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What is a Mole Chemists use the mole to count microscopic particles. How many socks come in a pair? 2 How many eggs are in a dozen? 12 How many eggs come in a gross? 144 How many pencils come in a ream? 500 So how many atoms come in a mole? 602,213,670,000,000,000,000,000. Seriously This number was created by an Italian physicist and lawyer named Amedeo Avogadro. Its called Avogadro’s Number. Is there an easier way to write it? 6.02 x 1023 items = 1 mole Converting between moles and number of particles Think about eggs 1 dozen eggs = 12 eggs Conversion factor: 12 eggs/1 dozen eggs OR 1 dozen eggs/12 eggs So if you have 3.5 dozen eggs how many eggs do you have? 3.5 dozen x (12 eggs)/1 dozen = 42 eggs If you have 3.5 moles of sugar how many particles of sugar do you have? 1 mole of sugar = 6.02 x 1023 particles of sugar. Set up the problem: 3.5 moles x (6.02 x 1023 particles/1 mole) Solve: 2.107 x 1024 Zinc (Zn) is used to form a corrosion-inhibiting surface on galvanized steel. Determine the number of Zn atoms in 2.50 moles of Zn. 1.51 x 1024 atoms Calculate the number of molecules in 11.5 mol of water. 6.92 x 1024 molecules Silver nitrate Ag(NO3)2 is used to make several different compounds used in photographic films. How many molecules of silver nitrate are there in 3.25 moles of Ag(NO3)2? 1.96 x 1024 How many atoms of oxygen are there in 5.0 mol of oxygen gas? 6.02 x 1024 atoms Converting from number of particles to moles Calculate the number of moles of Zinc that contains 4.50 x 1024 atoms. 0.914 moles How many moles can be made up from 5.57 x 1024 atoms of Al? 9.55 moles How many moles can be made up from 2.5 x 1025 atoms of Fe? 41.5 moles What would have more mass a dozen eggs or a dozen elephants? Why would a dozen elephants have more mass? Just like elephants and eggs certain atoms are bigger than others. For example Neon is much bigger than Helium. Which would have more mass 1 mole of Neon or 1 mole of Helium? Molar Mass The molar mass of an element is the mass in grams of one mole of that element. Why is this important? Molar mass can be used to calculate the number of atoms with out using a microscope. Using molar mass If one dozen jelly beans has a mass of 35 g how much mass does 5 dozen jelly beans have? 175 g To convert from Moles to mass you multiply by the molar mass. What is the mass of 3.oo moles of copper? 191 g cu. To convert from mass to moles you divide by the molar mass. Example Problems Chromium (Cr), a transition element, is a component of chrome plating. Chrome plating is used on metals and steel alloys to control corrosion. Calculate the mass in grams of 0.045 moles of Cr. 2.34 g Cr Calcium (Ca), the fifth most abundant element on earth, is always found combined with other atoms because of its high reactivity. How many moles of calcium are in 525 g Ca? 13.1 moles Ca Converting between mass and atoms The next step is converting a given mass of an element into a number of atoms. If we have 550 g of jelly beans and there are 35 g of jelly beans in a dozen how many dozen jelly beans do we have? 16 dozen How many jelly beans are there in 16 dozen? 192 Mass-to-Atom Conversion Gold (Au) is one of a group of metals called the coinage metals. How many atoms of gold are there in a U.S. gold eagle coin with a mass of 31.1 g? 9.51 x 1022 Atom-to-Mass Conversion Helium (He) is an unreactive noble gas found underground. A party balloon contains 5.5 x 1022 atoms of helium gas. What is the mass, in grams, of the helium? 