1. Laboratory Solutions
In the laboratory, we will be using different concentration of chemical solutions. Each protocol will require different solutions in varying concentrations.
Revised 9/06/2006

2. 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.
Seidman, Lisa A., and Cynthia J. Moore. Basic Laboratory Methods for Biotechnology. Upper Saddle River: Prentice Hall, 2000.

3. Concentrations
weight per volume
Percents
Molarity

4. Weight per Volume

5. volume volume of solution
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 

6. 2g NaCl 1L
Means that 2 g of NaCl is dissolved in enough liquid so that the total volume is 1L.
Seidman, Lisa A., and Cynthia J. Moore. Basic Laboratory Methods for Biotechnology. Upper Saddle River: Prentice Hall, 2000.

7. Solute The substance that is being dissolved NaCl
Seidman, Lisa A., and Cynthia J. Moore. Basic Laboratory Methods for Biotechnology. Upper Saddle River: Prentice Hall, 2000.

8. Solvent The liquid in which the solute is dissolved. Water
Seidman, Lisa A., and Cynthia J. Moore. Basic Laboratory Methods for Biotechnology. Upper Saddle River: Prentice Hall, 2000.

9. Amount vs. Concentration
Amount is how much substance is present.
Concentration is ratio with a numerator (amount) and a denominator (usually volume)
Seidman, Lisa A., and Cynthia J. Moore. Basic Laboratory Methods for Biotechnology. Upper Saddle River: Prentice Hall, 2000.

10. Proportions 1mg = 10mg 10 mL 100mL
Seidman, Lisa A., and Cynthia J. Moore. Basic Laboratory Methods for Biotechnology. Upper Saddle River: Prentice Hall, 2000.

11. 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 mL
300 mL x 10 g = ?
100 mL
30 g = ?
Seidman, Lisa A., and Cynthia J. Moore. Basic Laboratory Methods for Biotechnology. Upper Saddle River: Prentice Hall, 2000.

12. Question
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?

13. 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?

14. Question
3. How many milligrams of NaCl are present in 50 mL of a solution that has a concentration of 2mg/mL NaCl?

15. Question
If the concentration of MgSO4 in a solution is 25 g/L, how much magnesium sulfate is present in 100mL of this solution?

16. Question
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?

17. Percentage Concentrations

18. 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

19. Weight/Volume Percent
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.
Weight/Volume % = grams of solute x 100
volume of solution

20. Weight % = grams of solute x 100 volume of solution
Example 2 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 volume of solution
Weight % = grams x mL of solution
Weight % = % NaCl solution

21. 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?

22. 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?

23. 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 %

24. Grams of solute = 500mL x 5g/100mL Grams of solute = 25 g of NaCl
Example 3 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

25. 8. How many grams of NaCl would be needed to prepare 250 ml of a 5% solution of NaCl?

26. 9. How many grams of Glucose would be needed to prepare 200 ml of a 2% solution of glucose?

27. 10. How many grams of EDTA would be needed to prepare 475 ml of a 15% solution of EDTA?

28. 11. How many grams of Pb(NO3)2 would be needed to prepare 500 ml of a 5% solution of Pb(NO3)2?

29. Volume/Volume Percent
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.
volume % = volume of solute x volume of solution
Volume % = mL of solute x mL of solution

30. Example 4 A 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 solution
Volume % = mL of solute x 100
1000mL of solution
Volume % = %

31. 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?

32. 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?

33. 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?

34. 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 %

35. volume of solute = 1.0 ml ethanol
Example 5 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

36. 15. How many milliliters of ethanol would you need to make 20
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 %

37. 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 %

38. 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 %

39. 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 %

40. 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 %

41. 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.
Weight % = weight of solute weight of solution x 100

42. Example 6: What is the weight percent of glucose in a solution made by dissolving 4.6 g of glucose in g of water?
Determine total weight of solution:
4.6 g glucose g water g solution
Calculate Weight % glucose =
  4.6 g glucose x 100 = 3.1% glucose
149.8 g solution
Example 1-a  asks, "What is the weight percent of glucose in a solution made by dissolving 4.6 g of glucose in g of water?" The way that I recommend you go about doing this is to look at what you need to find, look at what you are given, and determine what the relationship is. Let's start with what you are trying to find, the weight percent of glucose in the solution. What do we need in order to calculate that? We need to divide the weight of glucose by the weight of the solution. We have the weight of glucose, that is 4.6 g. What about the weight of the solution? That is not given, but we can figure it out by adding together the weight of glucose and water to get g. Now we can calculate the weight percent of glucose as shown to get 3.1%.

43. 20. What is the weight percent of sucrose in a solution made by dissolving g of sucrose in 1000 g of water?

44. 21. What is the weight percent of NaCl in a solution made by dissolving g of NaCl in 898 g of water?

45. 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 %

46. Grams of solute = 400 g x 2.50 % Grams of solute = 10.0 g salt
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
The next question is a little bit different. You are asked how you would prepare 400 g of a 2.50% solution of salt. You are given 400 g of solution (that is total) and you know that 2.50% of that is going to be salt. You need to find out how much salt you need and how much water you need. You can simply multiply 400 g by 2.50% to find out how much salt there is (shown in the top line), or you can set up the calculation shown on the next line. Either way, you find that you need 10.0 g of salt. Since you need a total mass of 400 g and 10 g of that is salt, the remaining 390 g would have to be water. So, to prepare this solution you would have to mix 10.0 g of salt with 390 g of water.

47. 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 %

48. 23. How much AgNO3 would you need to prepare 150 g of a 3
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 %

49. 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 %

50. Homework Problems

51. 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 volume of solution
Weight % = g x mL of solution

52. 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 %

53. 3. How many grams of KCl would be needed to prepare
3. How many grams of KCl would be needed to prepare .4 L of a 25% solution?

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

55. 5. Find amount of milligrams present in: 75 mL CaCO3 solution with a concentration of 3 mg/ml.

56. 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?

57. 7. 37ml of a substance is put into a 500 ml flask filling it
7. 37ml of a substance is put into a 500 ml flask filling it. What is the v/v concentration of the solution?

58. 8. 50 ml of a substance is added into a 1. 25 L flask, filling it
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?

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

60. 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

61. 11. How much MgCO3 would you need to make 120g of an 8
11. How much MgCO3 would you need to make 120g of an 8.5% solution of MgCO3?

62. 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