Transcript Solution Prep Review & Practice Problems

Solution Concentration
“Which Formula
Should I Use?”
Solution Concentrations
Used in Lab
• Explicit: g/L or mg/ml
• Percent: %
• Molar: M, mM or µM
Explicit Concentration
Expressed as a specific mass
per specific volume
Mass may be g, mg, µg, etc
Volume may be to be L, ml, µl, etc
Examples: X g OR X mg OR Xµg OR Xµg
L
ml
µl
ml
Explicit Concentration Tips
• Formula weight does not matter!
• Set up as a fraction
• Convert units as needed to make unit prefixes the
same in the numerator and denominator
• Simplify the fraction until the denominator is equal to 1
• Used to re-hydrate lyophilized reagents and make
media
Percent Solution
X% (w/v) solution = X grams solute
100 ml solution
OR
X% (v/v) solution = X ml solute
100 ml solution
Percent Solution Tips
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Formula weight does not matter!
Solid solute indicates w/v
Liquid solute indicates v/v
Gel concentrations expressed this way
Look for ”%”
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 solution
expressed in liters
Molar Solutions Tips
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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 “µM”
Diluting Solutions
Sometimes you need to dilute a stock
solution in order to make a working
solution…
Diluting Concentrated
Solutions
CsVs = CwVw
Cs = concentration of stock solution
Vs = volume of stock solution needed
Cw = desired concentration of working solution
Vw = desired volume of working solution
Diluting Solutions Tips
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Stock buffers diluted this way
Solute is liquid
Volume usually expressed in ml
Usually solving for “Vs”
• Look for “X”
Practice!
Now that you know how to use the formulas,
you can practice knowing which formula to
use.
Continue for practice problems in making
solutions in the lab. Read each problem,
select which formula you need to apply, and
see if you can solve the problem.
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.
Practice #1
You need to make 1L
of LB/Amp media.
The concentration of
Amp in the media
should be 0.1 mg/ml.
How much Amp
powder do you need
to weight out?
choose formula:
g = M •FW • L
CsVs = CwVw
X grams solute
100 ml solution
mg/ml
Practice #2
We purchase PBS
as a 20X stock
solution. How would
you make 150 ml of
1X PBS?
choose formula:
g = M •FW • L
CsVs = CwVw
X grams solute
100 ml solution
mg/ml
Practice #3
Binding Buffer is 4M
Ammonium Sulfate
[(NH4)2SO4].
How would you make
300 ml of
this solution?
choose formula:
g = M •FW • L
CsVs = CwVw
X grams solute
100 ml solution
mg/ml
Practice #4
A 30 mg vial of
Ampicillin is
rehydrated with
3 ml of sterile distilled
water. What is the
concentration of
ampicillin in this
solution?
choose formula:
g = M •FW • L
CsVs = CwVw
X grams solute
100 ml solution
mg/ml
Practice #5
Methylene Blue is
used to stain DNA.
How would you make
250 ml of a 0.5%
solution of Methylene
Blue using powdered
Methylene Blue?
choose formula:
g = M •FW • L
CsVs = CwVw
X grams solute
100 ml solution
mg/ml
Practice #6
Your protocol calls
for a 30 ml, 0.8%
DNA gel. How much
agarose powder do
you need?
choose formula:
g = M •FW • L
CsVs = CwVw
X grams solute
100 ml solution
mg/ml
Practice #7
You need 10 mM
EDTA solution to
dilute your DNA.
How would you make
50 ml of
10 mM EDTA?
choose formula:
g = M •FW • L
CsVs = CwVw
X grams solute
100 ml solution
mg/ml
Practice #8
We have 50X TAE.
You need 1X TAE to
run your gel. How
would you make 400
ml of 1X TAE?
choose formula:
g = M •FW • L
CsVs = CwVw
X grams solute
100 ml solution
mg/ml
Practice #9
How would you
prepare 250ml of a
40mM solution of
Magnesium Chloride
[MgCl2•6H2O]?
choose formula:
g = M •FW • L
CsVs= CwVw
X grams solute
100 ml solution
mg/ml
Practice #10
We have 2M glucose
solution. How would
you make 100 ml of
2mM glucose
solution?
choose formula:
g = M •FW • L
CsVs= CwVw
X grams solute
100 ml solution
mg/ml
CONGRATULATIONS!
By carefully reading
the problems and
picking out the
unknown, you were
able apply the correct
formula and do the
math!