1. Solutions and Units of Measure

2. Today’s Laboratory Objectives To learn how to make solutions properly To learn how to make solutions properly To learn how to use an autoclave To learn how to use an autoclave To learn how to operate a pipetman properly To learn how to operate a pipetman properly

3. Definition of a Solution A Solution consists of two components: 1) the solvent or dissolving medium 2) solute or substance to be dissolved Define Solutions as: 1) “Concentrated” = a relatively large amount of solute per unit volume of solvent 2) “Weak” solution = a relatively small amount of solute per unit volume of solvent

4. Methods for Expressing the Concentration of a Solution 1.Molarity: = No. Moles of solute Liters of solvent Liters of solvent 2.Molality: = No. Moles of solute 1000 g solvent 1000 g solvent 3.Percentage by Weight = Weight of solute x 100 by Weight = Weight of solute x 100 Weight of solvent Weight of solvent by Volume = Volume of solute x 100 by Volume = Volume of solute x 100 Volume of solvent Volume of solvent 4.Normality = No. of equivalents of solute Liters of solvent Liters of solvent

5. Guildelines for Making Solutions Use highest grade reagents available. Be careful not to contaminate stock reagents Prepare all solutions with high quality water, at least deionzed, but preferably with nano-pure. Whenever possible, sterilize all solutions by autoclaving or by filtration through a 0.22 um filter

6. Making a Solution 1.Weigh out the needed amount of solute 2.Add most, but not all of the required solvent to dissolve the solute

7. Making a Solution 3.Adjust the pH while stirring the solution a.Acids or bases are used to adjust the pH b.Specific acid or base used is important -use acids or bases that contain the same ions present in solution c.If heat is required to get a solute into solution the solution must be cooled prior to adjusting the pH 4.Bring to Final Volume

8. Making Solutions from a Concentrated Solution C 1 V 1 = C 2 V 2 where: C 1 = initial concentration C 2 = final concentration C 2 = final concentration v 1 = initial volume v 2 = final volume

9. Using a Pipetman To Draw Up A Solution 1. Attach a tip to the shaft of the pipetman without touching the end of the tip 2. Depress the plunger to the first stop 3. Holding the pipetman vertically, immerse the untouched portion of the tip into the liquid sample 4. Allow the plunger to return slowly to the up position. Do not allow it to snap up Do not allow it to snap up 5. Carefully withdraw the tip from the sample liquid and rim the tip if necessary tip if necessary

10. To Dispense a Solution Using a Pipeman 1. Place the tip end again the wall of the receiving vessels and depress the plunger slowly to the first stop 2. Wait for a second or two and then push the plunger through the second stop to expel any residual liquid 3. With the plunger fully depressed, withdraw the pipetman from the vessel carefully 4. Allow the plunger to return to the top position