formula stoichiometry. what is stoichiometry? deals with the specifics of quantity in chemical...
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Formula StoichiometryFormula Stoichiometry
What is What is stoichiometrystoichiometry??
Deals with the specifics of QUANTITY Deals with the specifics of QUANTITY in chemical formula or chemical in chemical formula or chemical reaction.reaction.
Review: Counting Atoms Review: Counting Atoms
Remember Remember subscriptssubscripts tell you how tell you how many atoms…many atoms…
… … CoefficientsCoefficients tell you how many tell you how many TOTAL molecules compoundsTOTAL molecules compounds
How many oxygen atoms in each?How many oxygen atoms in each?
NHNH44NONO33
CC88HH88OO4 4
OO33
CC33HH55(NO(NO33))33
(3)
(4)
(3)
(9)
Counting Atoms PracticeCounting Atoms Practice
(NH(NH44))22COCO33
N:
H:
C:
O:
* First list the types of atoms and then count each.
Example #1:
2
8
1
3
Counting Atoms PracticeCounting Atoms Practice
CaCrOCaCrO44
Ca:
Cr:
O:
* First list the types of atoms and then count each.
Example #2:
1
1
4
Counting Atoms PracticeCounting Atoms Practice
CaCa33(PO(PO44))22
Ca:
P:
O:
* First list the types of atoms and then count each.
Example #3:
3
2
8
**Do the rest on your own!**
Atomic MassAtomic Mass
Mass of an atom of one element Mass of an atom of one element based on based on percent abundances and percent abundances and masses of all isotopes (on PT)masses of all isotopes (on PT)
Units: amuUnits: amu
Molecular MassMolecular Mass
Mass of a Mass of a molecular compound (ex: molecular compound (ex: HH22O, COO, CO22))
Units: amuUnits: amu
Formula MassFormula Mass
Mass of an Mass of an ionic compound (ex: NaCl, ionic compound (ex: NaCl, MgIMgI22))
Units: amuUnits: amu
Gram Formula MassGram Formula Mass
Mass expressed in gramsMass expressed in grams
Gram Molecular MassGram Molecular Mass
H2O
=O H + H
+ +
+
Molecular Mass = 15.9994 amu + 1.00794 amu +1.00794 amu
Gram Molecular Mass = 18.0 g
How do I calculate molecular or How do I calculate molecular or formula mass?formula mass?
First:First: Identify and count atoms in the Identify and count atoms in the compound.compound.
Second:Second: Locate atomic mass of each Locate atomic mass of each element.element.
Third:Third: Multiply mass x number of Multiply mass x number of atoms and total all elements.atoms and total all elements.
Molecular Mass Example Molecular Mass Example (Covalent Compound)(Covalent Compound)
Example: HExample: H22OO H- 2 x 1H- 2 x 1 O- 1 x 16O- 1 x 16 Molecular Mass = 18 gMolecular Mass = 18 g
Formula Mass Example Formula Mass Example (ionic compound)(ionic compound)
Example: NaClExample: NaCl Na- 1 x 23Na- 1 x 23 Cl- 1 x 35.5Cl- 1 x 35.5 Formula Mass = 58.5 gFormula Mass = 58.5 g
Percent Composition by MassPercent Composition by Mass
Experimentally-Experimentally- Use masses given in problemUse masses given in problem
Mass of ElementMass of Element x 100 x 100
Mass of CompoundMass of Compound
Example:Example:
A compound containing carbon and A compound containing carbon and hydrogen has a mass of 16 grams. hydrogen has a mass of 16 grams. When decomposed, 12.0 grams are When decomposed, 12.0 grams are found to be carbon. What is the found to be carbon. What is the percent by mass of carbon in the percent by mass of carbon in the compound? compound?
Theoretically-Theoretically- Use Atomic MassesUse Atomic Masses FormulaFormula
(#atoms of element) x (atomic mass)(#atoms of element) x (atomic mass) x100 x100
Formula mass of compoundFormula mass of compound
Percent Composition by Atomic Percent Composition by Atomic MassMass
Hydrated CrystalsHydrated Crystals
Some ionic compounds are found to have Some ionic compounds are found to have surrounding water molecules.surrounding water molecules.
These compounds are called These compounds are called Hydrated Hydrated CrystalsCrystals..
The The percent water hydration percent water hydration can be can be found.found.
ExampleExample
CuSOCuSO44 .. 5H5H22OO
The dot shows that The dot shows that 5 H5 H22O molecules are O molecules are attached to 1 CuSOattached to 1 CuSO4 4 moleculemolecule. .
