Question

An antibiotic, which is also used as an anticancer drug, was isolated from Streptomycetes bacteria. Its elemental analysis gives the following composition (by weight):

%C 57.89

%H 6.87

%N 13.97

%O 21.27

The formula weight is found (in a seperate experiment) to be NEAR 1300g/mole. Determine the MOLECULAR FORMULA of the antibiotic. show ALL work.

Answer 1

You have a total of 1300g/mole for the complete antibiotic. From the percentages that are given to you, you can calculate the amount of each element in the formula. Now, see the molecular weight of esch of the elements, as follows:

C - 12.0107 g/mole

H - 1.00794 g/mole

N - 14.0067 g/mole

O - 15.9994 g/mole

Now use the percentages to know the total mass per element:

Carbon: (57.89%)(1300g/mole)/100% = 752.57g/mole

Now divide this last quantity over the molecular weight of the element alone:

752.57 / 12.0107= 62.65

Hydrogen: (6.87%)(1300g/mole)/100%= 89.31g/mole

89.31/1.00794= 88.61

Nitrogen: (13.97%)(1300g/mole)/100%= 181.61g/mole

181.61/14.0067= 12.97

Oxygen: (21.27%)(1300g/mole)/100%= 276.51g/mole

276.51/15.9994= 17.28

Now, as it is stated that the molecular weigiht is near 1300 but it is not exact, you can round the amount of atoms of each element as:

C₆₃H₈₉N₁₃O₁₇