AP Chemistry - Molality, Mole Fraction and Mole Percent Worksheet
1.    
Water freezes at a lower temperature when it contains solutes.  To study the effect of methyl alcohol on the freezing point of water, you decide to begin by preparing a series of solutions of known molalities.  Calculate the number of grams of methyl alcohol (CH3OH) needed to prepare a 0.250 m solution, using 2000 g of water.

2.
If you prepare a solution by dissolving 4.00 g of NaOH in 250 g of water, what is the molality of the solution?

3.
A solution of methyl alcohol, CH3OH, in water has a concentration of 1.5 m.  Calculate the following:

a)   The mole fractions of methyl alcohol and water.
b)    The w/w percent of methyl alcohol

4.
An aqueous solution of Na2SO4 has a concentration of 0.370 m.   Its density is 1.0436 g/mL.  Calculate the following:

a)    The mole fractions of Na2SO4 and H2O.
b)    The w/w percent concentration of Na2SO4.
c)     The molar concentration of Na2SO4.

5.
In an aqueous solution of sulfuric acid, the concentration is 2.40 mole percent of acid.  The density of the solution is 1.079 g/mL.  Calculate the following:

a)   The molal concentration of H2SO4.
b)   The w/w percent of the acid.
c)   The molarity of the solution.
 
6.
In an aqueous solution of KNO3, (formula weight 101.1)  the concentration is 3.28 mole percent of the salt.  The density of the solution is 1.1039 g/mL.  Calculate the following:

a)   The molal concentration of KNO3.
b)   The w/w percent of KNO3.
c)    The molarity of the solution.

7.
A solution of NaCl in water has a concentration of 22.0% w/w.  Calculate the following:

a)  The molality of this solution.
b)  The mole fractions of NaCl and water.

8.
A solution of HNO3 in water has a concentration of 10.00% w/w. Its density is 1.0543 g/mL.  Calculate the following:

a)   The molality of this solution.
b)   The mole percent of HNO3.
c)    The molarity of the HNO3.

9.
A solution of sodium nitrate has a concentration of 0.733 M.  Its density is 1.0392 g/mL.  Calculate the following:

a)   The molality of the solution.
b)   The mole percent of NaNO3 in the solution.
c)    The w/w concentration of NaNO3.

10.
A solution of hydrochloric acid has a concentration of 0.275 M and a density of 1.0031 g/mL.  Calculate the following:

a)   The molality of the solution? (how does it compare numerically with the given molarity?)
b)   The w/w concentration of HCl.
c)    The mole percent of HCl in the solution.

11.
A solution of ethyl alcohol, C2H5OH, in water has a concentration of 6.211 mol/L.   At 20oC, its density is 0.9539 g/mL.  Calculate the following.

a)   The molality of the solution.
b)   The w/w concentration of the alcohol.
c)   The mole percent of the alcohol.
d)   The density of ethyl alcohol is 0.7893 g/mL and the density of water is 0.99823 g/mL at 20oC.  Calculate the v/v concentration of ethyl alcohol in this solution.

12.
A solution of NH3 in water is at a  concentration of 1.00% w/w. Its density is 0.9938 g/mL.  Calculate the following.

a)  The molarity of the solution.
b)  The molality of the solution.
c)  The mole percent of NH3.

13.
A solution is prepared by mixing equal weights of water (H2O) and glycerol (C3H8O3).  At 20oC this solution has a density of 1.126 g/cm3.   What is the mole fraction and the molarity of glycerol  in this solution?   If water is considered to be the solvent, what is the molality of glycerol?

14.
A  solution is prepared by mixing 10.0g portions of water (H2O), methyl alcohol (CH3OH), and acetone [(CH3)2CO].  What is the mole fraction of each of these components?

15.
A solution containing sucrose (C12H22O11), 93.0 g/L, has a density of 1.034 g/mL at 22oC.  What is the molarity and the molality of sucrose in this solution?

16.
An aqueous solution of acetone [(CH3)2CO], which is 8.50% w/w acetone has a density of 0.9867 g/mL at 20.0oC.  What are the mole fraction, the molality, and the molarity of acetone in this solution?  (acetone does not dissociate in aqueous solution.)

17.
An aqueous solution of ethanol (C2H5OH) was prepared by adding 69.00 grams of pure ethanol to a 1 L volumetric flask and diluting to the mark.   The resulting solution had a density of 0.9862 g/mL.  What are the mole fraction, the molality, and the molarity of this solution?

18.
The principal solute in vinegar is acetic acid (CH3COOH).  If a sample of vinegar has a 5.5% w/w acetic acid and a density of 1.006 g/mL, what is the molarity of acetic acid?

19.
Values of the weight percentage of the acid and the density (at 20oC) of concentrated aqueous solutions of reagent grade acids commonly provided by chemical manufacturers are:

HCl             36.0% w/w     D = 1.19 g/cm3  
HNO3         69.5% w/w     D = 1.42 g/cm3  
H2SO4        96.0% w/w     D = 1.84 g/cm3  

Calculate the molarity and molality of acid in each of these solutions.