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1 SOLUTIONS A N I NTRODUCTION

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

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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

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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.

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

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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

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7 Molarity Example Calculate the molarity of a solution made by dissolving 0.165 moles of sodium sulfate (Na 2 SO 4 ) in enough water to form 0.500 L of solution Read as ” 0.330 molar sodium sulfate”

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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

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9 Molarity Examples Molarity of 0.00700 mol of Li 2 CO 3 in 10.0 mL of solution First convert to liters of solution

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10 Molarity Examples 11. Calculate the molarity of each of the following solutions. a. 8.90 g of H 2 SO 4 in 100.0 mL of solution First we need to know how many moles of H2SO4 we have Find Molar Mass of H2SO4 H 2 x 1.00794 g/mol= 2.016 g/mol S 1 x 32.066 g/mol = 32.066 g/mol O4 x 15.9994 g/mol = 63.998 g/mol Molar mass of H 2 SO 4 = 98.080 g/mol

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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 12.0107 g/mol= 72.0642 g/mol H 12 x 1.00794 g/mol= 12.0953 g/mol O 6 x 15.9994 g/mol = 95.9964 g/mol Molar mass of C 6 H 12 O 6 =180.1559 g/mol Find moles of C 6 H 12 O 6

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12 Molarity Example (continued)

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13 Molarity Examples How many grams of solute are needed to prepare each of the following solutions? a. 2.00 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 22.989770 g/mol= 22.9898 g/mol H 1 x 1.00794 g/mol= 1.0079 g/mol O 1 x 15.9994 g/mol = 15.9994 g/mol Molar mass of NaOH = 39.9971 g/mol Board

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

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

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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?

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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

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

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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 + 475 g of water = 500. g = 5.00 % NaCl solution

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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

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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

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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

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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

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

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