on the trend line like the other points.

In number 2, we graphed the density(g/mL)  of a water sample under increasing temperature(degrees Celsius)

We determined that the density of water increased from 0.99987 g/mL to 1.00000 g/mL when heated from 1 degree to 4 degrees Celsius.
After that though, the temperature continued to increase but the density decreased.

The graph did not illustrate a consistent unitary rate because it was a parabola and was not constant. Density increases then decreases while the temperature consistently rises.

We then graphed the relationship between volume and the mass of several pieces of glass.

We graphed it, and used a trend line. By determining its slope, we determined the density of the glass.

Density of hot and cold water

Hm... what i remember about last class was that we had a spectacular mini quiz on the lab report!!! Oh goodie... more quizzes to bring down my mark! The lab was about Determining Aluminum Foil Thickness. I will not get into any details because the process was thoroughly described in the previous blog.

*PS, I only wrote that it would bring down my mark because i didnt study for the quiz! See!! I'm a very honest person!

The more interesting work that we did was the graphing of the Density of Water! We graphed 2 charts: One for Cold Water and One for Hot Water.

What we did was on Microsoft Excel and we had to make a graph using the calculations given. With hard work and determination, and imagination like a 6 year old, we had to make it as pretty and colorful as possible, pretty much changing everything.

After all the fun stuff, we had to explain what is different between the 2 graphs. After graphing it, we compared the density of cold water to the density of hot water. Cold water had a density of 1.34g/cm3, and hot water had a density of 1.04g/cm3. During class, we discussed why hot water is less dense than cold water, this is because the particles are more spread out. The hot water has more energy,bouncing off each other, therefore being more spread apart, and causes them to be less dense.

We didn't cover a whole lot this class, but this video should help your understanding of the density of water, and the difference it'll make if the density is different.

Lab 2E: Determining Aluminum Foil Thickness

Lab 2E was done in class on November the second. It involved find the thickness of aluminum foil by ways of mathematical formulas.


Equipment:

3 Rectangular pieces of aluminum foil
Centigram balance
Ruler


Procedure:

Obtain 3 pieces of aluminum foil. The foil was then measured twice for both width and length on each end to determine to average length of the side. This was done to minimize experimental error.A centigram balance was then used to find the mass of each piece of aluminum foil.


Results:

The thickness of the aluminum foil was determined by two algebraic equations.
D (density) = m/V (mass/volume)
V = LWH ( length x Width x Height)

The mass, length and width were all known from previous measurements taken in the lab. The mathematical procedure was as follows:


D = m/V

2.7 = 1.04/(16.8)(14.55)(h)
2.7 = 1.04/244.44(h)
(244.44h)(2.7)= 244.44h(1.04/244.44h)

The 244.44h's then cancel on the right side.

687.204h/687.204= 1.04/687.204
h = .001513378
h = 1.51 x 10^-3cm

This same operation was performed for all three pieces of aluminum foil because each had a different length and width then the other two.

New Month, New Mentality.

What? MCJC writing their blog the night of Chemistry Class?! No Late Cramming?! I'm not going to lie, I think I have a fever this is so weird. Anyway, today was the first day of November, and we were brutally welcomed to the 11th month of the year to a thrilling quiz that was so much fun I almost felt like writing it again! Okay, it is 6 months until April fools, why not throw in a joke? Moving on, after our spantastic quiz on Significant Figures, we took some beautiful written notes on Density. Now even though I am one of the brightest scientists you will ever meet, I will tell you about these notes we were given.

The Density of a substance is also know as its mass over volume. To calculate an object's density, you quite simply divide mass over volume. D = m/v

Now for most non-scientists, this is where it gets tricky. Well, not really. It just sounds cooler when I say that and when I hear/read that, more often then not I actually decide to listen rather than just pretend to.

For a solid substance, the most commonly used measurement is g/cm3.
For a liquid substance, it is usually g//mL. *** 1 cm cubed of Water = 1 mL

So we know how to calculate the Density, and the units, but what next?

Well, if the density is greater than the liquid's, than the object will sink.
If the density is less than the liquid's, the object will float.

Object > Liquid = Sink
Object < Liquid = Float.

You want an example? I don't. But here is one.
Eg. Calculate the density of an Iron Bar if the bar weighs 1200 grams, with a volume of 1.25L.

D= m/v D = 1200g/1.25L
D = 960 g.
** REMEMBER the units, grams and Litres.

That is all!!! YAY!!!


Here are a couple of videos that we found helpful....

http://www.youtube.com/watch?v=rxb_6UANXqU

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



ENJOY!