Name: ________________________________________
Chapter 10: MOLAR MASS AND PERCENT COMPOSTION
http://youtu.be/Qflq48Foh2w
MOLAR MASS OF COMPOUNDS
What is the molar mass of a substance?
The molar mass of a substance is the mass (in grams) of 1 mole of that substance
(or, the mass of 6.02 X 1023 particles of that substance)
REVIEW:
What is the molar mass of the element Carbon?
What is the molar mass of Nitrogen gas?
To calculate MOLAR MASS of a compound…..
1. Write the formula of the compound from the name
1. Find atomic mass of each element
2. MULTIPLY each atomic mass by the appropriate subscripts
3. ADD (units are g/mole) (the amount of grams in one mole)
EXAMPLES:
Find molar mass of water.
2 mol H 
1 mol O 
FORMULA
2(1.01g/mol) =
1(16.00g/mol) =
H2 O
2.02g/mol
16.00g/mol
18.02g/mol
So, the Molar Mass of H2O = 18.02 g/mol
You Try: Find molar mass of sulfuric acid
FORMULA
H2SO4
2 mol H 
1 mol S 
4 mol O 
For ionic compounds, reminder to criss cross in order to find the chemical formula.
1
Hydroxide is a poly!!!!
Use parentheses for poly’s
Record your masses to the hundredth’s place!!!!
Do 1st
1. sodium hydroxide
1st write the formula by crisscross   
SCRAPWORK
nd
2 add up the molar mass very neatly!
FORMULA: __NaOH_____
Na+1 (OH)-1
YOU TRY IT
Na: 1 ( 22.98) = 22.99
O: 1 ( 16.00) = 16.00
NaOH
40.0 g/mol
H: 1 ( 1.01) = 1.01
2. magnesium hydroxide
1st write the formula by crisscross
2nd add up the molar mass very neatly!
FORMULA: __ Mg(OH)2 ______
Mg: 1 ( 24.31) = 24.31
O: 2 ( 16.00) = 32.00
Mg+2 (OH)-1
Mg(OH)2
58.47 g/mol
H: 2 ( 1.01) = 2.02
3. calcium cyanide
1st write the formula by crisscross
nd
2 add up the molar mass very neatly!
FORMULA: _____________
4. magnesium phosphate
1st write the formula by crisscross
nd
2 add up the molar mass very neatly!
FORMULA: _____________
5.
iron(III) dichromate
1st write the formula by crisscross
2nd add up the molar mass very neatly!
FORMULA: _____________
6.
ammonium hydroxide
1st write the formula by crisscross
nd
2 add up the molar mass very neatly!
FORMULA: _____________
7. dinitrogen pentoxide
covalent so don’t criss cross
nd
2 add up the molar mass very neatly!
FORMULA: _____________
2
PER CENT COMPOSITION OF AN ELEMENT IN A COMPOUND
http://youtu.be/lywmGCfIUIA
To calculate PERCENT COMPOSITION…….
1. Write the formula of the compound
2. Find the molar mass of the each element
3. Find the TOTAL MOLAR MASS of the compound
4. DIVIDE the molar mass of each element by
TOTAL MOLAR MASS of the compound.
5. MULTIPLY each by 100 to find percent of each
Find percent composition of C2H6O
EXAMPLES:
FORMULA: ____ Ca(CN)2______
1ST -Find molar mass NEATLY
Ca – 1 x 40.08g = 40.08g
C2 – 2 x 12.01 g = 24.02g
N2 – 2 x 14.01g = 28.02g
2ND percent  (PART/WHOLE)(100) = %
% Ca = _(40.08/92.12) x 100 = 43.51%
% C = _(24.02/92.12) x 100 = 26.07%
% N = _(28.02/92.12) x 100 = 30.41%
92.12 g/mole
From per cent composition, we can determine the mass of an element in a given sample of that
compound:
How many grams of calcium are in 40.0g of calcium cyanide?
