Moles - mleonessciencepage

Report
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

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