Question

The simplest formula for vitamin C is C3H4O3. Experimental data indicates that the molecular mass of vitamin C is about 180. What is the molecular formula of vitamin C?

Answer 1

Start by working out the masses of the atoms in the simplest (empirical) formula: (3 x 12) + (4 x 1) + (3 x 16) = 88

So the relative formula mass is a multiple of 88. To see which multiple, we divide the experimental `M_r` by the empirical formula mass. 180/88 = 2.04 and round this to a whole number = 2

So the molecular formula is 2x the simplest formula: `C_6H_8O_6` giving an `M_r` of 176 which is close to the experimental value.