measurement of matter: the mole
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Measurement of Matter: The Mole
How do you measure matter?
What are the three different ways weCan measure things?
countmassvolume
CONVERSIONSA pair Equals
A dozen equals1 minute equals how
many seconds?1 hour equals how
many minutes
21260
60
CHEMICAL QUANTITIES
http://www.youtube.com/watch?v=1R7NiIum2TI
THE MOLEHow do we count matter?
Composed of atoms, molecules and ionsThe 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 ProblemHow 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 Mg6.02 X 10 23 atoms of mg
= 0.208 mol Mg
REVIEW1. 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 elementThe 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 compoundMust know the formula of the compound firstEx. SO3
1 sulfur ( 1 x 32.1) 32.1 amu3 oxygen ( 3 x 16.0) = 48.0 amu
molar mass = 48.0 + 32.1 = 80.1 amu1 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 RELATIONSHIPSRemember: 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
calculationsCalculate the mass of 3.00 mol of NaClMolar Mass of NaClNa = 23.9Cl = 35.4Total = 53.9 g
3.00 mol 54.9 g NaCl
1 mol NaCl
Converting mass to molesHow 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 MOLECULESHow many grams are in 4.65 x10 24 molecules
of NO2
Review QuizHow 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 COMPOSITIONPercent Composition – the relative amounts
of the elements in a compound
Consists of a percent value for each different element in a compound
CALCULATIONSThe 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 x 100
mass of compound
PracticePropane (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 x 100 = 18% 44.0g
REVIEW QUIZPropane (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; % compositionWhat is the percent composition of baking
soda NaHCO3
Empirical/Molecular FormulasThe lowest whole number ratio of the atoms
of the elements in a compound
Molecular formula H2O2Empirical formula HO
Determining empirical formulasA 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
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
HINT:% TO MASSMASS TO MOLEDIVIDE BY SMALLESTMULTIPLY TILL WHOLE
Divide each molar quantity by the smaller number of moles 1.85/.91 = 2 K 1. = .91/.91 = 1 S
K2S
MOLECULAR FORMULASMolecular formulas can be determine by
empirical formulas.
First calculate the empirical formula massDivide molecular mass by formula massMultiply each subscript in your formula by
the factor
Practice problemA compound with an empirical formula of
CH2O has a molecular mass of 90 amu. What is it’s molecular formula
Determine empirical formula massC = 12 x1 H = 1 x 2O = 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 QUIZA 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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