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Solutions Part II DHS Chemistry Chapter 15

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I. Concentrations of Solutions The concentration of a solution is a measure of the amount of solute that is dissolved in a given quantity of solvent. Amount of solute vs. amount of water

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Dilute vs Concentrated Little solute a lot of solute

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Very Concentrated

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Less Concentrated

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Concentrated solutions A concentrated solution is one that contains a high concentration of solute.

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Dilute solutions A dilute solution contains a small concentration of solute.

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Pictorial Representation

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There are several ways to express concentration. These include: percent solutions (by volume or mass), molarity, or molality.

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A. Percent Solutions

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Percent Solutions % solute = amount of solute _ 100 TOTAL amount of solvent solution 3 types: (%m/m) same units (%v/v) same units (%m/v) needs to be g/mL

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How much vinegar is just acetic acid? 5% of vinegar is acetic acid

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Percent by Volume % by volume (% (v/v)) = volume of solute 100 Volume of solution units must be the same Tip: watch out for the wording. You may need to add the volume of the solute and solvent to get the volume of the total solution (solute + solvent)

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Percent by Mass % by mass (% (m/m)) = mass of solute 100 mass of solution *units must be the same Tip: watch out for the wording. You may need to add the mass of the solute and solvent to get the volume of the total solution (solute + solvent)

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Percent Mass by Volume % mass by volume (% (m/v) = mass of solute (g) 100 volume of solution (mL) *units must g/mL

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Ex 1: 20 mL of alcohol is diluted with water to a total volume of 65 mL. What is the percentage of alcohol, by volume? %(v/v) = Volume of solute 100 Volume of solution %(v/v)= 20 mL alcohol mL H 2 O ? % = 30.8% Alcohol by volume

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65 mL alcohol + water 30.8% of this solution is alcohol. The rest is water. 20 mL alcohol

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Is white gold really gold? White Gold, 18 Karat Au 75% - Pt or Pd 25% Solute = platinum or palladium Solvent = gold

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If I had an 18k white gold ring that weighed 20g, how much of the ring isnt pure gold? White Gold, 18 Karat Au 75% - Pt or Pd 25% 25% = ?g g 5 grams of my ring isnt pure gold.

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Ex 2 : A solution containing 7 g of NaCl in 165 g of solution. What is the percent of NaCl by mass? 7 g NaCl g solution ? % NaCl (m/m) = 4.24% Solution = Solute + solvent Solution = 7 g g 158 g of solvent (water)

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Childrens Dose vs Adult Dose Diphenhydramine hydrochloride (active ingredient in allergy medicine like Benadryl)

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How do you feed a child medicine when one tablet is too strong?

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Liquid dose for children has been diluted to 12.5 mg for every 5 mL of medicine

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What percent by mass of diphenhydramine hydrochloride is in the solution? Liquid dose for children has been diluted to 12.5mg for every 5mL of medicine.0125 g =.250% (m/v) 5 mL 100

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EX 3: A saline solution containing 3.5 g of NaCl in 62.5 mL of solution. What is the percent of NaCl, by mass. 3.5 g NaCl mL solution ? % = 5.60%

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EX 3: A saline solution containing 3.5 g of NaCl in 62.5 mL of solution. What is the percent of NaCl, by mass. 3.5 g NaCl mL solution ? % = 5.60%

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Ex 4: What volume of ethanol is needed to produce 120 mL of a 22.3% (v/v) ethanol solution? %(v/v)= ethanol by volume (v/v) ? mL ethanol mL solution 22.3 % = 26.8 mL

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Ex 5: What volume of a 2.8% (m/v) glucose solution would you need to deliver to a patient who needs 750 mg of glucose? glucose by volume (m/v) g glucose 100 ? mL glucose solution 2.8 % = 26.8 mL

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Practice 1.If 10 mL of pure acetone is diluted with water to a total solution volume of 200 mL, what is the percent by volume of acetone in the solution? 2. A bottle of hydrogen peroxide is labeled 3.0% (v/v). How many mL of H 2 O 2 are in a mL bottle of this solution? 3. Calculate the grams of solute required to make 250 g of 0.10% MgSO 4 (m/m). 4. A solution contains 2.7 g CuSO 4 in 75 mL of solution. What is the percent (m/v) of the solution?