Formula to use = [(percent (in decimal) of Ca in Compound)(40.0 g of the compound)]
% Ca = 43.51%  in decimal it is 0.4351

[(0.4351)(40.0g) = 17.4g of Ca
a. Find the per cent composition of magnesium phosphate:
FORMULA: ______________________
% Mg = __________
% P = __________
% O = __________
How many grams of magnesium are in 350g of magnesium phosphate?
3
***** Extension: From percent composition, we can determine the mass of a given sample of that
compound if we know the mass of an element in that sample:
What mass of magnesium phosphate contains 15g of magnesium?
YOU TRY SOME:
1.
Find the molar mass of each compound (review):
a. lithium carbonate
____________________
b.
calcium nitrate
_____________________
c.
tin (IV) sulfate
______________________
2. Find the percent composition of tin (IV) sulfate.
% Sn = __________
% S = __________
% O = __________
How many grams of tin are in 250g of tin (IV) sulfate?
4
MOLE CONVERSIONS Moles/Mass, Moles/Particles, Moles/Volume
1. mole grams http://youtu.be/CMnkSb2YsXI
2. mole grams http://youtu.be/0RXB8xNmJNM
3. mole particles http://youtu.be/HMAOrGpkTsQ
4. mole particles http://youtu.be/kGNtnq0kGKk
5. mole liters http://youtu.be/Y8e7T09SKZ0
Mass
Mole
1 mole O2
32.00g O2
Volume
Mole
(at STP)
1 mole O2
22.4 liters O2
Particles
Mole
1 mole O2
6.02 x 1023 molecules O2
1 mole CO2
44.01g CO2
1 mole CO2
22.4 liters CO2
1 mole He
6.02 x 1023 atoms of He
4.00g He
1 mole He
22.4 liters O2
1 mole O2
6.02 x 1023 formula units NaCl
1 mole NaCl
180.00g C6H12O6
1 mole C6H12O6
22.4 liters CO2
1 mole CO2
6.02 x 1023 Br- ions
1 mole Br- ions
5
MOLE/MASS and MASS/MOLE/PARTICLE CONVERSIONS USING MOLAR MASS
STEP 1: Write the correct formula
STEP 2: Determine the molar mass
STEP 3: Use dimensional analysis to convert
Conversion Factors
1 mole = 6.02 x 1023 molecules
1 mole = 6.02 x 1023 formula units
1 mole = 6.02 x 1023 atoms
1 mole = molar mass in grams
EXAMPLES:
1. Find the mass of 4.50moles of diphosphorus pentoxide.
2nd – Set up the bridge to convert moles into mass (grams)
4.50 mol P2O5 x 141.94 g mol P2O5 = 639 g P2O5
1 mol P2O5
1st – Write the formula. If it is covalent , then don’t criss
cross. If it is ionic, then criss cross. Then add up molar mass
P2O5
2(30.97) + 5(16.00)= 141.94 g. (this goes near the gram in the
conversion factor.
___639 g P2O5_
2. How many moles is 250.0g of copper (II) sulfate?
2nd – Set up the bridge to convert mgrams into moles
250.0 g CuSO4 x 1 mol CuSO4 = 1.57 mol CuSO4
159.57 g CuSO4
3. Find the mass of 0.545moles of calcium cyanide.
1st – Write the formula. If it is covalent , then don’t criss
cross. If it is ionic, then criss cross. Then add up molar mass
Cu+2 (SO4)-2 (charges wipe out)
CuSO4
1(63.5) + 1(32.07) + 4(16.00)= 159.57 g. (this goes near the
gram in the conversion factor.
___1.57 mol CuSO4___
4. How many molecules are in 110g of diphosphorus pentoxide? _______________
(Hint: go through the mole)
YOU TRY SOME:
1.
575g of sodium sulfate to moles
________________
2.
0.025moles of phosphorus pentachloride to grams
________________
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3.
15.0g of iron(III) nitrate to moles
________________
4.
8.02 x 1023 molecules of carbon disulfide to grams
________________
MOLES AND VOLUME OF MATTER
Avogadro’s Hypothesis:
STP:
How many is a mole?
