Unit 2 Lesson 3 Molarity Video Disk Unit 6 Demo Magic Sand Savery’s Fire Engine Melting Mole Dollars

Concentrations of Solutions We must have some way of discussing how much solute is in the solvent. A dilute solution has a little solute. A concentrated solution has a lot of solute. These terms a general terms and do not tell us exactly how much solute is in a solution Dilute and concentrated are comparison terms, and thus a judgment call on the part of the describer.

Molarity The Molarity of a solution defines the Exact amount of solute in the solution in moles per Liter. Molarity = Capital M = Molarity = unit for concentration This formula is listed on the formula page of your reference packet!

Example What is the molarity of a solution formed by mixing 0.102 moles of H2SO4 with enough water to make 100.0 mL of solution?

M = mol / L M = 1.02 M H2SO4

Sample Problem Vinegar is a solution of acetic acid. What is the molarity of the solution produced when 2.085 moles of acetic acid (HC2H3O2) are dissolved in sufficient water to prepare 1.50 L of solution? 1.39 M

M1V1 = M2V2 Diluting a Solution If you want to dilute a solution with a known concentration use the formula: M1V1 = M2V2 M1 is molarity of original solution V1 is volume of original solution M2 is molarity of diluted solution V2 is volume of diluted solution Also in your ref. pack.

Example How do you make 500. mL of 3.00 M sulfuric acid solution using 18.0 M sulfuric acid? M1V1 = M2V2 V1 = (3.00 M)(.500 L) 18.0 M V1 = 0.0833 L = 83.3 mL Use 83.3 mL of 18.0 M H2SO4 and dilute to 500. mL with water to make a 3.00 M solution.

Example Dilute 25.0 mL of 12.0 M Hydrochloric acid to 500.0 mL. What is the new concentration of the diluted solution? M1V1 = M2V2 (12.0 M)(0.0250 L) = M2 0.5000 L M2 = 0.600 M

Example How much water needs to be added to 25.0 mL of a 0.750M solution of HCl to dilute it to 0.100M? M1V1 = M2V2 (0.750 M)(0.0250L) = V2 0.100 M V2 = 188 mL (doesn’t answer question) Need to add 188 mL – 25.0 mL = 163 mL

Connecting to colligative properties Calculate the molarity of a 1000. mL solution that has 0.50 mol of NaCl dissolved in it. Calculate the new molarity if 1000. mL of water are added to the solution. M1V1 = M2V2 (0.50 M)(1.000 L) = M2(2.000 L) M2 = 0.25 M Which solution will have the lowest freezing point? Which solution will have the lowest boiling point? Which solution will have the highest vapor pressure? M = mol L M = 0.50 mol 1.000L M = 0.50 mol L = 0.50 M 0.50 M 0.25 M 0.25 M