Download Moles 2016

Moles 2016
Chemical
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What is a mole?
We sometimes use words to represent a specific number of items. The Mole
Examples: pair = 2
dozen = 12
gross = 144
a dozen dozen (12 x 12)
What is a mole?
mole to represent a really huge number.
Mole
In chemistry, we use the term 1 mole = 6.02 x 1023 particles 602,000,000,000,000,000,000,000 is a really big number! The reason why the number is so large is that we use it to count atoms and molecules. They are very tiny, so even in a small sample, there will be trillions and trillions of them. How did scientists come up with this number 6.02 x 1023 ? It started with the atomic masses for the elements. For example, carbon has an average atomic mass of 12.01 amu, meaning that one atom of carbon has a mass of 12.01 amu. The scientists wanted to be able to use the convenient atomic masses for the elements, but on a larger scale. So they decided to keep the numbers all the same, but just change the unit. Therefore, we get 12.01 grams of carbon. Same number, different unit. Grams instead of amu. We know that 1 atom of carbon is equal to 12.01 amu of carbon. But how many atoms of carbon are in 12.01 grams of carbon? This number was experimentally determined to be 6.02 x 10 23 atoms.
The number 6.02 x 10 23 is also known as Avogadro’s Number . It is named after Amadeo Avogadro, who is best known for his experiments with gases. 6.02 x 1023 particles = Avogadro’s Number = 1 mole
What this means is that the unit on every atomic mass on the periodic table can be changed from amu to grams, and that mass in grams will give you Avogadro’s number of that element. This is known as the molar mass because it is the mass (in grams) of one mole of that element. Moles 2016
Terms for Particles:
Particles could be atoms, molecules, formula units, ions, etc.
Atom: used to describe the individual particles of an element
Examples: He, Cu, S Molecule: used to describe the individual particles of a molecular Terms for Particles:
Particles could be atoms, molecules, formula units, ions, etc.
Formula Unit: used to describe the lowest ratio of the two ions in an ionic compound (metal or cation in the front)
Examples: NaCl, KNO3, Ag3PO4
compound (contains nonmetals/metalloids) or a diatomic element
Ions: are the ions in a chemical formula
Examples: CO2, PCl3, H2O (molecular compounds); H2, N2, O2, F2, Cl2, Br2, I2 (diatomic elements)
To remember the diatomics: I Bring Clay For Our New Hut
Ba3(PO4)2
Mole-Particle Conversions
In any reaction that we are performing, there are HUGE numbers of particles reacting. So we need a way to count these particles in groups. The unit mole does this for us. 1 mole = 6.02 x 10 23 particles “Moles” is abbreviated “mol”
You can see this on other resources as 6.022 X 10 23 It is helpful to group a sample of a certain chemical substance into moles because the number is more manageable using the unit mole. Conversion Practice
1. How many moles of copper are in 1.7 x 1024 atoms of copper?
Moles 2016
Conversion Practice
2.
How many atoms of gold are in 2.5 moles of gold?
Conversion Practice
4. How many formula units of sodium chloride are in 0.25 moles of sodium chloride?
Conversion Practice
3. How many moles of water are in 3.01 x 1023 molecules of water?
Mole-Mass Conversions
1 mole = molar mass in grams
How does the mole relate to mass?
To think about:
Does a dozen eggs have the same mass as a dozen cars?
Does a pair of shoes have the same mass as a pair of earrings?
0.25 moles NaCl 6.02 x 1023 formula units NaCl =
1 mole NaCl
1.5 x 1023 formula units A mole of helium does not have the same mass as a mole of carbon.
We call the mass of 1 mole of a substance its molar mass.
Where do we find the molar mass of an element?
Moles 2016
Conversion Practice
Mole-Mass Conversions
1 mole = molar mass in grams
Moles
Number of Particles
1 mole = molar mass in grams
1.
How many grams of silicon are in 5.0 moles of silicon?
2.
How many moles of potassium are in 136.9 g of potassium?
