Chemistry Chapter 3 Notes
Chemistry Chapter 3 Notes CH1213
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This 2 page Class Notes was uploaded by alb1081 on Friday September 9, 2016. The Class Notes belongs to CH1213 at Mississippi State University taught by Dr. Xiu Xu in Fall 2016. Since its upload, it has received 4 views. For similar materials see Chemistry 1 in Chemistry at Mississippi State University.
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Date Created: 09/09/16
I. Composition of Substances and Solutions A. Molecular Mass and Formula Mass 1. Molecular mass – the mass in amu of an individual molecule 2. Multiply atomic mass for each element in a molecule by the number of atoms and then total the masses 3. The result is an average molecular mass or molecular weight 4. Formula mass or formula weight to accurately express ionic compounds i. The process is the same ii. Ionic compounds have the same empirical formula and molecular formula B. The Mole and Molar Mass 1. A mole is the amount of substance that contains as many elementary entities as there are atoms in exactly 12 g of carbon-12 i. Avogadro’s number (N sub A) = 1 mole = 6.0221415 x 10^23 ii. Normally rounded to 6.022 x 10^23 = 1g/1amu iii. 1 amu x N sub A = 1 g 2. Moles are only used with elements and compounds 3. Molar Mass – mass in grams of one mole of the substance i. By definition, the mass of a mole of carbon-12 is 12 g ii. Usually express molar mass in units of grams per mole 1. g to mol = g x 1/molar mass (mol/g) 2. mol to g = mol x molar mass (g/mol) 4. Moles to molecules = mol x N sub A 5. Molecules to moles = x 1/N sub A C. Percent Composition of Compounds 1. Percent mass of element = (n x atomic mass of element)/(molecular formula of compound) x 100 2. Can use empirical or molecular formula 3. Can use empirical formula mass, the mass in amu of one empirical formula, in place of a molecular formula 4. You can get empirical formula from mass percentage 5. You cannot get molecular formula 6. Percent compositions to formulas i. Assume exactly 100 g so percentages convert directly to grams ii. Convert grams to moles for each element iii. Manipulate the resulting mol ratios to obtain whole numbers 1. If decimal is 0.5, multiply by 2 2. If decimal is 0.33 or 0.67, multiply by 3 3. If decimal is 0.25 or 0.75, multiply by 4 iv. To find molecular formulas: 1. Compute empirical formula 2. Find ration of molecular weight to empirical formula weight 3. Multiply each subscript by n D. Concentrations of Solutions 1. Molarity (M), or molecular concentration, is defined as the number of moles of solute per liter of solution i. M = moles solute/liters solute E. Dilution 1. Dilution is the process of preparing a less concentrated solution from a more concentrated one. i. Moles of solute before dilution = moles of solute after dilution ii. M1 x L1 = M2 x L2