a compound has an empirical formula CH20 and molecular mass of 90 determine it's molecular formula(H=11; C=12; 0=16)

Answer 1

empirical mass CH2O is 12 + 2 + 16 = 30
The molar mass is 90.
empirical mass x #units = molar mass
30*units = 90
so you must have (CH2O)3 or
C3H6O3. Check it.
3*12 = 36
6*1 = 6
3*16 = 48
48 + 6 + 36 = 90