HONORS CHEMISTRY
CLACULATING FORMULA WEIGHT
(MOLAR MASS)
NAME ____________________________________________
4-15-14
I CAN _____________________________________________________________________________________________________________
____________________________________________________________________________________________________________________
A PRACTICAL UNIT TO MEASURE THE MASS OF ATOMS
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We’ve talked about the mass of atoms in terms of one or two….but these masses are very
small.
To be practical for __________________________________, a standard of measure had to be
_________________________ so that ________________________________________________________________.
To that end, scientists created a unit called the _______________________________________________ used
to measure the mass of subatomic particles.
AVAGADRO’S NUMBER
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The __________________________________________ was assigned a value of ________________________________
(________).
To create a system of practical measurement, scientists used the atom ____________________________
[6 P+ and 6 No] and assigned it a mass of _____________________________.
Then they calculated the ________________________________________________ to make a
________________________________________________________________________.
They found it took _______________________________________________ of C-12 to have a mass of 12
grams. In turn, each element’s atomic mass required ________________________________________ to
equal the same mass in grams.
FOR EXAMPLE
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_______________of Oxygen 16 has a mass of ________________________ .
_______________________________________________of O-16 has a mass of ______________________________!
This number became very important in chemistry is known as:
__________________________________________________
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The quantity of matter containing Avagadro’s Number of particles, such as
______________________________________________________________________________ is known as a:
__________________________
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When working in a lab setting, the __________________ is used to determine quantities of
chemicals.
MASS CALCULATIONS AND CHEMICAL FORMULAS
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Chemical Formulas represent the ________________________ and the ___________________________________
of each that compose a compound.
– Subscripts in formulas relate to the element immediately _________________________ of them.
– If a formula contains a _______________________________ followed by a subscript, the subscript
_________________________________________________________.
EXAMPLE
CALCULATING FORMULA WEIGHT (MOLAR MASS)
_______________________________________ (____________________________) of an element or compound is the
________________________________________________________________________of the element or compound.
For an ______________________, the FW is the ________________________________________________________, or
for a _______________________________________________.
For a ______________________________, the FW is found by counting the ________________________________
____________________________________________________________.
__________________________ the _____________________________ X the ____________________________________ of
the element (from the PT).
___________________________________________ and ___________________________________________.
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EXAMPLE
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What is the formula weight of Calcium Carbonate?
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Formula for Calcium Carbonate is: ____________________________
HYDRATES
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Certain ionic compounds trap water molecules in their structure when they form.
These are known as _____________________________.
Hydrates are written in this manner:
Compound Formula Dot Number of Water Molecules
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Hydrates are named as:
_______________________________________, a ___________________ for the number of water molecules, then
the word ____________________________.
When calculating the formula weight of a hydrate, just include the _______________________________
______________________________________________________________ in the total.
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PRACTICE PROBLEM
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What would be the formula weight of Magnesium Chlorate Pentahydrate?
Formula =
PRACTICE PROBLEMS
Complete the following FORMULA WEIGHT (MOLAR MASS) calculations ON YOUR OWN PAPER!
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1. Find the FORMULA WEIGHT of Aluminum Sulfate, Al2(SO4)3.
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2. What is the MOLAR MASS of Glucose, C6H12O6?
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3. Find the FORMULA WEIGHT of:
Sodium Potassium Permanganate Tetrahydrate,
NaK(MnO4)2  4H2O ?
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4. What is the MOLAR MASS of Ammonium Phosphate Dihydrate?