JOHN J. ALEXANDER University of Cincinnati Cincinnati. OH 45221
Empirica! Formulas-A
Ratio Problem
Kerro Knox
Cleveland State University Cleveland, OH 44115 Atoms are too small to see, hut young men (boys, B) and young women (girls, G) are highly visible, especially to each other. The problem of determining the empirical formula of a chemical compound from its composition by weight percent and from the atomic weights of its constituent elements can he made meaningful (i.e., related to sex) by solving an analogous problem using everyday objects (i.e., boys and girls). The latter problem is suitable a t the most elementary level; it involves the same reasoning as the former. Question
Freshman boys (B) on the average weigh 160 lh and freshman girls (G) 120 lh. A freshman chemistry class consists of 66.7%by weight of R and 33.3%G. What is the numerical ratio of boys to girls in the class? What is the formula of the class expressed as B,G,, where n and m are small whole numbers (no fractional students, please)? Acceptable Solution
Working to the three significant figures given in the data and carrying along units, one calculates: 'B1lOOib' class = 0.417 B1100 lb class Ifill lb BIB G1lOOlb class = 0.278 GI100 lb class "" .,~
'
,.
7 ,,
0.417 BI10l -class - 1.50 BIG 0.278 C . .uv ~ ~ c l a s s The decimal 1.50 is recoenized as the fractional 1'17. of which 312 is a member of the &, and so the formula of the class is B3G%
Volume 57. Number 12. December 1980 1 879
