Density conversion:

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

1. question: Water has a density of 1.0g/ml. Determine the mass of 11.5ml of water

                     How many moles are in 11.5 ml of water?

    answer: 10g/ml x 11.5ml=11.5g=12g

                  11.5g x 1mol/ 18.0g=0.64 mol

2. question: An unknown compound has a molar mass of 65.0g/ mol. If 0.25mol occupies 

                    a volume of 50ml determine the compound's density

    answer: 0.25mol x 65.0g/ mol= 16.25g 

                  16.25/50ml= 0.325g/ml= 0.33g/ml

3. question: The density of aluminum is 2.70g/ml. A solid piece of aluminum has a volume

                     of 45.0ml. Determine the number of aluminum atoms present

    answer: 2.70g/ml x 45.0ml x 1mol/27.0g x 6.02 x 10^23 atoms/ 1 mol

                  = 2.71 x 10^24 atoms

4 question: Copper has a density of 8.96g/ ml. Determine the numbers of atoms in a copper

                   key that has a volume of 20ml TRY THIS YOURSELF!! :D

Density of gases:

1. The density of gases varies with temperature 

2. An STP we can find density by: 

    MM [molar mass]/ 22.4 l/mol [molar volume]

1. question: Calculate the density of 0,2 at STP

     

    answer: 32.0g/mol / 22.4l/mol=1.43g/L 

2. question: Determine the density of methane[ CH,4] at STP

    answer: 16.0g/mol / 22.4L/mol=0.714g/L

Stoichiometry

Hello fellow subscriber... and viewers! Today we learned about the Quantitative Chemistry - Stoichiometry.

....What? What is Stoichiometry? WELL it is a branch of chemistry that deals with the qualitative analysis of chemical reactions.

To understand Stoichiometry, our teacher reviewed us on the 6 types of reactions (not including complex reactions that doesn't go under the 6 common reactions). This is what we learned in grade 10; last year.

Ok, so there are 6 common types of reactions
1) Synthesis (Formation)
2) Decomposition
3) Single Replacement (SR)
4) Double Replacement (DR)
5) Neutralization
6) Combustion

Here is a breakdown of each reaction:
1)Synthesis : Basically a reaction to make compunds; so the equation would be-
A+B=AB

2)Decomposition : The opposite of Sythesis, which breaks down compounds.
AB= A+B

3)Single Replacement: When an element switches with another element in the equation, similar to this:
A+ BC=B+AC

4)Double Replacement: When both elements switch... like this
AB+CD=AD+BC

5) Neutralization : A reaction between an acid and a base, to form a compound and HOH
ACID+BASE= COMPOUND + HOH

6)Combustion: A reaction usually dealing with a hydrocarbon, that ALWAYS produces CO2 and HOH
Hydrocarbon + Oxygen = CO2 + HOH

There we have it, introduction to the world of Stoichiometry! Tune in next time for more!

PERCENT COMPOSITION

-the percentage by mas of an elemet in a compund is always the same
-to find the percent by mass determine the mass of each element present in one mole

http://www.youtube.com/watch?v=CGQoQk-xZ68

Empirical & Molecular Formulas

EMPIRICAL FORMULAS: 

  The simplest formulas of compounds are called Empirical Formulas. They do not show the actual number of atoms but rather the simplest ratios the compound has.

EXAMPLE:

Where Nitrogen can be written as N2 when alone, it's empirical formula would just be N.

Similarly, where Dinitrogen Tetraoxide is written as N2O4, it's empirical formula would just be NO2.

  To determine the empirical formula, we need to know the ratio of each element. For that we will need to prepare a table to help us:

Atom | Mass | Molar Mass | Moles | Smallest Mole | Ratio 

EXAMPLE:

Let's start with 4.58 g of Silicon and 5.21 g of Oxygen.*

*You can find this example and others on: http://homepage.mac.com/sklemmer/Honors/empformulawkst.htm 

1. Create a table.

 Atom | Mass | Molar Mass | Moles | Smallest Mole | Ratio 

2. Fill in the table with what you know. To figure out the number of moles, find the molar mass of each element.

Atom | Mass | Molar Mass |   Moles   | Smallest Mole | Ratio 

Si       4.58 g   28.1 g/mol    0.163 mol

O        5.21 g   16.0 g/mol    0.326 mol

3. To fill in the column for the ratios, you will need to use your smallest mole. What this means is that you take your smallest value of moles which would be 0.163 mol in this case, and divide it from the number of moles of each atom.

