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# Chemistry I Chapter 3 CH 1213

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This 13 page Class Notes was uploaded by Katerina Kushla on Thursday September 8, 2016. The Class Notes belongs to CH 1213 at Mississippi State University taught by Dr. Eric Van Dornshuld in Fall 2016. Since its upload, it has received 16 views. For similar materials see Chemistry 1 in Chemistry at Mississippi State University.

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Date Created: 09/08/16

Chapter 3: Compositions of Substances and Solutions Formula Mass (formula weight) – for ionic compounds - The sum of the average masses for all atoms represented in a chemical formula - Ex. – CHCl3 C = 12.011 H= 1.008 Cl = 35.45 x 3 = 106.35 12.011 + 1.008 + 106.35 = 119.369 amu Molecular Mass (molecular weight) – for covalent compounds - The sum of the average masses for all atoms represented in a chemical formula - Ex. – NaCl Na = 22.99 Cl = 35.45 22.99 + 35.45 = 58.44 amu 3.1 – Formula Mass and the Mole Concept Mole – defined as the amount of substance containing the same number of discrete entities as the number of atoms in a sample of pure Carbon 12 weighing exactly 12 grams. A mole is just a number. A big number. Just like a pair is 2, or a dozen is 12, a mole stands for a numerical value. That value is 6.022 x 10 .23 The mole is often referred to as “Avogadro’s number” written as N A 23 N A 6. 022 x 10 = 1 mole Molar Mass – the mass in grams of 1 mole of the given substance (grams per mole) Percent Composition – the percentage (by mass) of each element in a compound Determining Empirical formula from Mass: Summary of Steps: 1. Convert mass to moles – subscripts for elements 2. Divide each subscript by the smallest number 3. Multiply al subscripts by an integer, if necessary, to get whole numbers Summary of Steps: 1. Convert mass to moles – subscripts for elements 2. Divide each subscript by the smallest number 3. Multiply al subscripts by an integer, if necessary, to get whole numbers Determine Empirical Formula from Percent Composition: Summary of Steps 1. Always assume 100 g sample (to easily convert for percentages to grams) 2. Convert mass to moles 3. Divide through by smallest subscript 4. Multiply all subscripts by an integer, if necessary, to get whole numbers Determine Molecular Formulas from Empirical Formulas: Summary of Steps 1. Determine empirical formula from mass or percent composition 2. Determine, if necessary, the molar mass of the sample 3. Divide molar mass of sample by empirical formula mass 4. Multiply all subscripts in empirical formula by the number determined in Step 3 3.3 - Molarity Solution – homogeneous mixtures made up of solute(s) and a solvent Concentration – the relative amount of a given solution component; generally given as molarity Molarity (M) – a useful unit for concentration; defined as the number of moles of solute in exactly 1 L of solution Mol solute M = L solution Solvent – the component of a solution that has the largest concentration relative to the other components Solute – a component of a solution that is not the solvent Dilute – qualitative description of solute concentration; relatively low concentration Concentrated – qualitative description of solute concentration; relatively high concentration Find M from moles of solute Ex. – A 10.0 mL solution contains 0.001 mol of sodium chloride. What is the molar concentration of sodium chloride? Summary of Steps: 1. Find moles of solute (mass to moles) 2. Find L of solution 3. Implement molarity equation Find M from mass of solute A 650 mL solution contains 5.00 g of benzene (C H 6.6What is the molar concentration of benzene? Summary of Steps: 1. Find moles of solute (mass to moles) 2. Find L of solution 3. Implement molarity equation Find moles of solute and mass of solute from M How many grams of table sugar (molar mass = 342.3 g/mol) is contained in a can of Pepsi (335 mL)? The concentration of the sugar is about 0.338 mol/L. Summary of steps: 1. Find mole of solute (rearrange molarity equation). Be sure volume is in L. 2. Convert moles to mass (multiply by molar mass) Find volume of solution from mass of solute and M The typical concentration of vinegar is 0.839 M. What volume of vinegar contains 75.6 g of acetic acid? Summary of steps: 1. Convert mass to moles 2. Solve for L of solution Dilution of Solutions Dilution – the process whereby the concentration of a solution is decreased by the addition of solvent * The original, concentration solution is the stock solution C V = C V 1 1 2 2 Find concentration of dilute solution If 0.0500 L of a 10.00 M solution of sodium chloride is diluted to a volume of 1.20 x 10 mL by the addition of water, what is the molarity of the diluted solution? Find volume of diluted solution What volume (in L) of 0.05 M H O can b2 2ade from 20.0 ml of 0.82 M H O ? 2 2 Find volume of a concentration solution needed for dilution What volume (in L) of 8.00 M HCl is required to prepare 10.0 L of 0.200 M HCl? Summary of Steps: 1. Identify what is given and what you are solving for 2. Rearrange dilution equation to solve for unknown 3. Convert, if necessary, any givens to appropriate units 4. Solve for the unknown

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