Molar Mass
Phosphorus 1 mole 6.02 x 1023 particles 30.97 g/mol
Aluminum
1 mole 6.02 x 1023 particles 26.98 g/mol
Silver
1 mole 6.02 x 1023 particles 107.87 g/mol
Now we can convert between grams and moles of a substance, by using the molar mass. Remember the main goal here is that we need to know how many particles (packaged in groups called moles) we have in a given amount of a substance. It’s important when we do chemical reactions. And we can’t count them by hand! But if we know the grams, we can convert to moles, and vice versa. Conversion Practice
Putting it all together
1 mole = 6.02 x 1023 particles
1 mole = molar mass
This concludes video 1. Be sure you took in­depth and high­quality notes. How many atoms of argon are in 87.6 g of argon?
Have good example problems in your notes.
What is the mass of 5.6 x 1024 atoms of aluminum?
What element do moles love to study in chemistry? Molybdenum
5.6 x 1024 atoms Al 1 mole Al 26.98 g Al = 250 g Al
6.02 x 1023 atoms Al 1 mole Al
Moles 2016
More on molar mass:
Conversion Practice
The molar mass of an element is easy to find. Just look on the Periodic Table!
But what if you have a compound ?
In that case, you add the molar masses of all the elements in the compound to get the molar mass for the compound. If the formula contains subscripts, you need to count that element the same number of times as the subscript. Example: H2O. Count H twice, O once.
1.
How many grams of ammonia are in 25.0 moles of ammonia?
Finding molar masses of compounds:
a. H2O
b. Ca(OH)2
2.
How many moles of silver nitrate are in 54.0 g of silver nitrate?
c. NH3
d. Al(NO3)3
1 (14.01) + 3(1.008) =17.03 g/mol NH3
Al 1 x 26.98 = 26.98
N 3 x 14.01 = 42.03
O 9 x 16.00 = + 144.00
213.01 g/mol Al(NO3)3
Mole-Volume Conversions
Conversion Practice
1 mole = 22.4 L
Avogadro discovered something special about gases and moles. At the same temperature and pressure, equal volumes of gases contain equal numbers of moles. For right now, we will just stick to the case of standard temperature and pressure, or STP. This is defined as 0 oC and 1 atmosphere of pressure. Under conditions of STP, 1 mole of ANY gas has a volume of 22.4 L. 1. How many moles of neon are in 44.8 L of neon at STP?
2. How many liters of CO2 gas are in 0.33 moles of CO 2 gas at STP?
Moles 2016
Conversion Practice
Putting it all together
1. How many molecules are in 45.6 g of carbon dioxide?
23
2. How many grams of calcium hydroxide are in 2.34 x 10
formula units of calcium hydroxide?
Conceptual Mole
Putting it all together
Wrapping up the idea of the mole:
1 mole= 6.02 x 1023 particles (atoms, molecules, ions, formula units, etc.)
1 mole = molar mass
1 mole = 22.4 L of any gas at STP
We can also relate moles to a chemical formula.
H2O 1 mole H2O = 2 moles H 1 mole H2O = 1 mole O
How many moles of Hydrogen are in 7.90 moles of water? 15.8 moles H 3. How many grams of helium gas are in 1.25 L of helium gas at STP?
Conceptual Mole
Putting it all together
We can also relate moles to ions.
This concludes video 2. Be sure you took in­depth and high­quality notes. Have good example problems in your notes.
How many moles of ions are 1 mole of Magnesium Chloride? How many moles of chloride ions are in 23.4 g of Magnesium Chloride?
How does Avogadro write to his friends? By e­mole!
Moles 2016
Mixed Mole Problems
When we are doing mole conversions, we need to identify whether the problem is: Mixed Mole Problems
When we are doing mole conversions, we need to identify whether the problem is: 22
1­step (requires only 1 conversion factor), or Example 1: How many grams are in 4.2 x 10
2­step (2 conversion factors). This is a two­step problem because “moles” is not in the question. You will start with atoms, convert to moles, and then convert from moles to grams.
• If the problem has the word “mole” in it (you are given moles or asked to find moles), you need 1 conversion factor (1 step) to solve it. atoms of iron?
