# Caffeine formula

chawki

## Homework Statement

Caffeine, a stimulant found in coffee, tea, chocolate, and some medications,
contains 49.48% carbon, 5.15% hydrogen, 28.87% nitrogen, and 16.49% oxygen
by mass and has a molar mass of 194.2.

## Homework Equations

Determine the molecular formula of caffeine.

## The Attempt at a Solution

CxHyNzOn
12x/C% = 194.2/100% and we find x = 8
by the same method we do it for H, N and O and we find y=10, z=4, n=2
so the formula is C8H10N4O2

Plz tell me if i should add something to my solution in the beginning, like the name of this law, i forgot how we called it at college...

## Answers and Replies

DDTea
You did this right.

Here's a cool trick; it may be useful in the future. It's called the "nitrogen rule" (or at least that's what we called it): if the molecule has a and odd molar mass, there is an odd number of nitrogen atoms in the structure (usually 1, but sometimes 3, 5, etc.). If it is even, there are either NO nitrogens or 2, 4, 6, etc.

chawki
ok wow, but how we call this law that i used in solution