Molarity

Molarity is the concentration of an element or compound in water. Molarity is known as M or mol/L.
The higher the molarity the more concentrated an element or compound is.

Molarity is easily calculated by finding how many moles are present and then dividing by the volume ( in litres). Simply if there are 2.5 moles present of a compound and the volume is 10 litres the molarity is 2.5/10 or .25 M.

Empirical & Molecular and Percent Composition

Empirical fomulas are the simplified versions of compounds.
For example C3H9 can be simplified to CH3 and on the otherhand molecular formulas are the unsimplified versions of empirical compounds like C3H9

Empirical and molecular formulas can be expressed as percent compositions.
For exmaple water is 89% oxygen and 11% hydrogen. Though more hydrogen atoms are presesnt in the formula H2O the percent compisition is based on the masses of atoms divided by the total mass of the compound.

For H2O the percent composition is determined by:
Oxygen = 16 g/mol
Hydrogen = 1g/mol
Total mass = 16 + 2 (2 hydrogen atoms are present)

Oxygen % = 16/18 or 89%
Hydrogen %= 2/18 11%

With organic compounds that are burned it is possible to find out how much of each atom was present in the beginning of the reaction and after.

If a 6.5 gram sample of C and H burn to produce 20.5 grams of CO2 and 8.4 grams of H2O
You can figure out the empircal or molecular formula by finding how many moles are present of each compound.

There is .466 mol of CO2 (remember mole conversions)
And .467 mol of H2OIf you divide by the lowest mole amount you can get how many of each compound are present.
.467/4.66 = 1
.466/.466 = 1
So theres about 1 of H2O and CO2
And knowing this simple ratio of xCHy + O2 = xCO2 + (y/2)H2O
In this case it would be 1CH2 + 2O2 = 1CO2 + 1H2O
And to find the oxygen is as simple as adding the oxygens present on the the right side of the formula and dividing by two.

Mole Conversions 2 Steps

Converting can be done from grams to moles to particles and vice versa step by step or in a two step conversion.

It's possible to go from particles to grams and grams to particles using the simple mole conversions
For example:
6.24 grams of NO3  To particles.
First you would need to find the molecular mass by finding the atomic mass of each seperate element and adding them. The molecular mass in this case would be 60u.

Next you would go from grams to moles and then to particles by

6.24 g x 1 mol/60 g x 6.022x10^23/1 mol
=6.3x10^22 particles (don't forget sig figs)

Mole Conversions

Grams => Moles
= *1mol/ (?)g

Moles => Formula unit/ Particle/ Atoms
= *( 6.022*1023)/1mol

Formula unit/Particle/Atoms => Moles

=*1mol/( 6.022*1023)

Moles=> Grams
=* (?)g/ 1mol

1. How many moles of Ag are present in 3.0*1016 atoms of Ag?

3.0*1016  *1mol/( 6.022*1023)
= 5.0*10-8 Ag atoms

2.  How many atoms are present in 2 moles of carbon?

2moles C*( 6.022*1023)/1mol
= 1*1024 atoms C

3. What is mass in grams of 1.41 moles of Iron?
Atomic mass of Fe= 5.845u
Molar mass of Fe= 5.845g/mol
1.41mol Fe * 5.845g Fe/ 1mol Fe = 8.24g Fe

4. How many moles are there in 92.0 grams of lead?
Atomic mass of Pb = 207.2u
Molar mass of Pb = 207.2g/mol

92.0g Pb * 1mol Pb/ 207.2g Pb = 0.444 mol Pb

Lab 2E

Lab 2E: Determining aluminum foil thickness

Objectives:

l   To calculate the thickness of a sheet of aluminum foil and express the answer in terms of proper scientific notation and significant figures

Supplies:

l   3 rectangular pieces of aluminum foil

l   Metric ruler

l   Centigram balance

We measured the length and width of the aluminum foils using metric ruler, and measured the mass of aluminum foil using centigram balance. We can calculate the volume of aluminum foils by using D=m/v. after we find the volume, we can calculate the thickness of aluminum foils by using V=LWH

For example:

        D=2.70 (g/cm3)

        M=0.98±0.01 (g)

        Length=15. 47±0.01 (cm)

        Width=15.14±0.01 (cm)

V=m/D, 0.98g/2.70(g/cm3)= 0.36cm3

H= v/LW, 0.363/(15.47*15.14)cm = 1.55*103cm

%Experimental error:

Accepted value= 1.55*103cm

｜(1.55*103cm)- (1.55*103cm)｜/(1.55*103cm)*100%= 0%

So our measurement is accurate and precise, because it’s 0% off to the accepted value

Graphing Tables

Graphing Tables
Graphing tables can be helpful when finding density or comparing two things. With a line of best fit it becomes easier to identify the relationship between two things.

In the following graph pennies are compared to their mass:

By plotting points on the graph and then making a line of best fit it is easy to find an average slope. The slope in this case refers to density but can be applied to other things aswell.

Being Dense

Density
Density is the mass of an object divided by the volume.

The simple equation is Density= Mass/Volume or D=M/V

How dense an object or substance is can tell you if it will float or sink in a fluid or if it's just heavier than another substance. Density also shows how close a substances particles are together, leading to solids usually being more dense than their fluid states. Density can also help identify pure substances if known accepted values are compared.