|The MOLE ... and other Chemical Quantities
I. Quantitative Use of Chemical Formulas
A. Counting Atoms
___ _________ of H
___ _________ of O
___ atoms of K
___ atoms of Cr
___ atoms of O
___ atoms of Ca
____ atoms of O
____ atoms of H
CuSO4 . 5 H2O contains
____ atoms of Cu
____ atoms of S
____ atoms of H
____ atoms of O
B. Calculating the Formula Weight
________________ ______________ of a substance = the weight in amu of all the atoms in
a given formula
To calculate the FW (formula weight) of H2O
2 atoms H = 2 (
1 atom O = 1 (
) = ________________
Find the FW of K2Cr2O7
2 atoms K = 2 (
2 atoms Cr = 2 (
7 atoms O = 7 (
) = _____________
Find the FW of Ca(OH)2
1 atom Ca = 1 (
2 atoms O = 2 (
2 atoms H = 2 (
) = _______________
Find the FW of
c) HNO3 (aq) g) CuSO4 . 5 H2O
C. Using the Formula to find PERCENT COMPOSITION
______________________ - relative amounts of each element in a compound
To compute percent composition:
1) Find the FW (formula weight) of the compound
H = 2 ( 1.01 amu ) = 2.02 amu
O = 1 ( 16.00 amu ) = 16.00 amu
FW = 18.02 amu
2) Find the _____________________ of each element by:
% H = ______ X 100 =
% O = ______ X 100 =
3) Compute all percents to one decimal place then check to see if they total 100
D. Using the PERCENT COMPOSITION
Suppose you have a pile of __________ C6H12O6 with a mass of 28 g
What is the mass of C that is in that pile?
1) Find the FW of C6H12O6
C = (
H = (
O = (
) = ______________
2) Find the percent of C in C6H12O6
_______ ______ x 100 =
the percent is a ______________:
3) Use this conversion factor to solve the problem:
28 g C6H12O6
Example: What mass of glucose C6H12O6 will contain 50 g of Carbon?
1) Find the FW of glucose
2) Find the % composition of Carbon
3) Use the conversion factor, but make sure the units cancel !!
II. The MOLE
A. Defining the MOLE
1. IUPAC definition
The International Union of Pure and Applied Chemistry (IUPAC) defines the “mole”:
The mole is the amount of substance of a system which contains as many elementary particles
as there atoms in 0.012 kilogram (or 12 grams) of carbon-12.
In other words: in one _________ of carbon - 12, , there are __________________
carbon - 12 atoms
One mole of ANYTHING contains 6.02 x 1023 representative particles
In chemical terms:
______________________ = the smallest unit into which a substance can be broken down without a change in composition; the term refers to whether a substance commonly exists as atoms, ions, molecules
If the substance is an _______________________ (but, not a diatomic
element), RP = _________________
If the substance is a _______________________________, RP
If the substance is an ______________________________, RP =
2. Avogadro’s Experiment (1811)
By experimenting with gases, a scientist named ____________________ determined the
____________________ present in a given amount of an element:
1.01 gram sample of H
16.00 gram sample of O
Avogadro determined that there were _______________ atoms in each sample!
Conclusion of Avogadro's experiments:
Whenever you mass out the __________________ of an element, you will have
________________ atoms in the sample. This number is called
C. The MOLAR MASS
63.55 g Cu
32.06 g S
Each sample contains _____________________ atoms: this is called a
____________ of atoms
The ________________ ____________ of any element is the mass in grams of
1 mole of that element
What is the molar mass of the following elements?
18.02 g H2O
342.22 g C12H22O11
Each sample contains __________________________: this is a
______________ of molecules
The _______________ _______________ of a molecular compound is the
What is the molar mass of the following molecular compounds?
3. Formula Units
58.44 g NaCl
This sample contains _______________________: this is a
____________ of formula units
The __________________ ________________ of an ionic compound is the
What is the molar mass of the following ionic compounds?
. The _________________ of a substance is the mass in grams of one mole
. One mole contains 6.02 x 1023 representative particles
. The ____________ of a substance is the ________________ in
What is the representative particle in a:
a) bowl of
e) crucible of magnesium oxide
b) shaker of
f) air bag full of nitrogen gas
c) bottle of
g) Neon sign
d) He filled
h) copper pipe
C. Mole Conversions
1. Given Moles, Convert to Grams
There are three steps to converting moles of a substance to grams:
1. Determine how many moles are given in the problem.
2. Calculate the molar mass of the substance.
3. Using dimensional analysis: Multiply step one by step two.
Example: A laboratory procedure needs 0.10 moles of Mg
ribbon. How much Mg
ribbon should you use?
Calculate how many grams are in 0.700 moles of H2O2
Convert 2.50 moles of KClO3 to grams
2. Given Grams, Convert to Moles
1) Determine how many grams are given in the problem.
2) Calculate the molar mass of the substance.
3) Use dimensional analysis to setup solution.
Example: A jug of distilled water contains one liter or 1000.0
How many moles is this?
Convert 25.0 grams of KMnO4 to moles
Calculate how many moles are in 17.0 grams of H2O2
3. How many Representative Particles (Atoms or Molecules or Formula Units) ?
how many moles are given in the problem.
the relationship: 6.02 x 1023 representative
particles = 1 mole
dimensional analysis to setup the problem.
Example: Propane (C3H8)
is a gas used for cooking and heating.
molecules are in
2.12 mol of propane?
How many moles is 2.80 x 1024
How many moles is 2.17 x 1023
III. Using the Percent Composition to find the EMPIRICAL
FORMULA and the MOLECULAR FORMULA
A. Finding the Empirical Formula
_________________ - lowest whole number ratio of the atoms of the elements in a compound
. the subscripts: ________ for H tell us the ___________ of atoms in one molecule
________ for S
_____ atoms H : _____ atom S
. in a larger sample: more atoms are present, but still in a ____ :
50,000 atoms H : ______________ atoms S
or ______________ atoms H : 6.02 x 1023 atoms S
. using the mole: the ____________ equals the
the _____________ in the formula
To find the Formula (subscripts) of a compound:
1) Convert the _____________ of each element present to __________
2) Change the moles to a _______________: ___________________________
3) Use this mole ratio as the ____________________ in the formula
Example: A compound contains 40.0 g of C, 6.70 g of H and 53.30 g of O. Find the empirical formula.
Example: A compound contains 1.10 g of Cr and .51 g of O. Find its formula.
Example: A compound contains 43.6% P and 56.4% O. Find its formula.
The data is given in percents! Assume you have a 100 g sample and convert the percents to grams.
B. Find the MOLECULAR FORMULA
_______________ - a chemical formula that shows the actual number and kinds of atoms present in a molecule of a compound
. many molecules contain a ratio of atoms that is some multiple of the empirical formula
. for example, butane molecules are C4H10 not C2H5
. to find the true formula: 1) find the empirical formula 2) need the mass of the actual formula (Formula Weight)