Moles - mleonessciencepage
Download
Report
Transcript Moles - mleonessciencepage
Measurement of Matter: The Mole
How do you measure matter?
What are the three different ways we
Can measure things?
count
mass
volume
CONVERSIONS
A pair Equals
2
A dozen equals
12
1 minute equals how
60
many seconds?
1 hour equals how many
minutes
60
CHEMICAL QUANTITIES
http://www.youtube.com/watch?v=1R7NiIum2TI
THE MOLE
How do we count matter?
Composed of atoms, molecules and ions
The mole is an equality that describes the number of
particles in a substance
6.02 x 10 23 particles,atoms ect.. = 1 mole ( avogadro’s
number)
Practice Problem
How many moles of magnesium is 1.25 x 1023 atoms of
magnesium
1. Start with what you know
1.25 x 10 23 atoms of Mg
1 mole of Mg
6.02 X 10 23 atoms of mg
= 0.208 mol Mg
REVIEW
1. How many atoms are in 1.14 mol of SO3
2. How many moles are in 4.65 x10 24 molecules of NO2
How many atoms are in 1.50 mols of Na
determine the number of moles in 4.96 x 10 24
molecules glucose
Mass of a Mole in an element
The atomic mass of an element expressed in grams is
the mass of a mole of the element = molar mass
Ex. Carbons molar mass = 12.0g
Hydrogens molar mass = 1.0 g
The molar masses of any two elements contains the
same number of atoms
12.0 g of carbon = 1 mol = 6.02 x 10 23 particles
1.0 g of hydrogen = 1 mol = 6.023 x 10 23 particles
Mass of a mole of a compound
Must know the formula of the compound first
Ex. SO3
1 sulfur ( 1 x 32.1) 32.1 amu
3 oxygen ( 3 x 16.0) = 48.0 amu
molar mass = 48.0 + 32.1 = 80.1 amu
1 mol has a mass of 80.1 amu
Review
What is the molar mass of PCl3
How many atoms are in 1.50 mols of Na
MASS/MOLE RELATIONSHIPS
Remember: to calculate molar mass you must know
the number of grams of each element in one mole of
the compound and add the masses of all the elements
of the compound
You can use molar mass of an element or compound to
convert between the mass of a substance and the
moles of a substance
calculations
Calculate the mass of 3.00 mol of NaCl
Molar Mass of NaCl
Na = 23.9
Cl = 35.4
Total = 53.9 g
3.00 mol
54.9 g NaCl
1 mol NaCl
Converting mass to moles
How many moles of Iron (III) oxide are contained in
92.2 g of Fe2O3
92.2 g of Fe2O3 X 1 mol of Fe2O3
160 g Fe2O3
= .58 mol Fe2O3
GRAMS TO MOLECULES
How many grams are in 4.65 x10 24 molecules of NO2
Review Quiz
How many grams are in 4.65 x10 24 molecules of NO2
What is the molar mass of PCl3
What is the mass of 2.25 mol of NaCl
QUIZ
How many grams does
4.3 x 1021 molecules of MgCl2
have
PERCENT COMPOSITION
Percent Composition – the relative amounts of the
elements in a compound
Consists of a percent value for each different element
in a compound
CALCULATIONS
The percent by mass of an element in a compound is
the number of grams of the element divided by the
mass in grams of the compound, multiplied by 100%
% mass of element = mass of element
mass of compound
x 100
Practice
Propane (C3H8), the fuel commonly used in gas grills,
is one of the compounds obtained from petroleum.
Calculate the percent composition of propane
%C = 36.0g (3 X 12) x 100
= 81.8%
44.0g
%H = 8.0g
44.0g
x 100
= 18%
REVIEW QUIZ
Propane (C3H8), the fuel commonly used in gas grills,
is one of the compounds obtained from petroleum.
Calculate the percent composition of propane
Calculate the number of moles in 0.50 g of sodium
bromide (NaBr)
Review Quiz; % composition
What is the percent composition of baking soda
NaHCO3
Empirical/Molecular Formulas
The lowest whole number ratio of the atoms of the
elements in a compound
Molecular formula H2O2
Empirical formula HO
Determining empirical formulas
A compound is analyzed and found to contain 70.9%
potassium and 29.1%sulfer. What is the empirical formula of
the compound?
Percent you can assume 100
HINT:
% TO MASS
MASS TO MOLE
DIVIDE BY SMALLEST
MULTIPLY TILL WHOLE
70.9 g x 1 mol K = 1.8molK
39 g K
29.1 g x 1 mol S = .91 mol S
32 g S
Divide each molar quantity by the smaller number of
moles
1.85/.91 = 2 K
1. = .91/.91 = 1 S
K2S
MOLECULAR FORMULAS
Molecular formulas can be determine by empirical
formulas.
First calculate the empirical formula mass
Divide molecular mass by formula mass
Multiply each subscript in your formula by the factor
Practice problem
A compound with an empirical formula of CH2O has a
molecular mass of 90 amu. What is it’s molecular
formula
Determine empirical formula mass
C = 12 x1
H=1x2
O = 16 x 1
30
Divide the molecular mass by the empirical formula
mass to determine the multiple
90/30 = 3
Multiply the empirical formula by the multiple to find
the molecular formula
[CH2O] X 3 = C3H6O3
REVIEW QUIZ
A compound has 67.6% Hg, 10.8% S, and 21.6% O.
Determine the empirical formula
Find the molecular formula of ethylene glycol
(antifreeze). The molar mass is 62g/mol and the
empirical formula is CH3O