1 mole = 6.02 X 1023 atoms, molecules, formula units, or particles
How heavy is a mole?
1 mole = molar mass in grams
How much space does a mole occupy?
1 mole = 22.4 L (for a gas at STP)
YOU TRY SOME-Make the following mole conversions:
a.
14.0L of nitrogen gas at STP to moles
b.
2.5g of chlorine gas at STP to molecules
c.
2.24 x 1025 atoms of neon at STP to liters
d.
13.3L of fluorine gas at STP to grams
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EMPIRICAL AND MOLECULAR FORMULAS http://youtu.be/wnRaBWvhYKY?list=PL3hPm0ZdYhyyWLwHs-N8En7iTuJ9jZQqr
http://youtu.be/ucU5PD6W3Ik?list=PL3hPm0ZdYhyyWLwHs-N8En7iTuJ9jZQqr
http://youtu.be/J_MtVs0aBdU?list=PL3hPm0ZdYhyyWLwHs-N8En7iTuJ9jZQqr
Compare the Empirical Formula and Molecular Formula of each compound above.
What is an Empirical Formula?_______________________________________________________________
What is a Molecular Formula?_______________________________________________________________
YOU TRY SOME: Given the following molecular formulas, determine the empirical formula of each
compound.
a. P4O10
b. C6H12O6
__________
_________
c. C3H6O
________
http://youtu.be/lyWAGMEKzSY
If we know the empirical formula and the molar mass of a compound, we can determine the molecular
formula of that compound by finding the ratio of the given molecular molar mass to the molar mass of the
empirical formula.
For example: Given the empirical formula CH and the molar mass 78g/mol, find the molecular formula.
STEP 1: Find molar mass of the empirical formula: 12 g/mol + 1 g/mol = 13 g/mol
STEP 2: Divide the given molecular molar mass by the empirical molar mass (from step 1): 78 g/mol = 6
13 g/mol
STEP 3: Round your answer in Step 2 to the nearest whole number (this is the ratio): 6
STEP 4: Multiply all subscripts in the empirical formula by the ratio from step 3: C6H6
http://youtu.be/IYDTbqg5IG4
8
These are easier than the video since the empirical formula is given in these next few problems:
Determine the molecular formula of each compound
1.
The empirical formula of a compound is CH2O. Its molar mass is 360g/mol. Find its molecular
formula.
2.
The empirical formula of a compound is P2O5. Its molar mass is 284g/mol. Find its molecular formula.
3. The empirical formula of a compound is CH2O. Its molar mass is 180g/mol. Find its molecular formula.
4. The empirical formula of a compound is HO . Its molar mass is 34g/mol. Find its molecular formula.
HW#1: REVIEW- NAMING AND MOLE CONVERSIONS
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NAME
Ionic or Covalent?
FORMULA
Potassium permanganate
Tricarbon octahydride
Iron (III) carbonate
Tetraphosphorus decoxide
Aluminum sulfate
Copper (II) sulfite
Magnesium iodide
Tetraphosphorus decoxide
Mole conversions: (you may want to go back and look at your previous notes on mole conversions)
a. Find the mass of 1.25 moles of K (mole → g)
b. How many moles is 2.50g of oxygen? (hint: oxygen is diatomic) (g → mole)
c. Find the number of atoms in 5.45 g of phosphorus. (g → mole → atoms)
HW #2 MOLAR MASS/ PER CENT COMPOSITION
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1. Label each compound below as ionic or molecular. Write the formula and determine the molar mass
of each compound.
COMPOUND
IONIC/
FORMULA
MOLECULAR?
MOLAR MASS
barium sulfate
tricarbon octahydride
iron (III) carbonate
tetraphosphorus
decoxide
strontium phosphate
2. Find the per cent composition of iron (III) carbonate.
% Fe =
%C=
%O=
How many grams of iron are in 125g of iron (III) carbonate?
What mass of iron(III) carbonate contains 10.0g of iron?
