Question

Estrone, which contains only carbon, hydrogen, and oxygen, is a female sexual hormone that occurs in the urine of pregnant women. combustion analysis of a 1.893-g sample of estrogen produced 5.543 g of co2 and 1.388 g h2o. the molar mass of estrogen is 270.36 g/mol . part a find the molecular formula for estrone.

Answer 1

Answer;

Molecular formula = C18H22O2

Explanation and solution;

All the C from the sample ends up in the CO2. SO if we find moles of CO2 produced we can determine moles of C that was in the sample.  

Moles CO2 = mass / molar mass  

= 5.543 g / 44.01 g/mol = 0.12595 mol CO2  

Then we can use this to find the mass of C  

mass = molar mass x moles  

= 0.12595 mol x 12.01 g/mol  

= 1.5127 g C  

All the H ends up in the H2O  

moles H2O = 1.388 g / 18.016 g/mol  

= 0.07704 moles H2O  

Each H2O has 2 H atoms  

So; moles H = 2 x moles H2O  

= 0.15409 moles H  

Mass H = 0.15409 mol x 1.008 g/mol  

= 0.1553 g H  

Mass O = mass sample - mass C - mass H  

= 1.893 g - 1.5127g - 0.1553 g  

= 0.2250 g O  

Moles O = 0.2250 g / 16.00 g/mol  

= 0.0140625 mol  

Now ratio C : H : O  

= 0.12595 : 0.15409 : 0.0140625  

Divide each number in the ratio by the smallest number  

    C : H : O  

(0.12595 / 0.0140625) : (0.15409/ 0.0140625) : (0.0140625/ 0.0140625)  

= 9 : 11 : 1  

Empirical formula  

C9H11O  

To find molecular formula divide molar mass by mass of empirical formula, this tells you how many times the empirical formula fits in the molecular formula  

= 270.36 g/mol / 135.178  

= 2  

Molecular formula = empirical formula x 2  

= C18H22O2