Chapter 03 - Stoichiometry and Chemical Equations Handout II

# Chapter 03 - Stoichiometry and Chemical Equations Handout...

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3-1 Stoichiometry of Formulas and Stoichiometry of Formulas and Equations III Equations III Chapter 3 Chapter 3

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3-2 Solution Stoichiometry • Many chemical reactions take place “in solution”  (in a solvent like water) • Often easier to store and mix than solids or gases • Amount of substance in a solution can be  measured very precisely • Environmental and biochemical reactions take  almost always place in an aqueous solution • Working with solutions, you need to know the  concentration , that is: the  molar amount of a  substance in that solvent
3-3 Solution Stoichiometry • Concentration – the amount of a solute (“ the dissolved  substance ”) dissolved in a given amount of  solvent – concentration expressed as “molarity” molarity  ( M ) = moles of solute/liters of solution •  = mol solute/L =  mol/L – intensive property • concentration does not change whether you take 50  mL or 500 L of that solution (see below)

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3-4 Solution Stoichiometry Calculate concentration Calculate the molarity of a 150.0 mL solution contain 10.0 g NaOH Answer - 10.0 g NaOH = 10.0 g / 40.0 (g/mol) = 0.25 mol - 0.25 mol in 150 mL = (150 mL/0.25 mol ) x (L/1000 mL ) = 1.67 mol/L
3-5 Solution Stoichiometry Calculate concentration How many grams of NaCl is required to make 200.0 mL of a 0.125 M solution? Answer - 0.125 M NaCl = 0.125 mol/L x 58.45 g/mol = 7.31 g/L - 200.0 mL = 200.0 mL x (1 L/1000 mL) = 0.2000 L - If there is 7.31 g NaCl in 1.0 L, there is 7.31 g/L x 0.2000 L = 1.46 g NaCl in 200.0 mL

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3-6 Laboratory Preparation of Molar Solutions - Weigh the solute needed - Transfer to volumetric flask filled half with solvent - Swirl or stir to dissolve solute - Add solvent until solution reaches its final volume (line on flask) Remember: the volume in molarity = volume of solution = volume of solvent + volume of solute
3-7 Diluting a Concentrated Solution

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Chapter 03 - Stoichiometry and Chemical Equations Handout...

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