Percent Water HydrationPercent Water Hydration
% Hydration = % Hydration = Total mass of WaterTotal mass of Water x 100 x 100
Formula MassFormula Mass
CuSOCuSO44 .. 5H 5H22OO
Cu – 1 x 63.5 = 63.5Cu – 1 x 63.5 = 63.5
S – 1 x 32 = 32S – 1 x 32 = 32
O – 4 x 16 = 64O – 4 x 16 = 64
HH22O – 5 x 18 = 90O – 5 x 18 = 90
Formula Mass = 249.5Formula Mass = 249.5
% Hydration = (90/249.5) x 100% Hydration = (90/249.5) x 100
= 36% H= 36% H22OO
The MoleThe Mole
Avagadro’s NumberAvagadro’s Number is the number is the number of atoms in of atoms in 1 mole1 mole of any substance. of any substance.
Avagadro’s Number is 6.02 x 10Avagadro’s Number is 6.02 x 102323
That means that in 1 mole of any That means that in 1 mole of any sample of matter there are 6.02x10sample of matter there are 6.02x102323 particles.particles.
The MoleThe Mole There are 6.02 x 10There are 6.02 x 102323 particlesparticles in one in one
molemole of any substance of any substance
One particle can be one One particle can be one atomatom or one or one moleculemolecule..
The mass of 1 mole will be different for all The mass of 1 mole will be different for all substances.substances.
Atomic / Formula / Molecular Mass = Atomic / Formula / Molecular Mass = Molar MassMolar Mass because it is the mass of 1 because it is the mass of 1 mole of any substance.mole of any substance.
Example: Example: 1 mole of H1 mole of H22O = 18gO = 18g
Mole Relationships or EqualitiesMole Relationships or Equalities 1 mole = formula mass in grams1 mole = formula mass in grams
1 mole = 6.02 x 101 mole = 6.02 x 102323 particles particles
1 mole = 22.4L (for gases)1 mole = 22.4L (for gases)
Formula mass = 6.02x10Formula mass = 6.02x102323 particles particles
22.4L of a gas = 6.02x1022.4L of a gas = 6.02x102323 particles particles
Formula mass = 22.4L of a gasFormula mass = 22.4L of a gas
Example ConversionsExample ConversionsConverting Grams to Moles
given grams XGFM
1 moles
grams
Converting Moles to Grams
given moles Xmoles
grams
1
GFM
Table TTable T For problems that involve mass mole For problems that involve mass mole
conversions you can use the “Mole conversions you can use the “Mole Calculation” formula on Table T.Calculation” formula on Table T.
You will usually have to calculate the You will usually have to calculate the gram formula mass of the substance gram formula mass of the substance unless it is given.unless it is given.
See Table TSee Table T
ExamplesExamples
Example #1: What is the mass of 1.75 Example #1: What is the mass of 1.75 moles of oxygen gas (Hint: oxygen is moles of oxygen gas (Hint: oxygen is diatomic)?diatomic)?
1st find the molecular mass of oxygen remember oxygen is a diatomic element (O2).
O: 2 x 16 g= 32 g
Convert from moles to grams using factor label method
Factor Label Setup
1.75 mol x __32 g _ = ? g
1 mol
56 g
ExamplesExamples
Example #2: How many moles are in Example #2: How many moles are in 42 g of water?42 g of water?
1st find the molecular mass of H2O.
H: 2 x 1 = 2
O: 1 x 16 = 16
2 + 16 = _18 g_
1 mol
Convert from grams to moles…
42 g x __ 1 mol _ = ? mol
18 g
2.3 mol
ExamplesExamplesExample #3: How many moles of Example #3: How many moles of
potassium chromate are in a 500 g potassium chromate are in a 500 g sample?sample?
1st find the molecular mass of potassium dichromate (K2CrO4).
K:2 x 39 = 78
Cr: 1 x 52 = 52
O: 4 x 16 = 64
78+104+112 = _194 g_
1 mol
Convert from grams to moles…
500 g x __ 1 mol _ = ? mol
194 g
2.6 mol
Empirical MassEmpirical Mass
Step 1: CHStep 1: CH22O Empirical MassO Empirical Mass
C – 1 x 12 = 12C – 1 x 12 = 12
H – 2 x 1 = 2H – 2 x 1 = 2
O – 1 x 16 = O – 1 x 16 = 1616
3030
Step 2: Calculate Multiple (Formula Step 2: Calculate Multiple (Formula mass/Empirical mass)mass/Empirical mass)
180/30 = 6180/30 = 6
Step 3: Multiply Empirical Formula by Step 3: Multiply Empirical Formula by Multiple Multiple
6(CH6(CH22O) = CO) = C66HH1212OO66