Problems with solution making
In order to perform a successful experiment most of the time one has to begin with preparing solutions required for it.When you begin you realize all solutions are required in mM which might be confusing in the beginning but its very important to get it correct or else be prepared for some strange results.Here some simple ways for preparing mM solutions and diluting solutions from more concentrated solutions.
Solutions and Dilutions
equivalent weight = the formula weight of the solute) per L of solution.In most cases, a 1 M solution will be too concentrated, so concentrations are usually given as mM (=0.001 M).
How to make a 1 M solution?
a) Add up the atomic weights of the elements that comprise the compound of interest, including added water, or find the formula weight directly (it is often listed on the label). Weight out this amount of the solute, and dissolve in less than 1 liter of water. After the solute is completely dissolved, add water up to the 1 L level.
3. How to make other concentrations?
Figure out how much solute you would need for one Liter of a 1 M solution and use ratios to arrive at the correct figure.
Example: to make 50 mls of a 10 mM sucrose solution I would first figure out how to make a liter of 1.0 M sucrose (sucrose FW = 380; therefore you would add 380 g sucrose per liter of solution. Next, I set up a ratio to determine how much sucrose I would need to make a Liter of the solution at the named concentration. Because you only need a 10 mM solution you would only have to add 10mM/1,000 mM as much sucrose or .010 (380g) or 3.8 grams. Lastly, I calculate the amount of sucrose needed for
the volume I have to make up, in this case 50 mls. Therefore, I only need 50mls/1000mls X 3.8g = 0.19g. So to make up the solution you would add 0.19g sucrose to about 40 mls water, dissolve the sucrose, and add water up to 50 mls.
Concentration Dilutions
To produce a given amount of a less concentrated solution from a more concentrated stock solution the following formula is
used:
C1V1 = C2V2
C1 = original concentration (con. of stock solution)
C2 = final concentration
V1 = original volume (amount to be taken from stock solution)
V2 = final volume (the amount of dilute solution you want to make)
Example: To make 100ml of a 0.05 M solution of NaCl (also referred to as a 50 mM solution) from a 1 M stock solution.
1 M • ? mL = 0.05 M • 100 mL
mL = 5 M • mL
1 M
mL = 5
The original volume (V1) is almost always the quantity you are looking for since you usually know the stock concentration and the amount and concentration you want to achieve (if the final volume is not given, you can figure it out based on how much you are likely to need for the job at hand). What you are usually looking for is how much of the stock to use (V1). It is not necessary for the volume to be measured in Liters in this formula as it is in making molar solutions; however, the units for V1 and V2 must be the same.
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