edited by: JOHN J . ALEXANDER University of Cincinnati Cincinnati. Ohio 45221
exam que~tion exchange Molecular Weights Come of Age J. Tietjen Oueensbarough Community Callege Bayside. NY 11364 A b i t of logic a n d a bit of chemistry solves t h e puzzle. T h e chemical knowledge required is t h a t of t h e general chemistry course. Question S i x chemists were seated a r o u n d a table. E a c h was a specialist in a major field of chemistry; Bill, Richard, Barbara, Alice, James, a n d T o m were each ( n o t respectively a n d n o t necessarily seated in the listed order), an organic chemist, an analytical chemist, a n inorganic chemist, a physical chemist, a hiochemist, a n d a polymer chemist. E a c h chemist h a d i n f r o n t of h i m or her a sealed jar of a chemical whose molecular weight was identical to t h a t chemist's age. Identify t h e n a m e , field of specialty, a n d age of e a c h chemist. Clues: 1. The analytical chemist noted that the chemical in front of Riehard had a rate of effusion twice as slow as methane. 2. The biochemist, a woman, had a compound whose empirical and
molecular formula were identical and was composed of 81.82% C and 18.18%H by weight. 3. The woman sitting on Bill's right had a liquid whose vapor pressure was lowered 4% when 0.1 mol of sugar was dissolved into 84 g of the liauid. 4 . Tom, the polymer chemist, was5yearsolder than Alice. When 4 g ~ n f Tom's c hemiral inanel~ctrolgw, was dissolved in 20 g of HzO, IKI,. for H,O = 0.52,. the sdut:on hcilcd at l(r2.6 .-,. Thp inurannir chemist. Jnmrs, n o t 4 that Hill was not a physical chemist, and Bdl was 2 years older than the analytical chrmist; 11 2;ItiX c uf Bill's uhemicnl ( a aohd monnnrotie acid1 was ablr to . neutral';ze 8 m~ of 0.40 M c ~ ( o H ) ~ . 6. James, the youngest, had a 2-carbon hydrocarbon. When a portion of i t was burned in oxygen, 52.8 g of COz and 10.8 g of Hz0 were produced.
-96% - mole fracti~n~~,~,,,, 100% 0.96 = male fractionraoivent, 0.96 =
molesrsoiwn,l molesrd,",1+0.1 molesr,d,"tl
= 2.4
ma88 moles = MW
84 2.4 = MW
MW = 35 Conclusions: Either Barbara or Alice was 35 years old
4. ATh, = Khp. mohlity
since water normally boils a t 100 'C, ATb = 2.6 MW = 40
4 mw 2.6 = 0.52 -
nnm
Conclusions: Tom was 40 years old and a polymer chemist. Alice was 35 years old. Barbara was 44 years old and the hiochemist. 5. Moles acid = moles base
-v
Acceptable Solutlon
Conclusions: Bill was 37 years old. James was an inorganic chemist. Alice was the anal&al chemist. Since the biochemist, inorganic chemist, polymer chemist, and analvtical chemist have been identified and Bill was not a physical chemist, Bill was an organic chemist and Richard a physical chemist.
+
Conclusions: Richard was 64 years old. Richard was not the analytical chemist 2. 81.82 g C : 18.18 g H
81.82C:18.18H 12 1
+
6. CzH, + 0 2 COz Hz0 52.8 52.8 g COI = -= 1.2 mol C 0 2or 1.2 mol C 44 10.8 10.8 g Hz0 = -= 0.6 mol H 2 0 or 1.2 m d H 18 The original 2-carbon hydrocarbon had equal numbers of C and H atoms. The hydrocarbon was C2Hz. MW = 26 Conclusion: James was 26 years old.
Summary 1 C: 2.666 H (multiply by 3) 3C:BH C,H, empirical and molecular formula MW = 44
Conclusions: The hiochemist was 44 years old and was either Barbara or Alice.
Name
Specialty
Age
Tom Richard Alice
Polymer chemist Physical chemist Analytical chemist Organic chemist Biochemist Inorganic chemist
40 64 35 37 44 26
Bill
Barbara James
Volume 64
Number 5
May 1987
401
