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Chapter 3 Mass Relationships in Chemical Reactions. Section 3.6 – 3.9. These Sections Will NOT be on EXAM 1. Concentrations of Reactants in Solution: Molarity. Molarity: The number of moles of a substance dissolved in each liter of solution. Solution: A homogeneous mixture.
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Chapter 3Mass Relationships in Chemical Reactions Section 3.6 – 3.9 These Sections Will NOT be on EXAM 1
Concentrations of Reactants in Solution: Molarity • Molarity: The number of moles of a substance dissolved in each liter of solution. • Solution: A homogeneous mixture. • Solute: The dissolved substance in a solution. • Solvent: The major component in a solution
molarity = moles of solute liters of solution Concentrations of Reactants in Solution: Molarity Molarity converts between mole of solute and liters of solution: 1.00 mol of sodium chloride placed in enough water to make 1.00 L of solution would have a concentration equal to: 1.00 mol mol = 1.00 or 1.00 M 1.00 L L
Concentrations of Reactants in Solution: Molarity What is the molarity of a solution made by dissolving 2.5 g of NaCl in enough water to make 125 ml of solution? How many grams of solute would you use to prepare 1.50 L of 0.250 M glucose, C6H12O6? Calculate the volume of a 0.80M potassium bromide solution containing 23.6 g of potassium bromide.
concentrated solution + solvent dilute solution Diluting Concentrated Solutions initial final MiVi = MfVf Or M1V1 = M2V2 Since the number of moles of solute remains constant, all that changes is the volume of solution by adding more solvent.
Diluting Concentrated Solutions 1. Sulfuric acid is normally purchased at a concentration of 18.0 M. How would you prepare 250.0 mL of 0.500 M aqueous H2SO4? 2. To what volume should you dilute 0.200 L of a 15.0 M NaOH solution to obtain a 3.00 M NaOH solution?
aA + bB cC + dD Solution Stoichiometry Volume of Solution of A Moles of A Moles of B Volume of Solution of B Molarity of A Mole Ratio Between A and B (Coefficients) Molar Mass of B
H2SO4(aq) + 2NaOH(aq) Na2SO4(aq) + 2H2O(l) Solution Stoichiometry What volume of 0.250 M H2SO4 is needed to react with 50.0 mL of 0.100 M NaOH? Volume of Solution of H2SO4 Moles of H2SO4 Moles of NaOH Volume of Solution of NaOH Molarity of H2SO4 Molarity of NaOH Mole Ratio Between H2SO4 and NaOH
Example • What is the minimum amount (L) of 6.0 M H2SO4 necessary to produce 25.0 g Assumed H2SO4 is limited 2 Al(s) + 3 H2SO4(aq) Al2(SO4)3(aq) + 3 H2(g)
HCl(aq) + NaOH(aq) NaCl(aq) + 2H2O(l) Titration Titration: A procedure for determining the concentration of a solution by allowing a carefully measured volume to react with a solution of another substance (the standard solution) whose concentration is known. Once the reaction is complete you can calculate the concentration of the unknown solution. How can you tell when the reaction is complete?
Titration standard solution (known concentration) buret Erlenmeyer flask unknown concentration solution An indicator is added which changes color once the reaction is complete
HCl(aq) + NaOH(aq) NaCl(aq) + 2H2O(l) Titration 48.6 mL of a 0.100 M NaOH solution is needed to react with 20.0 mL of an unknown HCl concentration. What is the concentration of the HCl solution? Concentration of HCl Volume of Solution of NaOH Moles of NaOH Moles of HCl Molarity of NaOH Mole Ratio Between NaOH and HCl Volume of HCl
Example • What volume (in mL) of a 0.150 M HNO3 solution is required to completely react with 35.7 mL of a 0.108 M Na2CO3 solution according to the following balanced chemical equation? Na2CO3(aq) + 2 HNO3(aq) -- > 2 NaNO3(aq) + CO2(g) + H2O(l)