laboratory solutions in the laboratory, we will be using different concentration of chemical...
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Laboratory SolutionsIn the laboratory, we will be using different concentration of chemical solutions. Each protocol will require different solutions in varying concentrations.
Revised 9/06/2006
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Concentration• The amount of a particular
substance in a stated volume (or sometimes mass) of a solution or mixture.
• Ratio where the numerator is the amount of the material of interest and the denominator is the volume or mass of the entire mixture.
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Concentrations
•weight per volume•Percents
•Molarity
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Weight per Volume
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Weight per Volume• The simplest way to represent
concentration of a solution is as the mass in grams per unit of volume.
Weight = mass of solute
volume volume of solution
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2g NaCl
1L• Means that 2 g of NaCl is dissolved
in enough liquid so that the total volume is 1L.
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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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Amount vs. Concentration
• Amount is how much substance is present.
• Concentration is ratio with a numerator (amount) and a denominator (usually volume)
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Proportions
1mg = 10mg
10 mL 100mL
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Example 1: How could you make 300 mL of a solution that has a concentration of 10g of NaCl in 100 mL total solution?
10 g = ?100 mL 300 mL300 mL x 10 g = ?
100 mL .30 g = ?
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Question
1. Your mother gives you 250mg of acetaminophen and a cup containing 500ml of water. What is the concentration of the solution if you dissolve the Tylenol in the water?
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Question
2. If a solution requires a concentration of 3g of NaCl in 250 mL total volume, how much NaCl is required to make 100mL?
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Question
3. How many milligrams of NaCl are present in 50 mL of a solution that has a concentration of 2mg/mL NaCl?
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Question 4. If the concentration of MgSO4 in a
solution is 25 g/L, how much magnesium sulfate is present in 100mL of this solution?
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Question5. If a solution requires .005 g of Tris
base per Liter, how much Tris Base is required to make 10-3 Liters of this solution?
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Percentage Concentrations
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Percentage Concentrations When concentration is expressed in
terms of percent, the numerator is the amount of solute and the denominator is 100 units of total solution.
• weight/volume percent • volume percent• weight percent
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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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Example 2A 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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6. A student adds 13.5 grams of KCl to volumetric flask and fills it to the 1000mL mark. What is the weight per volume percent of the solution?
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7. A student adds 45.6 grams of MgCl2 to volumetric flask and fills it to the 1000mL mark. What is the weight per volume percent of the solution?
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By rearranging the equation we can determine how much chemical we needed to add to the desired volume to prepare a solution of the correct concentration.
Grams of solute = Volume of solution x W/V %
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Example 3How 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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8. How many grams of NaCl would be needed to prepare 250 ml of a 5% solution of NaCl?
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9. How many grams of Glucose would be needed to prepare 200 ml of a 2% solution of glucose?
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10. How many grams of EDTA would be needed to prepare 475 ml of a 15% solution of EDTA?
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11. How many grams of Pb(NO3)2 would be needed to prepare 500 ml of a 5% solution of Pb(NO3)2?
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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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Example 4A student adds 20.0 ml of ethanol to 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 solutionVolume % = 20.0 mL of solute x 100
1000mL of solutionVolume % = 2%
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12. A student adds 10.0 ml of ethanol to 100mL volumetric flask and fills it to the mark. What is the percent volume (v/v) concentration of the solution?
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13. A student adds 3.5 ml of isopropanol to 50mL volumetric flask and fills it to the mark. What is the percent volume (v/v) concentration of the solution?
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14. A student adds 1.5 ml of methanol to 100mL volumetric flask and fills it to the mark. What is the percent per volume (v/v) concentration of the solution?
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By rearranging the equation we can determine the volume the chemical solution we needed to add to the desired volume to have a solution of the correct concentration.
Volume of solute = Volume of solution x Volume %
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Example 5How 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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15. How many milliliters of ethanol would you need to make 20.0 mL of a 10% by volume solution of ethanol in water?
volume of solute = Volume of solution x Volume /volume %
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16. How many milliliters of isopropyl alcohol would you need to make 100 mL of a 75% by volume solution of isopropyl alcohol in water?
volume of solute = Volume of solution x Volume /volume %
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17. How many milliliters of methanol would you need to make 1L of a 90% by volume solution of methanol in water?
volume of solute = Volume of solution x Volume /volume %
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18. How many milliliters of bleach would you need to make 1L of a 20% by volume solution of bleach water?
volume of solute = Volume of solution x Volume /volume %
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19. How many milliliters of SDS solution would you need to make 1L of a .1 % by volume solution of SDS buffer?
volume of solute = Volume of solution x Volume /volume %
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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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Example 6: 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% glucose149.8 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?
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21. What is the weight percent of NaCl in a solution made by dissolving 123.5 g of NaCl in 898 g of water?
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By rearranging the equation we can determine the mass of the chemical we needed to make the solution of the correct concentration.
Grams of solute = Gram of solution x Weight/Weight %
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Example 7: 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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22. How much KCl would you need to prepare 300g of a 25% solution of KCl?
Grams of solute = Gram of solution x Weight/Weight %
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23. How much AgNO3 would you need to prepare 150 g of a 3.0% solution of Ag NO3?
Grams of solute = Gram of solution x Weight/Weight %
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24. How much resin would you need to prepare 200 g of a 75% solution of resin in acetone?
Grams of solute = Gram of solution x Weight/Weight %
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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
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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 %
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3. How many grams of KCl would be needed to prepare .4 L of a 25% solution?
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4. How many grams would be needed to prepare an 11% solution of sucrose in 350 ml?
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5. Find amount of milligrams present in: 75 mL CaCO3 solution with a concentration of 3 mg/ml.
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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?
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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?
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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?
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9. How many milliliters of ethanol would you need to make 100 mL of a 23% by volume solution?
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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
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11. How much MgCO3 would you need to make 120g of an 8.5% solution of MgCO3?
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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