Chapter 10: MOLE

Pj Hamill (287-288)
Brandon Boisclair (289-291)
Olivia Richardson (292)
Nate Lynch (293) CO-editor
Alex Nunan (294)
Dakota Pimentel (295-296)

PJ HAMILL (287-288)
Measuring Matter -
Key Vocab -

• Mole
• Avogadro's Number
• Representative Particle
• Molar Mass

People often measure the amount of something by one of three methods-by count, by mass, or by volume.
'
Brandon Boisclair (289-291)

What is a Mole?
A unit of measurement, a mole of a substance is 6.02 x 10^23

This number was developed byy Avogadro and is now known as Avogadro's Number.
- He helped clarify the difference between atoms and molecules.

REPRESENTATIVE PARTICLE - refers to the species present in a substance: usually atoms, molecules, or formula units.

CONVERSION:

moles= representative particles X . 1 mole
6.02 x 10^23 representative particles

Olivia Richardson (292)

Converting Moles to Number of Atoms and Particles
Sample Problem:

• Propane is a gas used for cooking and heating. How many atoms are in 2.12 mol of propane? (C3H8)?
• This problem is a mole conversion problem where we will have to use Avogadro's Number which is 6.02 X 10^23
• There will be two conversion factors in the problem. The first is 6.02 X 10^23 molecules of C3H8 / 1 mol C3H8 The next conversion factor will be 11 atoms / 1 molecule C3H8. The destination of the problem is atoms and the starting point is 2.12 mol C3H8.
• This is what the problem should look like all set up: atoms=2.12 mol C3H8 X 6.02 x 10^23 molecules C3H8 / 1 mol C3H8 X 11 atoms / 1 molecule
• After the process of dimensional analysis and solving the equation the answer will be 1.40 X 10^25 atoms
• Here are some more practice problems: How many atoms are in 1.14 mol SO3? How many moles are in 4.65 X 10^24 molecules of NO2?

Dakota Pimentel (295-296)
Mass of a Mole of a Compound

• To find the mass of a mole, the empirical formula of the compound must first be observed
• You need to count the amount of molecules for each letter.
• You need to find the atomic mass of each element and then multiply that number by however many molecules of that element are present in the compound
  • ex: H2O=
    • H --->2 --> 2*1.003
    • O --->1--> 1*16
• Then add all of the elements in the compound to get the molar mass and add grams
  • 2.006+16=18.006---> [18.006g]
• "to calculate the molar mass of a compound, find the number of grams of each element in one mole of the compound. then add the masses of the elements in the compound"

http://www.wisc-online.com/objects/ViewObject.aspx?ID=GCH4104

moleformula.gif

Elizabeth Howard (297)
The Mole-Mass Relationship-Elizabeth Howard Page 297

• The molar mass of any substance is the mass in grams of one mole of that substance
• Use the molar mass of an element or comp
  
  ound to convert between the mass of a substance and the moles of a substance
• Molar Mass=1 Mole
• Mass (grams) = Number of Moles X Mass (grams) / 1 Mole
• Example: Find the mass of 3.00 mol of NaCl (which has a molar mass of 58.5g/mol
  • Mass of NaCl = 3.00 mol X 58.5 g / 1 mol = 176 g

http://wn.com/chemistNATE - Video explaining the Mole-Mass Relationship




Zoey Killion (298)

Page 298:

Zoey Killion

Converting Moles to Mass

1. Analyze: List the knowns and unknowns.
2. Calculate: Solve for the unknown.
3. Evaluate: Does the result make sense?

Figure 1

Example:
The aluminum satellite dishes in Figure 1 are resistant to corrosion because the aluminum reacts with oxygen in the air to form a coating of aluminum oxide (Al2O3). This tough, resistant coating prevents any further corrosion. What is the mass of 9.45 mol of aluminum oxide?

