Find the molecular formula for estriol?

we use the mass of carbon dioxide to work out the mass of carbon

molar mass of CO2 = 44 g/ mole

36.86 g of CO2 has 36.860 /44 = 0.83773 moles of CO2

there is 1 mole of C in CO2 and all the C from the compound becomes CO2

so moles of C in the compound = 0.83773 moles

mass of C = 0.83773 x 12 = 10.06697 g

we use the mass of water to find out the mass of hydrogen

molar mass of H2O = 18 g/ mole

10.06 g of H2O has 10.0600 / 18 = 0.55842 moles of H2O

there are 2 moles of H in H2O so moles of H in the compound = 1.11683 moles

mass of H = 1.11683 x 1.0079 = 1.1257 g

we calculate the O by difference from the mass of sample once we know the mass of C and H

mass of H + C = 11.19263 g

mass of sample = 13.420 g

mass of O by difference = 2.22737 g

moles of O = 2.22737 /16 = 0.13921 moles

we now work out the molar ratio of all the elements in the compound

molar ratio of C : H : O = 0.83773 : 1.11683 : 0.13921

smallest number 0.13921

divide the ratio by the smallest number we get

molar ratio of C : H : O = 6.0 : 8.0 : 1.0

empirical formula is C6H8O

this has a formula mass of 72+8+16 = 96g

to find the number of empirical units in a mole of compound we divide the molar mass by the formula mass

= 288.38 / 96 = 3.0

so the molecular formula of estriol is 3 x the empirical formula or C18H24O3

there is your solution ..