Problem 12P
Compute the empirical and molecular formulas for each of the following elemental analyses. In each case, propose at least one structure that fits the molecular formula.
C 
H 
N 
C1 
MW 

(a) 
40.0% 
6.67% 
0 
0 
90 
(b) 
32.0% 
6.67% 
18.7% 
0 
75 
(c) 
25.6% 
4.32% 
15.0% 
37.9% 
93 
(d) 
38.4% 
4.80% 
0 
56.8% 
125 
Solution 12P
(a) For the unknown compound, we do the following computations
The first computation divides the number of grams of carbon by 12, the number of grams of hydrogen by 1, and the number of grams of oxygen by 16. We compare these numbers by dividing then by the smallest number, 3.33. The final result is ratio of one carbon to two hydrogens to oxygen. This result gives the empirical formula or . The given molecular weight is 90, so our unknown compound must contain thrice this may atoms. The molecular formula must be 3() =
(b) For unknown compound, we do the following computations:
This result given the empirical formula .
The weight of one unit is 75 and the given molecular weight is 75, so the molecular formula must be .
(c) For unknown compound, we do the following computations:
This result gives the empirical formula and the weight of one NOCl unit is 93. The given molecular weight is also 93, so the molecular formula of unknown compound must be NOCl .
(d) We do the following computations:
This result gives the empirical formula and weight of one unit is 62.5. The given molecular weight is 125, so out unknown compound must contain twice this many atoms.
The molecular formula must be