Overcoming Molephobicity
(5 Steps to Teach Solution Prep)
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Ellyn Daugherty
SM Biotech Career Pathway
www.BiotechEd.com
www.emcp.com/biotech
www.sargentwelch.com/biotech
aeedaugher@aol.com
Biotech 1 SLOP
Text - Chapter 3
Lab Manual - Chapter 3
Student CD Tutorials
Course Planner
Five Steps to Teach Solution Prep
1. What is a solution?
2. Solvent Measurement
3. Measure the Solute
4. Mix the Solute and Solvent
5. Check the Solution Preparation
Step 1. What is a Solution ?
• Solutes (usually measured in g)
• Solvents (usually measured in mL)
• Mixed together until solute dissolves in
solvent
8 mg/mL
solute
concentration =
solution volume
• Described by the portion of solute to
solution volume usually in one of 3 ways:
- mass/volume
•5 g/L protease
•175 mg/mL rennin
•25 µg/µL chymosin
- % mass/volume
- molarity
• 2% glucose solution
• 10% sodium hydroxide solution
• 1M NaOH
• 50 mM TRIS
• 5 µM CaCl2
4 mg/mL
2 mg/mL
Step #2 Solvent Measurement
Volume of solvent is usually measured using one of 3
instruments. For each, ask:
• What is the total volume that can be measured?
• What is the value of each type of graduation?
graduated cylinder
pipet
micropipet
Volume and Mass Measurement
requires Metric Measurements and Conversions
1000
L
1000
mL
µL
92 mL = _________ µL
357 µL = _________ mL
0.5 g = _________ mg
0.557 mg = _________ g
Step #3 Solute Measurement
Solutes are usually dry chemicals
and their mass is measured on a
scale/balance and reported in
grams (g).
For a specified concentration of a
specified volume of solution, the
technician must determine the
amount of mass of solute needed
for the volume of solution at some
final concentration.
3 different equations, one for each
concentration units group
- mass/volume
- % mass/volume
- molarity
Determine the Mass of Solute (g)
3 different equations, one for each concentration units group
___________g/mL
concentration desired
• mass/volume
__________g/mL
• % mass/volume
____________mL
conc desired (decimal) X volume desired
_________
• molarity
X
____________mL
_________________
volume desired = mass of solute needed (g)
concentration
desired (mol/L)
____________
X
__________
_________________
=
mass of solute needed (g)
__________
volume desired X molecular weight = mass of solute needed
(L)
(g/mol)
(g)
Measuring for Mass/Volume Solutions
To make 100 mL of a 5 mg/mL hemoglobin solution
___________
_____________
___________g______
concentration desired X volume desired = mass of solute to be weighed
5 mg/mL
100 mL
500 mg = 0.5 g
concentration desired X volume desired = mass of solute to be weighed
Measuring for % Mass/Volume Solutions
To make 100 mL of a 3% CuSO4 solution
3 % = 0.03
__________
____________
conc desired (decimal)
0.03 g/mL
conc desired
X
volume desired
100 mL
X
volume desired
____________g_____
=
mass of solute needed
3 g CuSO4
= mass of solute needed
Measuring for Molar Solutions
To make 300 mL of a 0.5M NaOH solution.
Convert 300 mL = 0.3 L
_________
concentration
____________
X
__________
_________g__
volume desired X molecular weight = mass of solute
desired (mol/L)
(L)
(g/mol)
(g)
Molecular Weight ?
Moles are used to count molecules and atoms since they are too small to
count individually. 1 mole equals the amount of molecules that gives a
mass, in grams, equal to that substance’s molecular or formula weight.
The formula weight (FW or MW) can be determined using a periodic table
or by looking at a chemical reagent bottle.
For Molar Solutions you need the MW
Determine the molecular weight of the solute
The formula weight can be determined using a periodic table or by looking
at a chemical reagent bottle
Measuring for Molar Solutions
To make 300 mL of a 0.5M NaOH solution.
Convert 300 mL = 0.3 L
0.5 mol/L
concentration
desired (mol/L)
0.3 L
X
40 g/mol
6g
volume desired X molecular weight = mass of solute
(L)
(g/mol)
(g)
6 g of NaOH is measured on a balance and put into an appropriate vessel.
Then, solvent is added up to the 300 mL graduation.
4. Mixing the Solute and Solvent
Mass/Volume solutions
100 mL of a 5 mg/mL hemoglobin solution.
5 mg/mL
100 mL
500 mg = 0.5 g
concentration desired X volume desired = mass of solute to be weighed
250 mL beaker
100 mL
solvent (dH20 or buffer)
0.5 g hemoglobin
PPT Demos on the Encore® CD
25 tutorials for the basic SLOP (standard lab operating procedures) skills
Step 5 Checking the Solution Preparation
I like to teach solution prep using copper sulfate since it is blue
and can be visualized (relative number of molecules compared)
in the Spec 20D+ at 600 nm)
I also check the volume and labels on all tubes.
Other methods of checking solution prep?
Now YOU try it.
Make the following solutions but before you do:
• Do all the calculations showing the equations with all the units of measurement shown.
• Diagram how you are going to prepare the solution.
• After you prepare the solution, check it in the spec. Demonstrate how to take up and dispense a sample .
Make all the solutions in 15 mL tubes and then transfer 3 mL into 13x100 mm tubes for checking in
the spec.
• 4 mL of 0.5 M cupric sulfate pentahydrate
• 5 mL of 250 mM cupric sulfate pentahydrate
• 6 mL 125 mM cupric sulfate pentahydrate
Note:
M
1000
mM
Check each solution in the spec at 600 nm by measuring the absorbance.
Use 3 mL of the solution to be checked, in a 13x100 mm cuvette.