Week 1 Lecture 3 Notes
Week 1 Lecture 3 Notes CHM 2045
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This 3 page Class Notes was uploaded by Daniel Donovan on Wednesday September 14, 2016. The Class Notes belongs to CHM 2045 at University of Florida taught by Dr. Martina Sumner in Fall 2016. Since its upload, it has received 36 views. For similar materials see Freshman Chemistry 1 in Chemistry at University of Florida.
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Date Created: 09/14/16
CHM2045 Lecture 3 Chapter 3 Section 3.1 The Mole Avogadro’s Number: o Avogadro’s number (N )A number of particles (atoms, ions, molecules, skittles, snowflakes, m&ms, marbles, etc.) in one mole is equal to the number of atoms in exactly 12 g of carbon-12. o 6.022*10 23anything/mole o Mole of marbles would be 70 miles deep above US Determining Molar Mass: NaCl o Mass (g) of NaCl = (mass of Na) + (mass of Cl) = 23 + 35.45 = 58.45 g NaCl Calcium nitrate o Find the chemical formula o Find Mass Mass (g) of CaNO =3(mass of Ca) + (mass of N) + (mass of O *3) = 40.078 + 14.0067 + (15.999 * 3) = 372.5 g CaNO 3 Converting between amount, mass, and number of chemical entities: o Ex. How many g is 2.3 moles of water? o 2.3 moles H 2 * (18 g H O2/ mole) = 41.4 g H O2 Steps to convert: G -> moles: 1. Cancel out grams by putting the molar mass of the compound to cancel out the grams and leave you with moles for your final answer. Moles -> G: 2. Do the opposite of g->moles except cancel out moles. Moles to moles: 3. Set up the molar ratio (the small number below the element) G -> g: 4. Cancel out the grams by finding the molar mass in one mole of the compound (ex H2O) 5. Once you have moles of the compound, set up the molar ratio in order to get the moles of the element or compound that you are trying to find. 6. Calculate the mass of 1 mole of the compound or element in order to get the final answer in grams. The Importance of mass percent o Determining mass percent from a chemical formula o What is the mass percent of each element in ammonium phosphate? Steps to Solve: 1. Find the chemical formula of the compound 2. Find the total mass of the compound 3. Once the total mass of the compound is found, find the mass of each of the components of the compound. 4. Divide the mass of each of the components by the total mass and multiply by 100. 5. Write down the final answer. Solution: Mass (g) of (NH4 3PO4= 149.09 g Mass percent of N = ((3*14.0067 g) / (149.09 g)) * 100 Follow the same process for each of the elements 3.2 Determining the formula of an unknown compound o Empirical formulas: are the simplest whole-number of ratio of atoms of each element present in a compound. Molecular formula is the real number of atoms. o Ex. CH C6H 6 The % composition of any element is equal to the mass of that element in exactly 100 g of compound. So 13.4% K = 13.4 g K / 100 g of compound Molecular Formula o Whole-number multiple of its empirical formula o (Molar mass of compound)/ (Molar mass of empirical formula) = whole number o Whole number multiple is equal to the number of empirical formula units in one molecule of a compound. o Molar mass of a compound must be determined in order to determine the molecular formula of a compound o Since the molecular formula is a multiple scaled by a factor “n”, the molecular and empirical molar masses must scale by the same ratio o (Molar formula mass (g/mol)) / (empirical formula mass (g/mol)) Combustion Analysis of Organic Compounds: o Chemical analysis: determine the nature and the number of chemicals species present. o Combustion analysis: determines chemical formula of a compound that contains C and H. Do a combustion reaction (burn chemical with molecular oxygen to give water and carbon dioxide). All the C ends up in CO2and the H in H 2. Determining the Formula of a Compound by Combustion: o Combustion involves the addition of oxygen to another element. o When hydrocarbon molecules burn completely, the products are always carbon dioxide gas and water. o Incomplete combustion produces CO and water
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