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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 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