The MOLE ... and other Chemical Quantities
I. Quantitative Use of Chemical Formulas
A. Counting Atoms
H_{2}O
contains
___ _________ of H
___ _________ of O
K_{2}Cr_{2}O_{7 }
contains
___ atoms of K
___ atoms of Cr
___ atoms of O
Ca(OH)_{2} contains
___ atoms of Ca
____ atoms of O
____ atoms of H
CuSO_{4 } ^{ .} 5 H_{2}O 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 H_{2}O
2 atoms H = 2 (
) =
1 atom O = 1 (
) = ________________
FW =
Find the FW of K_{2}Cr_{2}O_{7}
2 atoms K = 2 (
) =
2 atoms Cr = 2 (
) =
7 atoms O = 7 (
) = _____________
FW =
Find the FW of Ca(OH)_{2}
1 atom Ca = 1 (
) =
2 atoms O = 2 (
) =
2 atoms H = 2 (
) = _______________
FW =
Find the FW of
a) N_{2}O_{4}
e) C_{12}H_{22}O_{11}
b) MgBr_{2 }
f) Fe_{2}(Cr_{2}O_{7})_{3}
c) HNO_{3} _{(aq)} g) CuSO_{4} ^{ . } 5 H_{2}O
d) Ca_{3}(PO_{4})_{2 }
h) KCl
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
ex. H_{2}O
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 __________ C_{6}H_{12}O_{6} with a mass of 28 g
What is the mass of C that is in that pile?
1) Find the FW of C_{6}H_{12}O_{6}
C = (
) =
H = (
) =
O = (
) = ______________
2) Find the percent of C in C_{6}H_{12}O_{6}
% =
_______ ______ x 100 =
the percent is a ______________:
3) Use this conversion factor to solve the problem:
28 g C_{6}H_{12}O_{6}
Example: What mass of glucose C_{6}H_{12}O_{6} 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 carbon12.
In other words: in one _________ of carbon  12, , there are __________________
carbon  12 atoms
One mole of ANYTHING contains 6.02 x 10^{23} 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 =
________________________
Examples:
Substance
Representative particle
water
magnesium
salt
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
1. Atoms
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
Units:
What is the molar mass of the following elements?
a)
copper
d) sodium
b)
sulfur
e) carbon
c) magnesium
2. Molecules
18.02 g H_{2}O
342.22 g C_{12}H_{22}O_{11}
Each sample contains __________________________: this is a
______________ of molecules
The _______________ _______________ of a molecular compound is the
_______________
Units:
What is the molar mass of the following molecular compounds?
a) NH_{3}
b) CO_{2}
c) Cl_{2}
d) C_{6}H_{12}O_{6}
3. Formula Units
58.44 g NaCl
This sample contains _______________________: this is a
____________ of formula units
The __________________ ________________ of an ionic compound is the
____________________
Units:
What is the molar mass of the following ionic compounds?
a) MgO
b) CaCl_{2}
c) Mg(OH)_{2}
d) Al(NO_{3})_{3}
. The _________________ of a substance is the mass in grams of one mole
. One mole contains 6.02 x 10^{23} representative particles
. The ____________ of a substance is the ________________ in
What is the representative particle in a:
a) bowl of
sugar
e) crucible of magnesium oxide
b) shaker of
salt
f) air bag full of nitrogen gas
c) bottle of
water
g) Neon sign
d) He filled
balloon
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?
More Examples:
Calculate how many grams are in 0.700 moles of H_{2}O_{2}
Example:
Convert 2.50 moles of KClO_{3} to grams
2. Given Grams, Convert to Moles
Three steps:
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
grams.
How many moles is this?
More Example:
Convert 25.0 grams of KMnO_{4} to moles
Example:
Calculate how many moles are in 17.0 grams of H_{2}O_{2}
3. How many Representative Particles (Atoms or Molecules or Formula Units) ?
Three steps:
1)Determine
how many moles are given in the problem.
2)Use
the relationship: 6.02 x 10^{23} representative
particles = 1 mole
3)Use
dimensional analysis to setup the problem.
Example: Propane (C3H8)
is a gas used for cooking and heating.
How many
molecules are in
2.12 mol of propane?
More examples:
How many moles is 2.80 x 10 ^{24} atoms
of silicon?
How many moles is 2.17 x 10 ^{23} molecules
of bromine?
4)
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
Example: H_{2}S
. 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 ____ :
_____atom ratio
50,000 atoms H : ______________ atoms S
or ______________ atoms H : 6.02 x 10^{23} atoms S
. using the mole: the ____________ equals the
___________ equals
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 C_{4}H_{10} not C_{2}H_{5}
. to find the true formula: 1) find the empirical formula 2) need the mass of the actual formula (Formula Weight)
