Solutions and Units of Solutions and Units of MeasureMeasure

Today’s Laboratory ObjectivesToday’s Laboratory Objectives

To learn how to make solutions properlyTo learn how to make solutions properly To learn how to use an autoclaveTo learn how to use an autoclave To learn how to operate a pipetman properlyTo learn how to operate a pipetman properly

Definition of a SolutionDefinition of a Solution

A Solution consists of two components: A Solution consists of two components: 1) the solvent or dissolving medium1) the solvent or dissolving medium2) solute or substance to be dissolved2) solute or substance to be dissolved

Define Solutions as:Define Solutions as:1) “Concentrated” = a relatively large amount of 1) “Concentrated” = a relatively large amount of

solute per unit volume of solvent solute per unit volume of solvent

2) “Weak” solution = a relatively small amount 2) “Weak” solution = a relatively small amount of solute per unit volume of solvent of solute per unit volume of solvent

Methods for Expressing the Methods for Expressing the Concentration of a Solution Concentration of a Solution

1.1. Molarity:Molarity:= = No. Moles of soluteNo. Moles of solute

Liters of solventLiters of solvent

2.2. Molality:Molality:= = No. Moles of soluteNo. Moles of solute

1000 g solvent1000 g solvent3.3. PercentagePercentage

by Weight = by Weight = Weight of solute Weight of solute x 100 x 100 Weight of solventWeight of solvent

by Volume = by Volume = Volume of soluteVolume of solute x 100 x 100 Volume of solventVolume of solvent

4.4. NormalityNormality= = No. of equivalents of soluteNo. of equivalents of solute

Liters of solventLiters of solvent

Guildelines for Making SolutionsGuildelines for Making Solutions

Use highest grade reagents available. Be careful not to Use highest grade reagents available. Be careful not to contaminate stock reagentscontaminate stock reagents

Prepare all solutions with high quality water, at least deionzed, but Prepare all solutions with high quality water, at least deionzed, but preferably with nano-pure.preferably with nano-pure.

Whenever possible, sterilize all solutions by autoclaving or by Whenever possible, sterilize all solutions by autoclaving or by filtration through a 0.22 um filterfiltration through a 0.22 um filter

Making a SolutionMaking a Solution

1.1. Weigh out the needed amount of Weigh out the needed amount of

solutesolute

2.2. Add most, but not all of the Add most, but not all of the required solvent to dissolve the required solvent to dissolve the solutesolute

Making a SolutionMaking a Solution3.3. Adjust the pH while stirring the solutionAdjust the pH while stirring the solution

a.a. Acids or bases are used to adjust the pH Acids or bases are used to adjust the pH b.b. Specific acid or base used is important -use Specific acid or base used is important -use

acids or bases that contain the same ions acids or bases that contain the same ions present in solutionpresent in solution

c.c. If heat is required to get a solute into If heat is required to get a solute into solution the solution must be cooled prior to solution the solution must be cooled prior to

adjusting the adjusting the pHpH

4.4. Bring to Final VolumeBring to Final Volume

Making Solutions from a Making Solutions from a Concentrated SolutionConcentrated Solution

CC11VV1 1 = C= C22VV22

where: Cwhere: C11 = initial concentration = initial concentration

CC22 = final concentration = final concentration

vv11 = initial volume = initial volume

vv22 = final volume = final volume

Using a Pipetman To Draw Using a Pipetman To Draw Up A SolutionUp A Solution

1.1. Attach a tip to the shaft of the pipetman without Attach a tip to the shaft of the pipetman without touching the touching the end of the tip end of the tip2.2. Depress the plunger to the first stop Depress the plunger to the first stop3.3. Holding the pipetman vertically, immerse the untouched Holding the pipetman vertically, immerse the untouched

portion of the tip into the liquid sample portion of the tip into the liquid sample 4. Allow the plunger to return 4. Allow the plunger to return slowlyslowly to the up position. to the up position. Do notDo not allow it to snap upallow it to snap up5.5. Carefully withdraw the tip from the sample liquid and Carefully withdraw the tip from the sample liquid and rim the rim the tip if necessarytip if necessary

To Dispense a Solution To Dispense a Solution Using a PipemanUsing a Pipeman

1. Place the tip end again the wall of the receiving vessels 1. Place the tip end again the wall of the receiving vessels and depress the plunger slowly to the first stop and depress the plunger slowly to the first stop

2. Wait for a second or two and then push the plunger 2. Wait for a second or two and then push the plunger through the second stop to expel any residual liquid through the second stop to expel any residual liquid

3.3. With the plunger fully depressed, withdraw the With the plunger fully depressed, withdraw the pipetman pipetman from the vessel carefully from the vessel carefully4. Allow the plunger to return to the top position4. Allow the plunger to return to the top position