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1.If 10 mL of pure acetone is diluted with water to a total solution volume of 200 mL, what is the percent by volume of acetone in the solution? %(v/v)= acetone by volume (v/v) 10 mL acetone mL solution ? % = 5.00 %

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2. A bottle of hydrogen peroxide is labeled 3.0% (v/v). How many mL of H 2 O 2 are in a mL bottle of this solution? %(v/v)= H 2 O 2 by volume (v/v) ? mL H 2 O mL solution 3.00 % = 12.0 mL

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3. Calculate the grams of solute required to make 250 g of 0.10% MgSO 4 (m/m). %(m/m)= MgSO 4 by volume (v/v) ? g MgSO g solution 0.10 % = g

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4. A solution contains 2.7 g CuSO 4 in 75 mL of solution. What is the percent (m/v) of the solution? %(m/v)= CuSO 4 by volume (m/v) 2.7 g CuSO mL solution ? % = 3.60 %

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Practice 1.If 10 mL of pure acetone is diluted with water to a total solution volume of 200 mL, what is the percent by volume of acetone in the solution? 2. A bottle of hydrogen peroxide is labeled 3.0% (v/v). How many mL of H 2 O 2 are in a mL bottle of this solution? 3. Calculate the grams of solute required to make 250 g of 0.10% MgSO 4 (m/m). 4. A solution contains 2.7 g CuSO 4 in 75 mL of solution. What is the percent (m/v) of the solution? 5.00% acetone (v/v) 12.0mL H 2 O g MgSO % (m/v)

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B. Molarity

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Molarity Molarity (M) is the number of moles of a solute dissolved per liter of solution.

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Molarity Molarity is also known as molar concentration and is read as __#__ molar (Ex. a 2M HCl solution is read as two molar HCl Note that the volume involved is the total volume of solution, not just the solvent.

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Molarity Molarity (M) = moles of solute M =mol Liters of solution 1 L *if given grams, convert if to moles using the molar mass of the substance

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Why are grams important? You can not directly measure moles, you must calculate the mass in grams first Grams Moles Molar mass ___g = 1 mole

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How to Prepare a Solution To make 1.00 liter of a 1.00 molar (1.0 M) solution: 1) add 1.0 mol of solute to a volumetric flask 2) add about ¼ flask of distilled water. Swirl the flask till the solute is dissolved. 3) slowly add water until the final volume reads 1.00 L

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Molarity EX 1. What is the molarity of a solution that contains 8 moles of CaCl 2 in 50 mL of solution? M = 1 mol L 8 mol 0.05 L 160M CaCl 2

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Molarity EX 2. How many grams of NaCl are needed to make 500mL of a 0.2 M solution? M = 1 ? mol L.2 M 0.5 L.1 mol 0.1 mol NaCl 1 mol NaCl g NaCl=5.84 mol NaCl

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Using Molarity Ex 3: A saline solution contains 0.90 g NaCl in exactly 100 mL of solution. What is the molarity of the solution? 0.90g NaCl x 1 mol NaCl g NaCl = mol NaCl 100 mL x 1 L 1000 mL = L NaCl Step 1: Calculate # moles Step 2: mL L

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Ex 3 continued Step 3: Calculate Molarity M = mol L ? M 0.1 L M

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Ex 2: How many grams of solute are present in 562 mL of 0.24 M Na 2 SO 4 ? M = mol mol = M L L mol = 0.24M Na 2 SO 4 x.562L = 0.135mol

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Convert from Moles to Grams 0.135mol Na2SO4 | 142g Na 2 SO 4 = | 1 mol Na 2 SO 4 = 19.2g Na 2 SO 4