Atom | Mass | Molar Mass |   Moles   | Smallest Mole | Ratio

Si       4.58 g   28.1 g/mol    0.163 mol÷0.163= 1          -> 1

O        5.21 g   16.0 g/mol    0.326 mol÷0.163= 2          -> 2

4. Write out the final formula with the ratios in the place of the subscripts. This will be the empirical formula.

SiO2

MOLECULAR FORMULAS:

  While empirical formulas give the simplest ratios, Molecular Formulas give the actual number of atoms. To know the molecular formula, you would need to know the empirical and molar mass.

EXAMPLE:

Empirical   |   Molecular 

C2H6O                ?

     ?              138 g/mol

1. Calculate the molar mass of the Empirical Formula and place it in the table.

Empirical   |   Molecular 

C2H6O                ?

46 g/mol         138 g/mol

2. Figure out the number of times 46 goes into 138 to find out the multiplier.

138÷46= 3

3. Use the multiplier as a co-efficient for the empirical formula and expand. This will give you the molecular formula.

Empirical        |       Molecular 

C2H6O-> 3(C2H6O) -> C6H18O3

46 g/mol               138 g/mol

*For more information on Empirical and Molecular Formulas check out this link:

http://www.youtube.com/watch?v=gfBcM3uvWfs

MOLAR VOLUME LAB: [ russel m., aaron l., and trevor n.]


The task in this lab was to experimentally determine the molar volume of a gas


Materials: Butane, Sink, Water , 100mL Graduated cylinder, Weigh scale


Prelab:
The chemical formula for butane is C4H10
The molar mass for butane is 74g


Analysis: The mass of butane lighter before the experiment was 21.65g
                The mass of the butane lighter after the experiment was 21.40g
                The mass of butane used in the experiment was 0.25g
                There were 0.004 moles of the mass of butane 
                The molar volume of butane is 12.5L/mol

Molar Volume Lab

Hello again!
We did a Molar Volume Lab before the Winter Break and it contained a sink full of water, a graduated cyliner, and a lighter with a substance called Butane which is known for its combustive traits. But in this lab we measured how much Butane is consumed  underwater on top of a graduated cylinder. This sets us up with our estimated "STP" or Standard Temperature and Pressure, which is 22.4. None of our classmates were near to the number but one of the groups recorded a 24.2, which was SATP.

Multi-Step Conversions

  Sometimes, there will be cases where you will be given information that you would have to use in order to make numerous conversions. Here are some examples:

EXAMPLE:

12.5 grams of Hydrogen (H2) are placed in a balloon at STP (Standard Temperature and Pressure = 0º C & 101.3 kPa). Determine it's volume.

1. First, use molar mass as your conversion factor and cancel accordingly.

-> 12.5 g of H2    x    1 mol     
                               2.0 g*


*The mass in grams is 2.0 because there are hydrogen is diatomic.

2. Next, use molar volume as your conversion factor and cancel accordingly.

-> 12.5 g of H2    x    1 mol    x    22.4 L
                               2.0 g           1 mol

3. Alter your answer to have the appropriate number of significant digits.

-> There are 1.4 x 10² Liters in 12.5 grams of Hydrogen.


   There will be other instances where they ask you for more conversions such as grams to atoms or liters to molecules. The most important thing to do is to first recognize what you have and what your answer's units should be. From there, you can decide on you conversion factors. Here are some of them:

Molar Volume (of all gases @ STP):
22.4 L / 1 mol

Molar Volume (of all gases @ SATP-> Standard Ambient Temperature & Pressure):
24.8 L / 1 mol


Molar Mass:
grams (g) / 1 mol


Avogadro's Number:

6.02 x 10²³ molecules or atoms or fundamental units / 1 mol

  Here are some links to help you out as well:
http://www.youtube.com/watch?v=tS9l-OxucQU
http://www.youtube.com/watch?v=AsqEkF7hcII&feature=related
http://www.youtube.com/watch?v=8TkY36qB1f0