EXPRESSING CONCENTRATIONS OF SOLUTIONS:                   

 

I.                 Unsaturated, Saturated, and Supersaturated Solutions

 

A.     An unsaturated solution is one that is not holding all of the solute that it can hold at that temperature.

B.     A saturated solution is one that is holding the maximum amount of solute it can hold at that temperature.

C.     A supersaturated solution is one that is holding more than the maximum amount that it is usually capable of holding at that temperature.

 

Q.     How can you tell the difference between the types of solutions listed above?

R.      

A.         The answer is very simple.  Drop of crystal of solute into the solution and observe what happens:  (1) if the      crystal dissolves, the original solution was unsaturated; (2) if the crystal does not dissolve, but settles to the bottom and remains there, the original solution was saturated; (3) if the addition of a single crystal of solute causes many other crystal to appear and settle to the bottom, then the original solution was supersaturated.

 

II.                

III.                         Percent refers to the parts per 100 parts, and the formula Percents is as follows:

IV.                         (also see Handout under Percent Concentration)

 

          % = Part    X  100

                 Whole

 

A.     Percent by Mass/Mass or %(m/m)

 

% by m/m is simply the mass of the solute per 100 g of solution.

 

Example:  In order to prepare a 5.0% (m/m) solution of glucose (C6H12O6) weigh out 5.0 g of glucose and add water until the total weight of the solution is 100. grams.

 

     % = 5.0 g glucose     X 100 =  5.0 % (m/m) solution

             100. g solution

         

B.     Percent by Mass/Volume or % (m/v)

 

% by m/v is the mass of the solute per 100. Ml of the solution.

Example:  In order to prepare a 5.0% (m/v) solution of glucose (C6H12O6) solution, weigh out 5.0 grams of glucose.  Dissolve this in water and add water to the 100. ml mark.  

 

II.               Percent Composition (continued)

 

     % = 5.0 g glucose      X 100 = 5.0% (m/v) solution

            100. g solution

 

C.     Percent by Volume-Volume or % (v/v)

 

% by v/v is the volume of the solute per 100 ml of the solution.

 

Example:  In order to prepare a 5.0% (v/v) solution of alcohol, measure out 5.0 ml of  the alcohol and add water to the 100.ml mark.

 

% = 5.0 ml of alcohol  X 100 = 5.0 % (v/v) solution

       100. ml solution

 

Sample Problems:

 

1.     Find the mass of NaCl contained in 65 g of a 3.5% (m/m) solution.

 

 

 

 

2.     Find the mass of glucose, C6H12O6 contained in 35 ml of a 4.2% (m/v) solution.

 

 

 

 

3.     Find the volume of methanol contained in 250. Ml of a 1.5 % (v/v) solution.

 

 

 

 

 

Check your set-ups and answers:

 

 

 


 

 

 

 

 

 

2.     Find the volume of methanol contained in 250. ml of a 1.5 % (v/v) solution.

 

1.5% (250.ml) = 3.75 ml methanol = 3.8 ml methanol