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Practice 1.A solution has a volume of 2.0 L and contains 36.0 g of glucose. If the molar mass of glucose is 180 g/mol, what is the molarity of the solution? 0.100M glucose 2. How many moles of ammonium nitrate are in 335 mL of M NH4NO3? 0.142mol NH 4 NO 3 3. How many grams of solute are in 250 mL of 2.0 M CaCl 2 solution? 55.5gCaCl 2 4. Describe how you would prepare 250 mL of a 0.2 M NaOH solution. Need 2.00g NaOH in 250mL of solution

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1. A solution has a volume of 2.0 L and contains 36.0 g of glucose. If the molar mass of glucose is 180 g/mol, what is the molarity of the solution? Molarity = mol L Glucose = C 6 H 12 O 6 Molar mass = 6(12.01g) + 12(1.008g) + 6(15.999g) = Calculate moles: 36.0g C 6 H 12 O 6 | 1 mol C 6 H 12 O 6 = mol C 6 H 12 O 6 | XXX g C 6 H 12 O 6 Calculate Molarity:XXXmol C 6 H 12 O 6 = 0.100M glucose 2.0 L

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C. Dilutions

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You can make a less concentrated solution by diluting it with solvent. The dilution reduces the grams of solute per unit volume, but the total amount of solute in solution does not change.

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Diluted Solutions Before After Dilutions

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Moles of solute before dilution = Moles of solute after dilution Moles of solute = Molarity x volume Dilutions: M 1 V 1 = M 2 V 2

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Ex: How many mL of a stock solution of 2.00 M MgSO 4 would you need to prepare mL of M MgSO 4 ? (2M)(V 1 ) = ( 0.400M)(100mL) m 1 v 1 m 2 v 2 V 1 = 20mL of stock solution Stock soln

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Ex. 2: Describe how to prepare 100 mL of 0.400M MgSO 4 from 2M MgSO 4. (see previous example) Add 20mL of 2M stock solution in a container and add solvent up to the 100mL mark

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Practice 1. How many mL of a stock solution of 4.00 M KI would you need to prepare mL of M KI? 47.5mL of 4.00MKI 2. What volume must you dilute to make 50.0 mL of 0.20 M KNO 3 from 4.0 M KNO 3 ? 2.5mL of 4M KNO 3 3. What is the molarity of a solution formed when you add 200 mL of water to 50 mL of 5.0 M HCl? 1.00M

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1. How many mL of a stock solution of 4.00 M KI would you need to prepare mL of M KI? (4M) (V1) = (0.760M) (250mL) m1 v1 m2 v2 V1 = 47.5mL of 4M stock solution

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2. What volume must you dilute to make 50.0 mL of 0.20 M KNO 3 from 4.0 M KNO 3 ? (4M) (V1) = (0.20M) (50mL) m1 v1 m2 v2 V1 = 2.5mL of 4M solution

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3. What is the molarity of a solution formed when you add 200 mL of water to 50 mL of 5.0 M HCl? (5.0M) (50mL) = (M2) (250mL) m1 v1 m2 v2 M2 = 1M of solution

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EX. A chemist starts with 50 mL of a 0.40M NaCl solution and dilutes it to 1000 mL. What is the concentration of the dilute solution? (0.4 M)(50 mL) = ( ?M)(1000 mL) M 1 V 1 M 2 V 2 M 2 = M is the concentration of the diluted solution Stock soln

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Practice 1)What volume of a 3.00M KI stock solution would you use to make L of a 1.25 M KI solution?0.125 L 2)How many milliliters of a 5.0M H 2 SO 4 stock solution would you need to prepare mL of a 0.25M H 2 SO 4 ? 5.00 mL 3)If you dilute 20.0 mL of a 3.0M solution to make mL of solution, what is the molarity of the dilute solution? 0.600M

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Practice 1 (3.00M) (V 1 ) = (1.25M) (.300) m1 v1 m2 v2 V 1 =.125 L of 3M stock solution Practice 2 (5M) (V 1 mL) = (0.25M) (100 mL) m1 v1 m2 v2 V 1 = 5.00mL of 5M solution

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Practice 3 (3.0M) (20mL) = (M 2 ) (100mL) m 1 v 1 m 2 v 2 M 1 = 0.600M is the new concentration

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