HW #3 PERCENT COMPOSITION
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Determine the percent composition of each of the compounds below:
1. KMnO4
% K = ______________
% Mn = _____________
% O = ______________
2. HCl
% H = ______________
% Cl = ______________
3. Mg(NO3)2
% Mg = _____________
% N = ______________
% O = ______________
4. (NH4)3PO4
% N = _____________
% H = ______________
% P = ______________
% O = ______________
5. Al2(SO4)3
% Al = ______________
% S = ______________
% O = ______________
Solve the following problems:
6. How many grams of oxygen can be produced from the decomposition of 100g of KClO3?
7. How much iron can be recovered from 25.0g of Fe2O3?
8. How much silver can be produced from 125g of Ag2S?
HW #4 CONVERSION PRACTICE
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1. Write the formula for each compound below. Then determine its molar mass.
FORMULA
MOLAR MASS
a. calcium sulfate
b. aluminum cyanide
c. phosphorus triiodide
2. Use the molar masses you found in Part 1 to make the following conversions:
a. Find the mass of 1.25moles of calcium sulfate.
b. How many moles is 2.50g of aluminum cyanide?
c. Find the mass of 0.750moles of phosphorus triiodide.
d. How many molecules is 12.50g of phosphorus triiodide
e. Find the number of formula units in 10.0g of calcium sulfate.
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HW #5 MIXED MOLE CONVERSION PRACTICE
1.
Convert the quantities below to moles:
a.
14.0g of lead
_____________________
b.
20.5g of lithium hydroxide
______________________
c.
14.0L of oxygen gas at STP
_______________________
d.
15.0g of calcium nitrate
_______________________
2. Find the mass of:
a.
10.0L of hydrogen gas at STP
_______________________
b.
4.5 moles of sodium sulfate
_______________________
c.
3.21 x 1022 molecules of carbon tetrachloride
_______________________
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PER CENT SUGAR IN BUBBLE GUM
NAME:
DATE:
PERIOD:
BACKGROUND: In this lab you are going to design and carry out an experiment to determine the percentage
of sugar in bubble gum. To do so, you will assume that all of the flavoring removed from bubble gum during
chewing is sugar. The chemical formula for sucrose, the sugar in bubble gum, is C12H22O11. After determining
the percentage of sugar in bubble gum, you will then determine the mass of carbon and the number of carbon
atoms in the sugar in a piece of bubble gum.
PROCEDURE: Write out the procedure (in words) you will follow in the space below. Include all
details.
1.__________________________________________________________________________________
2.__________________________________________________________________________________
3. .__________________________________________________________________________________
4. .__________________________________________________________________________________
5.
DATA: Set up a data table in the space below to record all necessary data.
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CALCULATIONS: Show and explain all work. Calculations must be neat and easy to follow.
a. mass of sugar in your piece of gum: (show calculation!)
a.
% sugar in bubble gum [% = (part/whole) x 100) ]
(show calculation based on your data!)
b.
% carbon in sugar (C12H22O11) (show calculation – use your class notes on % composition)
c.
mass of carbon in the sugar in your piece of bubble gum (show calculation, use class notes)
(HINT: What per cent of sugar is carbon? How many grams of sugar were in your gum? )
d. Find the # of atoms of carbon from the grams you calculated in “d”. (use dimensional analysis)
CONCLUSIONS:
1. What did you learn from this experiment?
2. List two sources of error and describe the effect each had on your results. (Would the error make the per
cent sugar reported too high or too low and why).
a.
b.
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HYDRATES
A hydrate has H20 molecules attached to the solid form. If
we heat a hydrate, we can drive off the water
(and be left with the dry anhydrous form).
The following information is obtained in a CuSO4 • X H2O hydrate lab:
22.00g: mass of the crucible and cover
24.50g: mass of crucible, cover, and hydrate
23.59g: mass of crucible, cover, and anhydrous powder
1) Find the mass of hydrate
2) Find the mass of anhydrous powder.
3) Find the mass of the water driven off.
4) Find the empirical formula of the hydrate.
17