1. Analyze: List the knowns and unknowns.

Known: number of moles = 9.45 mol Al2O3
Unknown: mass = ? g Al2O3.
The mass of the compound is calculated from the known number of moles of the compound. The desired conversion is moles à mass.
2. Calculate: Solve for the unknown.
Determine the molar mass of Al2O3: 1 mol Al2O3 = 102.0g Al2O3
Multiply the given number of moles by the conversion factor relating moles of Al2O3 to grams of Al2O3.
Mass = 9.45 mol Al2O3 X (102.0 g Al2O3/ 1 mol Al2O3)
= 964g Al2O3
3. Evaluate: Does the result make sense?
The number of moles of Al2O3 is approximately 10, and each has a mass of approximately 100g. The answer should be about 1000g. The answer has been rounded to the correct number of significant figures.
Practice Problems:
Ø Find the mass, in grams of 4.52 X 10-3 mol C20H42.
Ø Calculate the mass, in grams, of 2.50 mol of iron (II) hydroxide.

Caroline Rubino (Co ed

itor) (299)

Page 299: Caroline Rubino

Converting Mass (grams) to Moles

Problem: When iron is exposed to air, it corrodes to form red-brown rust. Rust is iron (III) oxide (Fe2O3). How many moles of iron(III) oxide are contained in 92.2g of pure Fe2O3.

1. 1.) Analyze- list the known and unknown

Known Unknown
-Mass = 92.2g Fe2O3 - number of moles = ? mol Fe2O3
- the unknown number of moles of the compound is caculated from a known mass of a compound. The conversion is mass ---- moles.

2.) Caculate - Solve the Unknown

- Determine the molar mass of Fe2O3 : 1 mol = 159.6G Fe2O3
-Multiply the given mass by the conversion factor relating mass of Fe2O3 to moles of Fe2O3.
Moles = 92.2g Fe2O3 x 1 mol Fe2O3
159.6g Fe2O3
= .0578 mol Fe2O3

3.) Evaluate- Does the result make sense????

- Because the given mass (about 90grams) is slightly larger than the masss of one-half mole of Fe2O3 (about 160g) the answer should be slightly larger than one-half (0.5) mol.

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Mole-Volume Relationship

Shannon Lamy (300)

· The volume of 1 mole of different solids and liquids are different
BUT
o Why? Because gas molecules are free flowing and there is a lot of space, so the actual size of the gas influences the volume of 1 mole far less than for a liquid or solid
Example:

Both are gases with different size molecules, but 1 mole of each has the same volume.


Vs

Both are gases with different size molecules, but 1 mole of each has the same volume

· 1811 – Avagadro Hypothesis – At the same temperature and pressure, equal volume of gases contain equal number of particles, but not necessarily the same size particles

· Volume of gas changes at different temperatures and pressures
Example:

Balloon at room Balloon at cold temperature -volume decreases
temperature
· Because temperature and pressure impact the volume of gas so much, gases are measured at Standard Temperature and Pressure (STP)
· Standard Temperature and Pressure (STP) – temperature of 0 degrees Celsius and pressure of 101.3 kPa
· Key Fact – at STP, 1 mole of any gas has a volume of 22.4
o 22.4 = Molar Volume

Calculating Volume at STP

Evan Sommerich (301)
STP is the relationship that 22.4L = 1 mol.

Volume of gas= Moles pf gas X 22.4 L
1 Mole
A video that explains how to do the conversions
http://www.youtube.com/watch?v=AHqNiEwcXiE
Becky Hyatt (302-303)

Calculating Molar Mass from Density page 302 (Becky Hyatt)
Ÿ a gas-filled balloon will either sink or float depending on whether the density of the balloon’s gas is greater or less than the density of the surrounding air
Ÿ molar mass = density at STP x molar volume at STP
Ÿ grams/mole = grams/L x 22.4 L/1 mole




Sample Problem 10.8 page 302 (Becky Hyatt)
Calculating the Molar Mass of a Gas at STP:
The density of a gaseous compound containing carbon and oxygen is found to be 1.964 g/L at STP. What is the molar mass of the compound?

1. Analyze- List the knowns and the unknown.

Ÿ knowns: density, mol (gas at STP)
Ÿ unknown: molar mass
Ÿ use conversion factor 22.4 L/1 mol

1. Calculate- Solve for the unknown.

Ÿ molar mass = …

1. Evaluate- Does the result make sense?

Ÿ the ratio of the calculated mass to the volume
Practice Problem:
A gaseous compound composed of sulfur and oxygen, which is linked to the formation of acid rain, has a density of 3.58 g/L at STP. What is the molar mass of this gas?

