Question

A basic amino acid,arginine,has a molar mass of 174g.mol^-1.it has the following percentage composition:41,38% carbon, 18,39% of oxygen,32,18% of nitrogen and 8,O5% of Hydrogen.determine the molecular formular of arginine

Answer 1

Take a 100 g sample which gives you
41.38g C
18.39g O
32.18g N
8.05g H

Convert to mols.
41.38/12 = approx 3.5
18.39/16 = approx 1.15
etc.

Then find the ratio of the atoms to each other with the smallest value being 1.00. The easy way to do that is to divide the smallest number by itself; thereby forcing it to be 1.00. Then divide all of the other numbers by that same small number. Round to whole numbers. That gives you the empirical formula. To find the molecular formula do this.
Find the empirical mass (that's the same as the molar mass assuming the empirical formula is the molecular formula). Then empirical mass x ?whole number = 174
Solve for ?whole number, round to the nearest whole number and that is the muleiplier for the empirical formula; i.e., (CxHyOzNw)_{whole number}
Post your work if you have trouble.