MHS Chemistry
Colligative Properties
This is only a very rough page to include the basics of the basics.
| Molality = | moles of impurities |
| kilograms of solvent |
Molality will be symbolized on this page by m. Note that it is different from concentration, which is moles of solute (regardless of dissociation) per liter of solution. If the solvent dissociates (breaks into ions) you must remember to account for each ion: one mole of table salt, NaCl, produces TWO moles of impurities.
The boiling point of a solution elevates (increases) when there are impurities, and the freezing/melting point depresses (lowers) when there are impurities. The formula is for both changes is
DT = km
It's up to you to remember whether the change is an elevation or depression. Below is a table of freezing point and boiling point constants for several chemicals. The label on the constants (k) is C/m.
| NAME | Formula | MW |
FP (C) |
k(f) |
BP (C) |
K(b) |
| 1,2-Ethanediol | C2H6O2 | 62.07 |
-13 |
3.11 |
197.3 |
2.26 |
| 1,4-Dioxane | C4H8O2 | 88.11 |
11.8 |
4.63 |
101.5 |
3.270 |
| 2-Butanol, 2-methyl- | C5H12O | 88.15 |
-8.81 |
10.4 |
102.4 |
2.255 |
| Acetamide, N,N-dimethyl- | C4H9NO | 87.12 |
-20 |
4.46 |
165 |
3.22 |
| Acetic acid | C2H4O2 | 60.05 |
16.6 |
3.63 |
117.9 |
3.22 |
| Acetone | C3H6O | 58.08 |
-94.81 |
2.40 |
56 |
1.80 |
| analine | C6H7N | 93.13 |
-6 |
5.50 |
184.1 |
3.82 |
| Benzene | C6H6 | 78.11 |
5.5 |
5.07 |
80.15 |
2.53 |
| Benzonitrile | C7H5N | 103.12 |
-12.7 |
5.35 |
191.1 |
2.53 |
| Camphor | C10H16O | 152.24 |
178.8 |
38.8 |
207.4 |
5.61 |
| Carbon disulfide | CS2 | 76.14 |
-111.5 |
3.83 |
46.13 |
2.34 |
| Carbon tetrachloride | CCl4 | 153.82 |
-23 |
29.8 |
76.5 |
5.03 |
| Chloroform | CHCl3 | 119.38 |
-63.6 |
4.68 |
60.19 |
3.63 |
| Cyclohexane | C6H12 | 84.16 |
6.59 |
20.8 |
80.88 |
2.79 |
| Cyclohexane, methyl- | C7H14 | 98.19 |
-126.6 |
14.3 |
100.9 |
2.6 |
| Cyclohexanol | C6H12O | 100.16 |
6.53 |
40.8 |
160.8 |
3.5 |
| diphenyl | C12H10 | 154.21 |
69 |
8.0 |
256.1 |
7.08 |
| DMSO | C2H6OS | 78.14 |
18.5 |
3.96 |
189 |
3.22 |
| Ethane, 1,2-dibromo- | C2H4Br2 | 187.86 |
9.89 |
12.5 |
131.6 |
6.608 |
| Ether, diethyl | C4H10O | 74.12 |
-116.31 |
1.79 |
34.42 |
2.02 |
| Formic acid | CH2O2 | 46.03 |
8.3 |
2.38 |
101 |
2.4 |
| glycerol | C3H8O3 | 92.09 |
18.2 |
3.56 |
290 |
6.52 |
| Naphthalene | C10H8 | 128.17 |
80.19 |
6.94 |
217.9 |
5.80 |
| nitrobenzene | C6H5NO2 | 123.11 |
5.69 |
6.87 |
210.85 |
5.24 |
| phenetole | C8H10O | 122.17 |
-29.5 |
7.15 |
169.8 |
5.0 |
| Phenol | C6H6O | 94.11 |
40.9 |
7.27 |
181.5 |
3.51 |
| Pyridine | C5H5N | 79.1 |
-41.6 |
4.26 |
115.2 |
2.710 |
| Quinoline | C9H7N | 129.16 |
-14.78 |
1.95 |
237.1 |
6.30 |
| toluene | C7H8 | 92.14 |
-94.91 |
3.55 |
110.6 |
3.33 |
| Water | H2O | 18.01 |
0 |
1.86 |
100 |
0.513 |
This property can be used to determine molecular weight. Measuring the change in freezing or boiling point for a known mass of material in any of the solvents above will allow you to determine the number of moles; molecular weight is just mass/moles.