The Mole Road Map page 303 (Becky Hyatt)
Ÿ the mole is at the center of your chemical calculations
Ÿ to convert from one unit to another, you must use the mole as an intermediate step
Ÿ the form of the conversion factor depends on what you know and what you want to calculate








10.3 Percent Composition and Chemical Formulas

Haley Conatser (305) - Co-editor

Percent Composition

• The relative amounts of the elements in a compound are expressed as the percent composition or the percent by mass of each element in a compound.
• The percent composition of a compound consists of a percent value for each different element in the compound.
• The percent by mass of an element in a compound is the number of grams of the element divided by the mass in grams of the compound, multiplied by 100%

Click for a how-to and example

If you need another example.

Mike Hanley (305 - 306)

The Percent Composition of a Compound

• Knowing the relative amounts of the components of a mixture or compound can be very useful
• The relative amounts of the elements in a compound are expressed as the percent composition
• Percent Composition is the percent by the mass of each element in the compound
• The Percent composition of a compound consists of a percent value for each different element in the compound
• As an example, K2CrO4 can be used to show percent composition. The percent composition of it is K=40.3%, Cr=26.8%, and O=32.9%
• The percents MUST always add up to 100% (For example, in K2CrO4, 40.3% + 26.8% + 32.9% = 100%)
• Important Concept: The percent by mass of an element in a compound is the number of grams of the element divided by the mass in grams of the compound, multiplied by 100%

An Example of Percent Composition of The Earth's Air

Sample Problem:

When a 13.60 g sample of a compound containing only magnesium and oxygen is decomposed, 5.40 g of oxygen is obtained. What is the percent composition of this compound?

What you know...

• Mass of compound: 13.60g
• Mass of Oxygen: 5.40 g O
• Mass of Magnesium: 13.60g - 5.40g = 8.20g Mg
• The percent by mass of an element in a compound is the mass of that element divided by the mass of the compound multiplied by 100%.

Solving The Problem...

• %Mg= (Mass of Mg / Mass of Compound) X 100% = (8.20g / 13.60g) X 100% = 60.3%
• %O= (Mass of O / Mass of Compound) X 100% = (5.40g / 13.60g) X 100% = 39.7%

Answers...

• 60.3% Magnesium

• 39.7% Oxygen

Percent Compostition from the Chemical Formula

Andrea Luongo (307)

• You can calculate the percent composition of a compound if you know its chemical formula.
• Subscripts in the formula of the compound are used to calculate the mass of each element in a mole of that compound.
• The sum of these masses is the molar mass.
• By using the individual masses of each element and the molar mass you can calculate the percent of each element by molar mass and multiply by 100%.



EX.
Percent Mass:
Mass of the element compound in 1 mol x 100%
Molar Mass of Compound

• The percent composition of a compound is always the same.
• The percents of the elements add up to 100%.
• Use two significant figures.

EX.
Calculate the Percent Composition of Propane:

Mass of C in 1 molC3H8 = 36.0g
Mass of H in 1 molC3H8 = 8.0g
Molar Mass of C3H8 = 44.0g/mol

• Perecnt C = mass of C x 100%

mass of C3H8

• Percent C = 36.0g x 100%

44.0g

• Percent C = 81.8%



• Percent H = mass of H x 100%

mass of C3H8

• Percent H = 8.0g x 100%

44.0g

• Percent H = 18.0%


81.8 % + 18.0% = about 100%


TO SEE ANOTHER EXAMPLE OF PERCENT COMPOSITION VISIT:
http://www.youtube.com/watch?v=xbEeyT8nK84

Dan McCormack (308)

Percent Composition as a Conversion Factor

• Percent Composition is used to calculate the number of grams of any element in a specific mass of a compound.

  • Example Percent Composition ProblemCalculate the percent composition of carbon in each of the following:
  • CO2
  • Molar mass of compound:

• Mass due to carbon: 12.01 g/mol
• Percent composition of carbon:

James Payne (309-310)

Empirical Formulas

-Gives the lowest whole-number ratio of the atoms of the elements in a coumpound

-May or may not be the same as a molecular formula

Example:HO is empirical and H202 is the molecular

-The molecular formula tells the actual number of each kind of atom present

Mitch Martin (311)