Then convert mL to liters:
Then divide:
Dilution
Dilution is the process of taking a more concentrated solution and adding water to make it less concentrated. The more concentrated solution before the dilution is performed is known as the stock solution. You can relate the concentration of the stock solution to the concentration of the diluted solution using the equation below:
M1V1 = M2V2
where M is molarity and V is the volume, in liters, of the solution. Try the following example using this equation.
Example
What volume of 6.0 M sulfuric acid (H2SO4) must be used to prepare 2.0 L of a 0.10 M H2SO4 solution?
Explanation
Just plug the numbers into the formula! Be careful to read closely.
M1V1 = M2V2
(6.0 M) (V1) = (0.10 M) (2.0 L)
V1 = 0.033 L
or 33 mL should be measured out and then diluted by adding enough water to make 2.00 L total volume.
Mass Percent (Weight Percent)
The mass percent of a solution is another way of expressing its concentration. Mass percent is found by dividing the mass of the solute by the mass of the solution and multiplying by 100; so a solution of NaOH that is 28% NaOH by mass contains 28 g of NaOH for each 100 g of solution. Here’s the equation:
Now try a problem involving the equation:
Example
A solution is prepared by mixing 5.00 g ethanol (C2H5OH) with 100.0 g water. Calculate the mass percent of ethanol in this solution.
Explanation
Plugging the values we were given into the mass percent equation, we get:
Molality (m)
The molality of a solution is a measure of the number of moles of solute per kilogram of solvent. Whereas the molarity of a solution is dependent on the volume of the solution, the molality is dependent on the mass of the solvent in the solution. Do not get these confused, and when you see either term on the SAT II Chemistry test, double-check to make sure which one they’re talking about—the words look similar, too! Try an example:
Example
A solution is prepared by mixing 80.0 g of sodium hydroxide (NaOH) with 500.0 g of water. Calculate the molality of this solution.
Explanation
Convert grams of solute to moles:
Convert grams of solvent to kg:
Divide:
Electrolytes
Certain solutions are capable of conducting an electric current and these solutions are referred to as electrolytes. Generally speaking, we say that there are three classes of electrolytes (solutions that conduct a current): acids, bases, and salts.
