1 SOLUTIONS A N I NTRODUCTION

2 Objectives 1. What are different ways of expressing the concentration of a solution? When is each used?

3 Solutions Solutions are homogeneous mixtures of two or more substances –Homogeneous: thoroughly mixed, even composition throughout Solute: substance being dissolved Solvent: substance doing the dissolving

4 Quantities of Solutes in Solution A dilute solution is one that contains relatively little solute in a large quantity of solvent. A concentrated solution contains a relatively large amount of solute in a given quantity of solvent A saturated solution contains the maximum amount of solute that can be dissolved in a particular quantity of solvent at equilibrium at a given temperature.

5 Solution Concentrations Need something more specific than concentrated and dilute –Molarity –Percent concentration –Mass/Volume Percent

6 Molarity Molarity is an expression of the concentration of a solution in moles of solute per liter of solution. A solute is a solution component that is dissolved in a solvent. The solvent is the solution component) in which one or more solutes are dissolved to form the solution Remember

7 Molarity Example Calculate the molarity of a solution made by dissolving moles of sodium sulfate (Na 2 SO 4 ) in enough water to form L of solution Read as ” molar sodium sulfate”

8 Molarity Example (2) Calculate the molarity of a solution made by dissolving 6.00 moles of Hydrogen Chloride (HCl) in enough water to form 2.50 L of solution

9 Molarity Examples Molarity of mol of Li 2 CO 3 in 10.0 mL of solution First convert to liters of solution

10 Molarity Examples 11. Calculate the molarity of each of the following solutions. a g of H 2 SO 4 in mL of solution First we need to know how many moles of H2SO4 we have Find Molar Mass of H2SO4 H 2 x g/mol= g/mol S 1 x g/mol = g/mol O4 x g/mol = g/mol Molar mass of H 2 SO 4 = g/mol

11 Molarity Examples b. 439 g of C 6 H 12 O 6 in 1.25 L of solution First we need to know how many moles of C 6 H 12 O 6 we have Find Molar Mass of C 6 H 12 O 6 C 6 x g/mol= g/mol H 12 x g/mol= g/mol O 6 x g/mol = g/mol Molar mass of C 6 H 12 O 6 = g/mol Find moles of C 6 H 12 O 6

12 Molarity Example (continued)

13 Molarity Examples How many grams of solute are needed to prepare each of the following solutions? a L of 1.00 M NaOH First we need to know the mass of one mole of NaOH Find Molar Mass of NaOH Na 1 x g/mol= g/mol H 1 x g/mol= g/mol O 1 x g/mol = g/mol Molar mass of NaOH = g/mol Board

14 Molarity Examples What volume of 6.00 M NaOH is required to contain 1.25 mol of NaOH?

15 Percent Concentrations Sometimes it is more convenient to express concentrations by percentages Percent by Volume Percent by mass

16 Percent Composition Examples What is the percent by volume of a solution made by dissolving 235 mL of ethanol in enough water to make exactly 500 mL of solution?

17 Volume Percentage Example Describe how to make 775 mL of a 40.0% by volume solution of acetic acid. Solve for Volume of solute Volume of solute = (% by volume) x (Volume of solution) 100% Volume of solute = (40.0% soln) x (775 mL soln) 100% Volume of solute = 310 mL of acetic actic Take 310 mL of acetic acid and add enough water to make 775 mL of solution

18 Volumetric Glassware Glassware designed for precisely making specific concentrations of solutions

19 Mass Percentage Example What is the percent by mass of a solution of 25.0 g of NaCl dissolved in 475 g (475 mL) of water?. First find total mass of solution mass of solution = 25.0 g of NaCl g of water = 500. g = 5.00 % NaCl solution

20 Mass Percentage Example Describe how to prepare 275 g of an aqueous solution that is 5.50% glucose by mass. Solve for mass of solute Mass of solute = (% by mass) x (Mass of solution) 100% Mass of solute = (5.50%(mass) soln of glucose) x (275 g of soln) 100% Mass of solute = 15.1 g of glucose Mass of solvent needed = Mass of solution – Mass of solute = 275 g – 15.1 g = 260 g of water Take 15.1 g of glucose and dissolve in 260 g of water

21 Mass/Volume Percent Mass/volume percent is an expression of concentration in which the mass of the solute is divided by the volume of the solution and that quotient multiplied by 100%. –U–Used in medicine In medical applications mg/dL = milligrams/deciliter is commonly used

22 Mass/Volume Percent For dilute aqueous solutions –Mass/Volume percent is close to Mass/Mass percent –This is because the density of a dilute aqueous solution is approximately 1 g/mL

23 Extremely Dilute solutions For extremely dilute solutions Concentrations expressed as –Parts per million (ppm) –Parts per Billion (ppm) –Parts per trillion (ppt) –1 ppm is 1 mg/L

24 Saturation Solubilities Curve gives maximum amount of solute dissolved at given temperature Most solubilities of ionic solids increase with Temperature