4.2 x 1022 atoms Fe x 1 mole Fe x 55.85 g Fe = 3.9 g Fe
6.02 x 10 23 atoms Fe 1 mole Fe
• If the problem does not have the word “mole” in it, you need 2 conversion factors (2 steps) to solve it. You will have to go through moles in the middle of the problem.
Mixed Mole Problems
When we are doing mole conversions, we need to identify whether the problem is: Mixed Mole Problems
When we are doing mole conversions, we need to identify whether the problem is: Example 2: How many formula units are in 4.6 moles of NaCl?
Example 3: How many liters of CO2 gas at STP are in 43.0 grams of CO2 gas?
This is a one­step problem because you are given the number of moles. There is nothing new in this problem, just complete it the way you have been taught already. This is a two step problem because “moles” is not in the question. You will start with grams, convert to moles, and then convert from moles to liters.
4.60 mol NaCl x 6.02 x 1023 formula units NaCl = 2.77 x 1024 formula units NaCl
1 mole NaCl
43.0 grams CO2 x 1 mole CO2 x 22.4 L CO2 = 21.9 L CO2
44.01 g CO2 1 mole CO2
Moles 2016
Mixed Mole Practice
REMEMBER:
1 mole = 6.02 x 10 23 particles 1 mole = X grams (where X = molar mass)
1 mole = 22.4 L (for any gas at STP)
Mixed Mole Practice
REMEMBER: 1 mole = 6.02 x 1023 particles 1 mole = X grams (where X = molar mass)
1 mole = 22.4 L (for any gas at STP)
1. Find the number of moles in 25.0 g of NH4NO3.
2. What is the volume in liters of 1.15 x 10
28
molecules of oxygen gas (O2) at STP?
Mixed Mole Practice
REMEMBER: 6.02 x 10 23 particles = 1 mole
X grams = 1 mole (where X = molar mass)
22.4 L = 1 mole (for any gas at STP)
3. Find the number of liters in 7.55 mol N2 gas at STP.
4. Find the mass in grams of 8.45 x 10 25 atoms of copper.
Mixed Mole Practice
REMEMBER: 1 mole = 6.02 x 1023 particles 1 mole = X grams (where X = molar mass)
1 mole = 22.4 L (for any gas at STP)
5. Find the mass in grams of 150.0 L of helium gas at STP.
7. How many molecules are in 14.5 g of CCl4?
8. How many moles of lithium ions are in 3.54 moles of lithium oxide?
6. Find the number of moles in 3.35 x 1026 atoms of C.
Moles 2016
Percent Composition
This concludes extra video on mole practice. The percent composition of a compound is the mass percentages of all elements in the compound. Be sure you took in­depth and high­quality notes. Have good example problems in your notes.
Note: This is the same percentage you learned in math class.
%= part x 100
whole
You can find the percent composition of a compound if you are given its chemical formula, or if you are given the masses of all elements making up a sample of the compound. Examples:
1. Find the percent composition of magnesium chloride.
Percent Composition
Percent Composition
The percent composition of a compound is the mass percentages of all elements in the compound. The percent composition of a compound is the mass percentages of all elements in the compound. 2. Find the percent composition of aluminum in aluminum sulfate.
4. How many grams of calcium are in 45.6 g of calcium nitride?
Find percent calcium in Ca 3N2 and then use it to find the mass of Ca
3 (40.08 ) x 100 = 81.10% 0.8110 x 45.6 g Ca3N2 = 37.0 g Ca
3(40.08) + 2(14.01)
OR...dimensional analysis! 45.6 g Ca3N2 1 mole Ca3N2 3 mole Ca 40.08 g Ca = 37.0 g Ca
148.26 g Ca3N2 1 mole Ca3N2 1 mole Ca 3. How many grams of aluminum are in a 250. g sample of aluminum sulfate?
Moles 2016
Percent Composition
This concludes video 3. Be sure you took in­depth and high­quality notes. Let's look at hydrates with this in mind. 5. What is the percent of salt and the percentage of water in magnesium sulfate heptahydrate?
Have good example problems in your notes.
What was Avogadro's favorite board game? Moleoply!
