John E. McMurry Robert C. Fay C H E M I S T R Y Sixth Edition Chapter 3 Mass Relationships in Chemical Reactions 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. In practice, a solution of known molarity is prepared by weighing an appropriate amount of solute, placing it in a container called a volumetric flask, and adding enough solvent until an accurately calibrated final volume is reached. Solution: A homogeneous mixture. Solute: The dissolved substance in a solution. Solvent: The major component in a solution.

Concentrations of Reactants in Solution: Molarity

Molarity converts between mole of solute and liters of solution: molarity = moles of solute liters of solution L mol or 1.00 M 1.00 L 1.00 mol = mol of sodium chloride placed in enough water to make 1.00 L of solution would have a concentration equal to:

Example What is the molarity of a solution made by dissolving 2.5 g of NaCl in enough water to make 125 ml of solution?

Concentrations of Reactants in Solution: Molarity How many grams of solute would you use to prepare 1.50 L of M glucose, C 6 H 12 O 6 ? Calculate the volume of a 0.80M potassium bromide solution containing 23.6 g of potassium bromide.

Diluting Concentrated Solutions dilute solutionconcentrated solution + solvent M i V i = M f V f finalinitial Since the number of moles of solute remains constant, all that changes is the volume of solution by adding more solvent. Or M1V1 = M2V2

Diluting Concentrated Solutions 1.Sulfuric acid is normally purchased at a concentration of 18.0 M. How would you prepare mL of M aqueous H 2 SO 4 ? 2.You have 53.0 ml of a 1.5 M solution of NaCl, but 0.8 M solution is needed. How many ml of 0.8 M can you make?

Solution Stoichiometry aA + bB cC + dD Moles of A Volume of Solution of A Moles of B Volume of Solution of B Mole Ratio Between A and B (Coefficients) Molar Mass of B Molarity of A

Solution Stoichiometry H 2 SO 4 (aq) + 2NaOH(aq) Na 2 SO 4 (aq) + 2H 2 O(l) What volume of M H 2 SO 4 is needed to react with 50.0 mL of M NaOH? Moles of H 2 SO 4 Volume of Solution of H 2 SO 4 Moles of NaOH Volume of Solution of NaOH Mole Ratio Between H 2 SO 4 and NaOH Molarity of NaOH Molarity of H 2 SO 4

Example What is the minimum amount (L) of 6.0 M H 2 SO 4 necessary to produce 25.0 g H2 of 0.150M Co(NO 3 ) 2. Assumed H 2 SO 4 is limited 2 Al(s) + 3 H 2 SO 4 (aq)  Al2(SO 4 ) 3 (aq) + 3 H 2 (g)

Titration How can you tell when the reaction is complete? HCl(aq) + NaOH(aq) NaCl(aq) + 2H 2 O(l) 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.

Titration unknown concentration solution Erlenmeyer flask buret standard solution (known concentration) An indicator is added which changes color once the reaction is complete

Titration HCl(aq) + NaOH(aq) NaCl(aq) + 2H 2 O(l) 48.6 mL of a M NaOH solution is needed to react with 20.0 mL of an unknown HCl concentration. What is the concentration of the HCl solution? Moles of NaOH Volume of Solution of NaOH Moles of HCl Volume of Solution of HCl Mole Ratio Between NaOH and HCl Molarity of HClMolarity of NaOH

Example Titration reveals that 11.6 mL of 3.0 M sulfuric acid are required to neutralize in NaOH solution. Determine the volume of 2.8 MNaOH solution that is needed for this titration?