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MIXTURES & SOLUTIONS Today you need: Materials to take notes

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SC7. Students will characterize the properties that describe solutions and the nature of acids and bases. a. Explain the process of dissolving in terms of solute/solvent interactions b. Observe factors that effect the rate at which a solute dissolves in a specific solvent, c. Express concentrations as molarities, d. Prepare and properly label solutions of specified molar concentration, e. Relate molality to colligative properties. The GPS Standard

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SOLUBILITY Solubility maximum grams of solute that will dissolve maximum grams of solute that will dissolve in 100 g of solvent at a given temperature in 100 g of solvent at a given temperature varies with temperature varies with temperature based on a saturated solution based on a saturated solution

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SOLUBILITY SATURATED SOLUTION no more solute dissolves UNSATURATED SOLUTION more solute dissolves SUPERSATURATED SOLUTION becomes unstable, crystals form increasing concentration

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SOLUBILITY CURVES solids Solubility of solids increase with increases in temperature. gases Solubility of gases in liquids decrease with increasing temperature WHY?

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THE EFFECT OF TEMPERATURE ON SOLUBILITY IS DEPENDENT ON THE PHASE OF MATTER. ToTo S ToTo S Solids or liquids dissolved in liquids Gases dissolved in liquids As T o, solubility

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WHAT IS THE SOLUBILITY OF____ AT ____°C?

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SOLUTION CONCENTRATION

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THINK ABOUT IT… you probably are familiar with the difference between what is called a "weak" solution or a "strong" solution.

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CONCENTRATION … The measure of how much solute is dissolved in a specific amount of solvent or solution. a measure of solute-to-solvent ratio concentrated vs. dilute lots of solute not much solute watery Add water (hydrate) to dilute remove water (evaporate by boiling) to concentrate

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CONCENTRATIONS Qualitative (words): -Concentrated -dilute Quantitative (numbers): -percent by mass -percent by volume -Molarity (M) -molality (m)

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WHAT IS THE [SOLID SOLUTE] IN A LIQUID SOLVENT? WHAT PART? OUT OF WHAT WHOLE? Read the above as: What is the concentration of solid solute in a liquid solvent?

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Percent by mass = mass of solute x 100 mass of solution PERCENT BY MASS Mass of solution =mass of solute + mass of solvent Use when combining a solid solute into a liquid solvent Mass of Solvent?

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FINDING MASS OF SOLVENT Or finding the mass of a volume. Is there a relationship b/w mass and volume? -- Density or D -- D = m/V or m = DV Since our solvent is H 2 O and we know that the D H2O = 1.0 g/ml (constant) So, m = DV or m = (1.0 g/ml) (V)

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EXAMPLE PERCENT BY MASS: To maintain a sodium chloride (NaCl) concentration similar to ocean water, an aquarium must contain 3.6 g NaCl per g of water. What is the percent by mass of NaCl in the solution? Given: Mass of solute: 3.6 g NaCl Mass of solvent: g H 2 O Equation: Percent by mass = mass of solute x 100 mass of solution = 3.6 g NaCl x g NaCl g H 2 O = 3.5 %

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What is the percent by mass of NaHCO 3 in a solution containing 20.0 g of NaHCO 3 dissolved in mL of H 2 O?

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BUT WHAT IF THE SOLUTE AND SOLVENT ARE BOTH LIQUIDS?

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What does this mean?

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PERCENT BY VOLUME volume of solute Percent by volume = x 100 volume of solution

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TRY CALCULATING PERCENT BY VOLUME: What is the percent by volume of ethanol in a solution that contains 35 mL of ethanol dissolved in 155 mL of water? Percent by volume = volume of solute x 100 volume of solution volume of solution

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How much isopropyl alcohol is actually in a 473 mL solution of 99 % isopropyl alcohol? Percent by volume = volume of solute x 100 volume of solution volume of solution

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MOLARITY Molarity (M) = moles of solute Liters of solution The unit M is read, molar

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What is the molarity of an aqueous solution containing 0.22 mol of glucose (C 6 H 12 O 6 ) in 1.5 L of solution? CALCULATING MOLARITY:

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A mL solution contains 5.10 g of glucose (C 6 H 12 O 6 ). What is the molarity of this solution? (The molar mass of glucose is g/mol.)

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Remember, Molarity is just a measure of how concentrated a solution is (or how strong it is)… so, Which is the most concentrated solution? a) 0.50 M CuSO 4 b) 1.75 M CuSO 4 c) 3.00 M CuSO 4 d) 7.00 M CuSO 4

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Which is the least concentrated solution? a) 0.25 M HCl b) 0.75 M HCl c) 2.00 M HCl d) 4.25 M HCl

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We know from Guy Lussacs Law that V of a solution changes with T. This change in V alters the M of the solution. We also know that mass does not change with T. So, sometimes it is more useful to describe solutions in terms of how many moles of solute are dissolved in a specific mass of solvent.

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MOLALITY Molality (m) = moles of solute kg of solvent You LOVE me!! The unit m is read, molal

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CALCULATING MOLALITY: In the lab, a student adds 4.5 g of sodium chloride (NaCl) to 0.1 kg of water. Calculate the molality.

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What is the molality of a solution containing 10.0 g of Na 2 SO 4 dissolved in g of water?

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In the lab, you might use concentrated solutions of standard molarities, called stock solutions. But, you can prepare a less-concentrated solution by diluting the stock solution with additional solvent.

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MAKING A DILUTE SOLUTION initial solution remove sample diluted solution same number of moles of solute in a larger volume mix moles of solute

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DILUTION Preparation of a desired solution by adding water to a concentrate. Moles of solute remain the same. M = Molarity (Concentration), V = volume

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Dilution Equation: M 1 V 1 = M 2 V 2 M 1 and V 1 represent the molarity and volume of the stock solution, while M 2 and V 2 represent the molarity and volume of the dilute solution.

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So for instance, what volume, in mL, of a 2.00M calcium chloride (CaCl 2 ) stock solution would you use to make 0.50 mL of 0.300M calcium chloride solution?

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What volume of a 3.00M KI stock solution would you use to make L of a 1.25M KI solution?

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CONCENTRATION THE AMOUNT OF SOLUTE IN A SOLUTION A. % mass = mass of solute mass of soln B. % volume = V of solute V of soln C. molarity (M) = moles of solute L of soln – used most often in this class D. molality (m) = moles of solute kg of solvent M = mol L % by mass – medicated creams % by volume – rubbing alcohol E. M 1 V 1 = M 2 V 2 dilutions

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