Dillutions and Sollutions
Dillutions:
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What is a dilution?
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A dilution is when one substance (often, but not always, water) is added to another to reduce the concentration of the first substance. The original
substance being diluted may be called the Stock Solution, whereas the diluting substance is called the Diluent.
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For example, a 1 in 10 dilution is accomplished by adding 1 ml of stock solution to 9 ml of diluting solution.
dilution and proportions: The concepts of dilutions and proportions are related.
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A dilution can be written as a ratio, 1 ml/10 ml (1 in 10 dilution).
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A 1 in 10 dilution can be accomplished in a number of ways and are proportional:
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1 ml/10 ml = 10ml/90 ml.
Dilution terminology:
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1 part of a stock solution diluted by 9 parts of diluent is 1 part in 10 ml total volume or a 1/10 dilution.
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An undiluted substance, by definition is called 1/1.
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When talking about dilutions, the symbol : means parts.
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1 ml of stock in 10 ml diluent is written as 1:9 (1 part stock in 9 parts diluent).
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Additional examples…
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1:2 means 1 part stock in 2 parts diluent (3 parts total)
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1/2 means there are 2 parts total volume (1 part stock in 1 part diluent).
Many dilutions will involve concentrations, so remember to keep track of your concentrations when performing these types of dilutions.
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For example, a stock has a concentration of 20. mg (milligrams = 1/1,000 of a gram), a dilution is made by removing 1 ml stock and placing it in 14
ml of water. The dilution is 1:14 or 1/15. What is the concentration of the diluted solution?
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X = 1.3 mg/L
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The concentration of a solution was determined by multiplying the concentration of the original solution times the dilution
(expressed as a fraction).
Dilution equation: (initial concentration)(initial volume) = (final concentration)(final volume) if you know 3 of the values, you can solve for the 4th value
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You have a “stock solution” of 0.50M NaCl, you want to make 100ml of 0.10M NaCl. How much of the initial “stock solution” do you need?
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C1= 0.50M NaCl…….initial concentration of stock solution
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V1=?.........................initial volume of stock solution used
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C2 = 0.10M NaCl…...Final concentration that needs to be produced
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V2 = 100.0 ml……….Final volume of the diluted solution produced
(C1)(V1) = (C2)(V2) 
1.
2.
3.
=
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0.50MNaCl
1
0.50MNaCl
=
0.10MNaCl 100.0ml
=20.ml of stock 0.50 M NaCl is needed
0.50MNaCl
In a clean 100 ml graduated cylinder, measure out exactly 20.0 ml of 0.50 M NaCl
Q.S to the 100 ml mark using dH2O
Transfer into a clean reagent bottle, and label and store
Problems:
1.
You have 50.0ml of 50X TAE
a. You are doing Gel electrophoresis experiment set at 100V. This requires 1X TAE, if you do a dilution, how much 1X
TAE can you make?
b. Your lab partner is doing a Gel electrophoresis experiment set at 200V. You need to make 1500. ml of 0.25X TAE to run
the experiment. How would your lab partner make the solution?
2. If you prepare a 1/10 dilution of a 10. mg/mL solution, what is the final concentration of the solution?
Challenge Question: Suppose you have 20 μL of a very expensive enzyme and you cannot afford to purchase more. Its concentration
is
. You are performing an experiment that requires tubes with a concentration of
and each tube will
have 5 mL total volume. How much does each tube require? How many tubes can you prepare before you run out of enzyme?
Solutions: Solutions always involve concentrations although such ratios are not readily evident in some cases. Recipes for solutions can
express concentrations in a number of ways, for example…
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Weight per volume is the simplest manner of expressing a concentration.
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1.
2.
3.
4.
5.
Molarity is the number of moles of a substance dissolved in 1 L of solution or (
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For example,
).
Of course, a mole of any element contains 6.02 x 1023 atoms (Avagadro’s number). The weight of a mole of a given element is equal to its atomic weight
in grams, or its gram atomic weight (more properly given as mass).
Compounds are composed of atoms of two or more different elements bonded together. The gram formula weight (FW) or gram molecular weight (MW)
of a compound is the weight in grams of 1 mole of the compound (
)
Percent is always expressed with the numerator representing the amount of solute and the denominator is 100 units of total solution. There are generally two
ways in which percentages are expressed.
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Weight per volume (w/v) is the weight of the solute (in grams) in 100 mL of solution. For example, 20 g of NaCl in 100 mL of total solution is a 20% (w/v)
solution.
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Volume percent (v/v) is when both the amount of solute and total solution are expressed in volumes. For example, 10 mL of ethanol in a total solution of
100 mL is a 10% solution.
Short hand description of how to prepare a particular solution starting from powder. Ex: if you were making 100 ml of 8% (m/v) NaCl
6.
Weigh out 8.00g of NaCL in a weigh boat
Add approximately half of the final volume (50ml) of distilled water into a clean 100.0ml graduated cylinder.
Use a powder funnel to add the 8.00 g of NaCl into the graduated cylinder.
Using distilled water, rinse all remaining NaCl off the weigh boat and powder funnel into the graduated cylinder.
Dissolve the powder NaCl
Using distilled H2O, Q.S.* to 100 ml *Q.S. is a short hand biotech term that means add solvent (in this case water) to get the meniscus just to the line…To do this make sure you switch for distilled water squirt bottle to distilled water dropper, 7.
8.
Transfer the 8% NaCl into a clean Reagent bottle
Label and store
because if you go over by just a drop, you have to throw out the solution and start again!
problems: 1. How much proteinase K is needed to make up 250 μL of a 10 mg/mL solution?
2. How much solute is required to make 250 mL of a 1 M (molar) solution of KCl (FW =
3. How would you prepare 600.0 mL of a 0.4 M solution of Tris buffer (FW =
5. How would you prepare a 35 mL of a 95% (v/v) solution of ethanol?
6. How would you prepare 600.0 mL of a 15% (w/v) solution of NaCl? .
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