# 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 we Can measure things? count mass volume

CONVERSIONS A pair Equals A dozen equals
1 minute equals how many seconds? 1 hour equals how many minutes 2 12 60

CHEMICAL QUANTITIES

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 particles,atoms ect.. = 1 mole ( avogadro’s number)

Practice Problem How many moles of magnesium is 1.25 x atoms of magnesium 1. Start with what you know 1.25 x atoms of Mg mole of Mg 6.02 X atoms of mg = 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 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 particles 1.0 g of hydrogen = 1 mol = x 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 = = 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
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 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 x 100 mass of compound

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 = 81.8% 44.0g %H = 8.0g x = 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 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 MASS MASS TO MOLE DIVIDE BY SMALLEST MULTIPLY TILL WHOLE

Divide each molar quantity by the smaller number of moles 1. 85/
Divide each molar quantity by the smaller number of moles /.91 = 2 K = .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 = 1 x 2 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