0.366 g Homework Textbook (sorry) P. 328 # 15(a&b), 16(a&b) P. 329 # 17(a&b), 18(a&b) P. 331 # 19(a&b), 20(a&b) Chemical Formulas and the Mole In the compound CCl2F2 how many atoms do we have? C: 1 Cl: 2 F: 2 So if we have one mole of CCl2F2 we have one mole of carbon, two moles of Chlorine and one mole of Fluorine. Molar Mass of a Compound Determine the molar mass of each of the following compounds: NaOH CaCl2 KC2H3O2 C2H5OH HCN CCl4 (NH4)3PO4 Converting moles to mass The characteristic odor of garlic is due to allyl sulfide (C3H5)2S. What is the mass of 2.5 moles of allyl sulfide? What is the mass of 3.25 mol of H2SO4? Converting Mass to Moles Calculate the number of moles in 325 g of Calcium hydroxide Ca(OH)2? Calculate the number of moles in 22.6 g of AgNO3. Mass to Number of Particles Aluminum chloride (AlCl3) is used in refining petroleum and manufacturing rubber. How many Aluminum Chloride molecules are present in 35.6 g of AlCl3 How many Al atoms are there? How many Cl atoms are there? Example Aluminum oxide (Al2O3) when dissolved in water breaks apart into ions (Al3+ and O2-) how many moles of Al3+ will be produced when 1.5 moles of Al2O3 are dissolved in water? Examples What is the molar mass of ethanol C2H5OH? 1. How many ethanol molecules are present in 45.6 g? How many carbon atoms are there in 45.6 g of ethanol? How many hydrogen atoms are there in 45.6 g of ethanol? How many oxygen atoms are there in 45.6 g of ethanol? A sample of sodium sulfite Na2SO3 has a mass of 2.25 g 2. How many molecules of sodium sulfite are there? How many atoms of sodium are there? How many atoms of Sulfur are there? How many atoms of oxygen are there? Percent Composition A compound is made up of one or more atoms bonded together. Each of the atoms contributes mass to the compound. Example: The molar mass of NaOH is Na – 22.98 g/mol O – 16 g/mol H – 1 g/mol Total: 39.98 g/mol Calculating Percent Composition Percent composition is calculated by dividing the mass of an individual element by the mass of the whole compound and then multiplying by 100. NaOH: Percent Composition of Na: (22.98/39.98) x 100 = 57.5% Percent Composition of O: (16/39.98) x 100 = 40% Percent Composition of H: (1/39.98) x 100 = 2.5% Compounds with multiple atoms of the same element NaHCO3 Molar Mass: 84.01 g/mol Percent Composition of Na: (22.98/84.01) x 100 = 27.37% Percent Composition of H: (1/84.o1) x 100 = 1.2% Percent Composition of C: (12.01/84.01) x 100 = 14.3% Percent Composition of O: (48/84.01) x 100 = 57.14% Empirical Formula When we know a compounds percent composition we can determine it’s formula. The empirical formula of a compound is the formula with the smallest whole-number ratio of elements. Find the empirical formula for a compound that is 40.05% S and 59.95% O. If we assume that we have 100 g of this compound: How many grams of Sulfur do we have? 40.05 g How many grams of Oxygen do we have? 59.95 g Convert from grams to moles: 40.05 g S x 1 mol S/32.07 g S = 1.249 mol 59.95 g O x 1 mol O/16.00 g O = 3.747 mol S1.249O3.747 SO3 Sometimes the empirical formula is not the actual formula for the compound. Find the empirical formula for hydrogen peroxide which has a molar mass of 34 g/mol and is 5.9% Hydrogen and 94.1% Oxygen Molecular Formula A compounds molecular formula is its actual formula (not always the same as empirical formula) To determine the true molecular formula for a compound its molar mass must be known (either looked up or found experimentally). Once we know the molar mass and the empirical formula we can find the true formula of the compound. Example: Acetylene is a highly flammable compound used in blow torches. Acetylene has a molar mass of 26.04 g/mol. It is 92.2% Carbon and 7.8% Hydrogen. What is the chemical formula of Acetylene? Step 1: Find empirical formula: CH Step 2: Calculate molar mass of empirical formula. (If the molar mass is the same as the actual molar mass then the empirical formula is the true formula.) 13.02 g/mol Step 3: Divide real molar mass by the molar mass of the empirical formula. 26.04/13.02 = 2.000 Step 4: Multiply all atoms in the empirical formula by the answer to the true formula. C2H2