Empirical Formula and
Molecular Formula
The molecular formula for a compound is its true formula, as it exists in nature.
The empirical formula for a compound is a reduced version of the molecular formula (simplest ratio of the elements). It is also known as “simplest formula.” Sometimes the empirical and molecular formulas are identical. Compound name
hydrogen peroxide
carbon dioxide
butane
iron (II) oxide
Molecular Formula Empirical Formula
Empirical Formula Calculations
Percent to mass,
Mass to mole,
Divide by small,
Multiply ‘til whole.
You can find the empirical formula for a compound if you have the masses or mass percentages of each element in the compound.
Steps in the process: 1) Obtain the mass of each element in the compound in grams. If percentages are given, just assume a 100 g sample and the masses will be equal to the percentages.
2)
Convert each element’s mass to moles using molar masses of the elements.
3)
Compare all mole amounts for the elements, and divide them all by the smallest one.
4) This usually leaves you with whole number ratios, which are the numbers of each element in the empirical formula. If you do not have whole numbers, multiply all numbers by some positive integer until they are all whole numbers.
5)
Write the empirical formula.
Moles 2016
Empirical Formula Calculations
POETRY
Here is a little “poem” to help you remember the steps for finding empirical formula:
Percent to mass,
Mass to mole,
Divide by small,
Multiply ‘til whole.
Empirical Formula Calculations
Percent to mass,
Mass to mole,
Divide by small,
Multiply ‘til whole.
Examples:
Examples:
1. Find the empirical formula for a compound that is 5.90% H and 94.10% S.
2. What is the empirical formula for a compound that is 25.90% N and 74.10% O?
Percent to mass,
Mass to mole,
Divide by small,
Multiply ‘til whole.
Molecular Formula Calculations
Empirical Formula Calculations
You can find the molecular formula for a compound if you have its empirical formula as well as its molar mass.
Examples:
Steps in the process:
3. 1)
Find the empirical formula if it is not given. (see previous section)
2)
Find the molar mass of the empirical formula.
25.0 g of a compound contains 6.64 g K, 8.84 g Cr, and 9.52 g O. Find its empirical formula. 3) Divide the molar mass of the molecular formula (always given) by the mass of the empirical formula. This will give you a whole number. 4) Multiply the empirical formula subscripts by this whole number to obtain the molecular formula.
Moles 2016
Molecular Formula Calculations
Molecular Formula Calculations
You can find the molecular formula for a compound if you have its empirical formula as well as its molar mass.
You can find the molecular formula for a compound if you have its empirical formula as well as its molar mass.
Examples:
Examples:
1. Find the molecular formula for a compound with empirical formula CH2 and molar mass 84 g/mol.
2. Find the molecular formula for a compound with empirical formula CH2O and molar mass 90 g/mol.
Molecular Formula Calculations
Molecular Formula Calculations
You can find the molecular formula for a compound if you have its empirical formula as well as its molar mass.
You can find the molecular formula for a compound if you have its empirical formula as well as its molar mass.
Examples:
Examples:
3. What is the molecular formula for a compound that is 40.0% C, 6.6% H, and 53.4% O. Its molar mass is 120 g. Hint: You have to find the empirical formula first! 4. Caffeine, a stimulant in coffee, tea, and sodas, has a molar mass 194.19 g/mol and percent composition 49.48% C, 5.19% H, 28.85% N, and 16.48% O. What is the molecular formula of caffeine?
49.48 g C 1 mole C = 4.1199 mol C = 4 So, empirical formula is C4H5N2O
12.01 g C
1.03
5.19 g H 1 mole H = 5.1488 mol H = 5 Molar mass of C4H5N2O is 97.1 g/mol
1.008 g H
1.03
194.19 = 2 97.1
28.85 g N 1 mole N = 2.0592 mol N = 2
14.01 g N
1.03
So, molecular formula is C8H10N4O2
16.48 g O 1 mole O = 1.03 mol O = 1
16.00 g O 1.03
Moles 2016
This concludes video 4. Be sure you took in­depth and high­quality notes. Have good example problems in your notes.
What are moles made of? Molecules!