Laboratory Solutions

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.

3. Concentrations • weight per volume • Percents • Molarity

4. Weight per Volume

5. 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.

7. Solute • The substance that is being dissolved • NaCl

8. Solvent • The liquid in which the solute is dissolved. • Water

9. Amount vs. Concentration • Amount is how much substance is present. • Concentration is ratio with a numerator (amount) and a denominator (usually volume)

10. Proportions 1mg = 10mg 10 mL 100mL

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 300 mL 300 mL x 10 g = ? 100 mL . 30 g = ?

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 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.

20. 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

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. 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

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 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.

30. 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 solution Volume % = 20.0 mL of solute x 100 1000mL of solution Volume % = 2%

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. 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

36. 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.

42. 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% glucose 149.8 g solution

43. 20. What is the weight percent of sucrose in a solution made by dissolving 29.89 g of sucrose in 1000 g of water?

44. 21. What is the weight percent of NaCl in a solution made by dissolving 123.5 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. 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

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 3.0% 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