The 55 Limit-A Useful Rule of Thumb Although the federal government may have revoked the 55-mph limit for rural highways, 55 is stillan important limit

for chemists. Chemistry students occasionally calculate the concentration of solutions to he in the hundreds and thousands of moles per liter. Generally, such answers are incorrect. There are about 55 moles ofwater in a liter of pure water. It would be difficult to get more material into water than there can he water in water. It is, therefore, auseful rule of thumb for stu- dents that (at a pressure of 1 atm and temperature of 298 K) calculated concentrations higher than 55 m o l L should he regarded with extreme suspicion.

Benjamin P. Ruekberg Kansas Newman College

3100 McCormick Wichita. KS 67213

892 Journal of Chemical Education