2 ObjectivesDescribe the concentration of solutions using different units.Determine the concentrations of solutions.Calculate the molarity of a solution.
3 Solution Concentration The concentration of a solution is a measure of how much solute is dissolved in a specific amount of solvent or solution.Qualitative: concentrated or dilute.dilute concentrated
4 Expressing Concentration Qualitative Descriptionsconcentrated: a large amount of solutedilute: a small amount of soluteQuantitative DescriptionsPercent by either mass or volumeMolarityMolalityMole Fraction
5 Percent by Mass % by mass = mass of solute x 100 mass of solution Note: mass of solution = mass solute + mass solventIn order to maintain a sodium chloride (NaCl) concentration similar to ocean water, an aquarium must contain 3.6 g NaCl per 100 g of water. What is the % by mass of NaCl in the solution?The % by mass of a NaOCl solution is 3.62%. If you have 1500 g of solution, how much NaOCl do you have?3.5 %
6 % by volume = volume of solute x 100 Percent by Volume% by volume = volume of solute x 100volume of solutionNote: vol. of solution = vol. solute + vol. solventWhat is the percent by volume of ethanol in a solution that contains 35 mL of ethanol dissolved in 115 mL of water?If you have 15 mL of 70% isopropyl alcohol solution, how many mLs of alcohol are in the solution?2.3 %
7 MolarityMolarity (M) or molar concentration is the number of moles of solute dissolved per liter of solution.M is read as molar. For example, 0.5 M HCl is a 0.5 molar solution of HCl. It contains 0.5 moles of HCl in every liter of solution.
8 Molarity To calculate molarity: mind that there are 1000 mL in 1 L & convert to L
9 Molarity Practice Problems A mL intravenous (IV) solution contains 5.10 g of glucose (C6H12O6). What is the molarity of this solution? The molar mass of glucose is 180 g/mol.Calculate the molarity of L of a solution containing 1.55 g of dissolved KBr.What is the molarity of an aqueous solution containing 40.0 g of glucose in 1.5 L of solution?.28M
11 Preparing Molar Solutions So, for 1 L of a 1M solution, you would need 1 mole of the salt, or g NaCl.What if you needed 1 L of a 0.3 M solution?M = moles solute or M = x molesliters solution Lx = 0.3 mol or 17.6 gWhat if you only needed 150 mL of the 0.3 M solution?M = moles solute or M = x molesliters solution Lx = mol or 2.63 g
12 Preparing Molar Solutions 1.0 L of a 0.10 M solution of CaCl2 is needed. How many grams of CaCl2 must be added to water to prepare this solution?How many grams of NaOH are needed to make 250 mL of a 3.0 M NaOH solution?500 mL of a 2 M NaOH solution contains how many grams of NaOH?9.0 ^ -4 g CaCl2
13 Diluting SolutionsConcentrated solutions called stock solutions are sold for laboratory use.Stock solutions are then diluted to prepare less concentrated solutions.When you add solvent to small amounts of concentrated solutions, you increase the number of solvent particles and, thus, decrease the solution’s concentration.
14 Mstock x volume stock = Mdil x volume of dilute Diluting SolutionsRecall: M = moles solute/liters solutionmoles solute = M x liters solutionThe # of moles of solute does not change during dilution - the # of solvent particles changes.That means,moles of solute in stock = moles of solute in diluted solutionMstock x volume stock = Mdil x volume of diluteorM1V1 = M2V2
16 Diluting Sol’ns Practice Problems What volume, in milliliters of 2.00 M of calcium chloride (CaCl2) stock solution would you use to make a 0.50 L of M calcium chloride solution?If you dilute 20.0 mL of a 3.5 M solution to make 100 mL of solution, what is the molarity of the dilute solution?What volume of a 3.00 M KI stock solution would you use to make L of a 1.25 M KI solution?75 mL
17 MolalityIf there is a temperature change, the volume of a solution will change.If volume changes, the molarity will change.Therefore, there is a need for an alternative way to express concentration.Since masses do NOT change with temperature, concentration can be expressed in terms of moles of solute in a mass of solvent.
18 MolalityThe molality of a solution, denoted m, is defined as the number of moles of solute dissolved in one kilogram of solvent:“1 m” is read as a 1 molal solution.Recall: 1000 g = 1 kg
19 MolalityIn the lab, a student adds 4.5 g of sodium chloride (NaCl) to 100 g of water. Calculate the molality of the solution.A solution has naphthalene (C10H8) dissolved in 500 g of toluene. The solution has a molality of m. How many grams of naphthalene are in the solution?What is the molality of a solution containing 10.0 g of Na2SO4 dissolved in 1000 g of water?0.77 mol/kg
20 Mole FractionMole fraction is the ratio of the number of moles of solute (or solvent) in a solution to the total number of moles of solute and solvent.If X represents mole fraction and A represents the solute & B represents the solvent,XA = nA XB = nBnA+ nB nA+ nBNote: XA + XB = 1(The sum of all the fractional componentsequals “the whole.”)
21 Mole FractionWhat is the mole fraction of HCl in a 100 g of an aqueous solution if it contains 37.5 g HCl? What is the mole fraction of water?What is the mole fraction of NaOH in an aqueous solution that contains 22.8 % NaOH by mass?Calculate the mole fraction of NaCl in a solution in which 15.7 g NaCl is dissolved in g H2O.0.206