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Solution Concentration

Solution Concentration. Concentration: a measure of how much solute is dissolved in a specific amount of solvent or solution Concentration may be described qualitatively using the words concentrated or dilute

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Solution Concentration

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  1. Solution Concentration • Concentration: a measure of how much solute is dissolved in a specific amount of solvent or solution • Concentration may be described qualitatively using the words concentrated or dilute • Concentration expressed as a percent is a ratio of a measured amount of solute to a measured amount of solution • Percent by mass usually describes solutions in which a solid is dissolved in a liquid

  2. Solution Concentration • Percent by mass equation: • The mass of the solution equals the sum of the masses of the solute and the solvent • Percent by volume usually describes solutions in which both solute and solvent are liquids mass of solute mass of solution X 100 Percent by mass =

  3. Solution Concentration • Percent by volume equation: • The volume of the solution is the sum of the volumes of the solute and the solvent • How much water is in 70% isopropyl alcohol? volume of solute volume of solution Percent by volume = X 100

  4. MOLARITY • Molarity (M) is the number of moles of solute dissolved per liter of solution • Molarity is also known as molar concentration • A liter of solution containing one mole of solute is a 1M solution, which is read as a one molar solution. • A liter of solution containing 0.1 mole of solute is a 0.1M solution • To calculate a solution’s molarity, you must know the volume of the solution and the amount of dissolved solute

  5. MOLARITY • Calculating Molarity: • Suppose you need to calculate the molarity of 100.0 mL of an aqueous solution containing 0.085 mole of dissolved potassium chloride (KCl). You would first convert the volume of the solution from milliliters to liters using the conversion factor 1 L = 1000 mL moles of solute liters of solution Molarity (M) =

  6. MOLARITY • Conversion: • Then, to determine the molarity, you would divide the number of moles of solute by the solution volume in liters. 1 L 1000 mL 100 mL X = 0.1000 L 0.085 mol KCl 0.1000 L solution 0.85 mol L = = 0.85M

  7. MOLAR SOLUTIONS • How many grams of sucrose (C12H22O11) are in 1.50M aqueous solution of sucrose? • What if you only needed 100 mL of a 1.50M solution of sucrose for an experiment. How much sucrose do you need to use? 1.50 mol C12H22O11 1 L solution 342 g C12H22O11 1 mol C12H22O11 513 g C12H22O11 1 L solution X =

  8. MOLAR SOLUTIONS • Conversion: 1L 1000 mL 513 g C12H22O11 1 L solution X 100 mL X = 51.3 g C12H22O11

  9. MOLALITY • The volume of solution changes with temperature as it expands or contracts. • This change in volume alters the molarity of the solution. Why? • Masses donot change with temperature • Because of this, it is sometimes more useful to describe solutions in terms of how many moles of solute are dissolved in a specific mass of solvent (molality)

  10. MOLALITY • Molality (m)– the ratio of the number of moles of solute dissolved in one kilogram of solvent • The unit m is read as molal • Ex. What is the molality of a solution containing 10.0 g Na2SO4 dissolved in 1000.0 g of water? moles of solute kilogram of solvent moles of solute 1000 g of solvent Molality (m) = =

  11. MOLALITY • You must first find the moles of Na2SO4 • Once you have found the number of moles, you can now calculate the molality 1 mol 142.04 g mol Na2SO4= 10.0g Na2SO4 X = 0.0704 mol Na2SO4 0.0704 mol Na2SO4 1000.0 g H2O molality = = 0.0704m

  12. Diluting Solutions • Suppose you want to make a solution with a new concentration (molarity) from an existing solution of a given concentration (molarity), how would you do this? • You would use the following equation: M1V1 = M2V2 M1 = molarity of stock solution (original) V1 = volume of stock solution (original) M2 = molarity of diluted solution (new) V2 = volume of diluted solution (new)

  13. Diluting Solutions • What volume of a 3.00M KI solution would you use to make 0.300L of a 1.25M KI solution? M1V1 = M2V2 (3.00M)(V1) = (1.25M)(0.300L) (V1) = 0.125L

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