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Solution Concentration
Which Formula
Should I Use?
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Solution Concentrations
Used in Lab
Mass/Volume: g/L or mg/ml
Percent: %
Molar: M, mM or M
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Mass/Volume Concentration
Expressed as a specific mass
per specific volume
Mass may be g, mg, g, etc
Volume may be to be L, ml, l, etc
xamples X g OR X mg OR Xg OR Xg
L ml l ml
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Mass/Volume Concentration
Tips
Formula weight does not matter!
Set up as a fraction Simplify the fraction until the denominator is
equal to 1
Used to re-hydrate packaged vials and makemedia
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Percent Solutions
X% (w/v) solution = X grams solute
100 ml solution
OR
X% (v/v) solution = X ml solute
100 ml solution
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Percent Solutions Tips
Formula weight does not matter!
Solidsolute indicates w/v Liquidsolute indicates v/v
Gel concentrations expressed this way
Look for %
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Molar Solutions
g = M FW L
g =grams of solute to be weighed out
M = molarity of the desired solution
FW = formula weight of the solute
L= volume of desired solutionexpressed in liters
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Molar Solutions Tips
Formula weight does matter
Solute is dry
Volume must be expressed in liters Usually solving for g
Add any water(s) of hydration to the FW of the
solute
Look for M or mM or M
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Sometimes you need to dilute a stock
solution in order to make a working
solution
Diluting Solutions
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Diluting Concentrated
Solutions
C1V1= C2V2
C1= concentration of stock solution
V1= volume of stock solution needed
C2= desired concentration of working solution
V2= desired volume of working solution
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Diluting Solutions Tips
Stock buffers diluted this way
Solute is liquid Volume usually expressed in ml
Usually solving for V1
Look for X
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Now that you know how to use the formulas,
lets practice knowing which formula to use.
The following slides will give you practice
problems for making solutions in the lab. Read
each problem, select which formula you needto apply, and see if you can solve the problem.
Practice!
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Directions
Each practice problem will give you four
formula choices. Choose the formula that
applies to the problem. Then solve the
problem yourself.
On each CORRECT!! slide, click to see the
problem set-up, then click again for the
solution so you can check your answer.
Then click the blue button to go to the next
problem.
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Practice #1
You need to make 1L
of LB/Amp media.
The concentration ofAmp in the media
should be 0.1 mg/ml.
How much Amp
powder do you needto weight out?
g = M FW L
C1V1= C2V2
X grams solute
100 ml solution
mass/volume
choose formula:
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Practice #2
We purchase PBS
as a 20X stock
solution. How wouldyou make 150 ml of
1X PBS?
g = M FW L
C1V1 = C2V2
X grams solute
100 ml solution
mass/volume
choose formula:
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Practice #3
Binding Buffer is 4M
Ammonium Sulfate
[(NH4)2SO4].How would you make
300 ml of
this solution?
g = M FW L
C1V
1= C
2V
2
X grams solute
100 ml solution
mass/volume
choose formula:
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Practice #4
A 30 mg vial ofAmpicillin isrehydrated with
3 ml of sterile distilledwater. What is theconcentration of
ampicillin in thissolution?
g = M FW L
C1V
1= C
2V
2
X grams solute
100 ml solution
mass/volume
choose formula:
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Practice #5
Methylene Blue is
used to stain DNA.
How would you make250 ml of a 0.5%
solution of Methylene
Blue using powdered
Methylene Blue?
g = M FW L
C1V
1= C
2V
2
X grams solute
100 ml solution
mass/volume
choose formula:
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Practice #6
Your protocol calls
for a 30 ml, 0.8%
DNA gel. How muchagarose powder do
you need?
g = M FW L
C1V
1= C
2V
2
X grams solute
100 ml solution
mass/volume
choose formula:
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Practice #7
You need 10 mM
EDTA solution to
dilute your DNA.How would you make
50 ml of
10 mM EDTA?
g = M FW L
C1V1= C2V2
X grams solute
100 ml solution
mass/volume
choose formula:
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Practice #8
We have 50X TAE.
You need 1X TAE to
run your gel. Howwould you make 400
ml of 1X TAE?
g = M FW L
C1V1= C2V2
X grams solute
100 ml solution
mass/volume
choose formula:
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Practice #9
How would you
prepare 250ml of a
40mM solution ofMagnesium Chloride
[MgCl26H2O]?
g = M FW L
C1V1= C2V2
X grams solute
100 ml solution
mass/volume
choose formula:
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Practice #10
We have 2M glucose
solution. How would
you make 100 ml of2mM glucose
solution?
g = M FW L
C1V1= C2V2
X grams solute
100 ml solution
mass/volume
choose formula:
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CONGRATULATIONS!
By carefully reading
the problems and
picking out theunknown, you were
able apply the correct
formula and do the
math!