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Published byAllan Leonard Modified over 9 years ago

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Laboratory Solutions

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Solute The substance that is being dissolved NaCl

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Solvent The liquid in which the solute is dissolved. Water

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Percentage Concentrations

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Weight/Volume Percent Weight/Volume % = grams of solute x 100 volume of solution A weight per volume percent concentration is the weight of the solute in grams per 100 mL of solution. It can be abbreviated as w/v.

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A student adds 20.0 grams of NaCl to volumetric flask and fills it to the 100mL mark. What is the weight per volume (w/v) percent concentration of the solution? Weight % = grams of solute x 100 volume of solution Weight % = 20.0 grams x 100 100mL of solution Weight % = 20% NaCl solution

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How many grams of NaCl would be needed to prepare 500 ml of a 5% solution of NaCl? Grams of solute = Volume of solution x Weight % Grams of solute = 500mL x 5% Grams of solute = 500mL x 5g/100mL Grams of solute = 25 g of NaCl

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Volume/Volume Percent volume % = volume of solute x 100 volume of solution Volume % = mL of solute x 100 100 mL of solution In a percent by volume expression, both the amount of solute and the total solution are expressed in volume units. It can be abbreviated as v/v.

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A student adds 20.0 ml of ethanol to a volumetric flask and fills it to the 1L mark. What is the percent volume (v/v) concentration of the solution? Volume % = volume of solute x 100 volume of solution Volume % = 20.0 mL of solute x 100 1000mL of solution Volume % = 2%

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How many milliliters of ethanol would you need to make 10.0 mL of a 10% by volume solution of ethanol in water? volume of solute = Volume of solution x Volume /volume % volume of solute = 10.0 ml x 10% volume of solute = 1.0 ml ethanol

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Weight Percent Weight % = weight of solute weight of solution x 100 In a Weight (mass) Percent the numerator is the mass of solute and the denominator is mass of total solution.

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What is the weight percent of glucose in a solution made by dissolving 4.6 g of glucose in 145.2 g of water? Determine total weight of solution: 4.6 g glucose + 145.2 g water 149.8 g solution Calculate Weight % glucose = 4.6 g glucose x 100 = 3.1% glucose 149.8 g solution

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20. What is the weight percent of sucrose in a solution made by dissolving 29.89 g of sucrose in 1000 g of water? 29.89 + 1000 = 1029.98 solution 29.89/1029.98 x 100 = 2.90 %

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How much NaCl would you need to prepare 400 g of a 2.50% solution of sodium chloride? Grams of solute = Gram of solution x Weight/Weight % Grams of solute = 400 g x 2.50 % Grams of solute = 10.0 g salt

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Homework Problems

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1. A chemist adds 78.5 grams of MgCl2 to volumetric flask and fills it to the 1L line. What is the weigh per volume percent of the solution? Weight % = grams of solute x 100 volume of solution Weight % = 78.5 g x 100 1000mL of solution 7.85 %

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2. How many grams of NaCl would be needed to prepare 600 ml of a 34% solution? Grams of solute = Volume of solution x W/V % Grams of solute = 600ml x 34 % 204 grams NaCl

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3. How many grams of KCl would be needed to prepare.4 L of a 25% solution? 400 mL x 25% 100 grams KCl

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4. How many grams would be needed to prepare an 11% solution of sucrose in 350 ml? 350 x 11% 38.5 grams

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5. Find amount of milligrams present in: 75 mL CaCo 3 solution with a concentration of 3 mg/ml. 75ml x 3mg/ml 225mg

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6. A student adds 20 ml of methanol to 400ml flask and fills it to the mark. What is the percent per volume (v/v) concentration of the solution? 20ml/400ml x 100 5%

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7. 37ml of a substance is put into a 500 ml flask filling it. What is the v/v concentration of the solution? 37 ml/500ml x 100 7.4%

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8. 50 ml of a substance is added into a 1.25 L flask, filling it. What is the percent volume concentration of the solution? 50ml/1250 x 100 4%

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9. How many milliliters of ethanol would you need to make 100 mL of a 23% by volume solution? 100ml x 23ml/100ml 23 ml ethanol

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10. What is the weight percent of NaCl in a solution made by dissolving 480 g of NaCl in 1000 g of water? Weight % = weight of solute weight of solution x 100 480/1480 x 100 32.43%

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11. How much MgCO 3 would you need to make 120g of an 8.5% solution of MgCO 3 ? 120g x 8.5% 10.2g

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12. What is the weight percent of sucrose in a solution made by dissolving 50 g in 350 g of water? Weight % = weight of solute weight of solution x 100 50g/ 400g x 100 12.5%

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