Lab One: SOLUTION MAKING!

I know what you thought when you started this lab. "Is this a joke? How dumb! I know how to dilute something, and why the hell are we making solutions the first day of lab? We are supposed to get out EARLY!!!"

Well I hope you didn't slack on those calculations because all those solutions will be used later this semester....in YOUR experiments!!!

So let's talk about dilution calculations...

Harder than it seems, right? But I'm going to break it down.

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Volume to Volume Dilutions

This type of dilutions describes the ratio of the solute to the final volume of the diluted solution.

For example, to make a 1:10 dilution of a 1M NaCl solution, you would mix one "part" of the 1M solution with nine "parts" of solvent (probably water), for a total of ten "parts." Therefore, 1:10 dilution means 1 part + 9 parts of water (or other diluent).



For example: if you needed 10 mL of the 1:10 dilution, then you would mix 1mL of the 1M NaCl with 9mL of water.

Or: if you needed 100mL of the 1:10 dilution, then you would mix 10mL of the 1M NaCl with 90mL of water.

The final concentration of NaCl in both cases is 0.1M.

C1V1=C2V2

The Big Boy of Dilutions...know this!!!

Sometimes it is necessary to use one solution to make a specific amount of a more dilute solution. To do this, you can use the formula:

V1C1 = V2C2

where:
V1 = volume of starting solution needed to make the new solution
C1 = concentration of starting solution
V2 = final volume of new solution
C2 = final concentration of new solution

For example: Make 5mL of a 0.25M solution from 2.5mL of a 1M solution.

V1C1 = V2C2
(V1)(1M) = (5mL)(0.25M)
V1 = [(5mL)(0.25M)] / (1M)
V1 = 1.25mL

So you will need to use 1.25mL of the 1M solution. Since you want the diluted solution to have a final volume of 5mL, you will need to add ( V1-V2 = 5mL - 1.25mL) 3.75mL of diluent.

Serial Dilutions

Sometimes it is necessary to dilute by a large factor so several serial dilutions are necessary.
To make a 1:10 dilution a 1:100 via serial dilution...

Take 1 part diluted to 9 parts water! This is another 1:10 dilution!

1:10 x 1:10= 1:100

Solutions made using Percentage by weight (w/v)

The number of grams in 100mL of solution is indicated by the percentage.
For example, a 1% solution has one gram of solid dissolved in 100mL of solvent. To make this type of solution properly, you should weight 1g and dissolve it in slightly less than 100mL. Once the solids have dissolved, you can bring the volume up to the final 100mL

Solutions made using Percentage by Volume (v/v)

In this case, the percentage indicates the volume of the full strength solution in 100mL of dilute solution.

To make a 60% Ethanol solution:

Step 1: Measure 60mL ethanol

Step 2: Add 40mL water to bring to 100mL

Molar Solutions

A 1 molar solution is a solution in which 1 mole of a compound is dissolved in a total volume of 1 litre.

For example:
The molecular weight of sodium chloride (NaCl) is 58.44, so one gram molecular weight (= 1 mole) is 58.44g. If you dissolve 58.44g of NaCl in a final volume of 1 litre, you have made a 1M NaCl solution.

To make a 0.1M NaCl solution, you could weigh 5.844g of NaCl and dissolve it in 1 litre of water; OR 0.5844g of NaCl in 100mL of water (see animation below); OR make a 1:10 dilution of a 1M sample.

Do it on your own:

How would you make a 500mL dilution of a 0.05M NaCl solution?

Answer will be posted when someone figures it out! Post your answers in the comment section!

Courtesy of http://www.wellesley.edu/Biology/Concepts/Html/volumetovolume.html