# Problem: Researchers obtained the following data from experiments to find the molecular formula of benzocaine, a local anesthetic, which contains only carbon, hydrogen, nitrogen, and oxygen. Complete combustion of a 3.54-g sample of benzocaine with excess O2 forms 8.49 g CO2 and 2.14 g H2 O. Another 2.35 g sample contains 0.199 g of N. The molar mass of benzocaine is 165 g/mol.Find the molecular formula of benzocaine.

###### FREE Expert Solution

Step 1: Determine the mass of C and H produced from the reaction

So the mass of C from 8.49 g CO2 is

= 2.3169 g C

So the mass of H from 2.14 g H2O is

= 0.2395 g H

Step 2: Determine the mass percent of C, H and N

Recall that mass percent is given by:

= 65.4492 % C

= 6.7655 % H

= 8.4681 % N

Step 3: Determine the mass and moles C, H, O and N from their mass percent

%C + %H + %O + %N = 100%

%O = 100% – (% C + % H + %N)

%O = 100% - (65.4492 %C + 6.7655% H + 8.4681% N)

%O = 19.3172 % O

Assuming we have 100 g of the compound, this means we have 65.4492 g C, 6.7655 g H, 8.4681 g N and 19.3172 g O

5.4496 mol C

= 6.6585 mol H

= 0.6044 mol N

= 1.2073 mol O

Step 4: Determine the lowest whole number ratio of C, H, O and N to get the empirical formula

9 C

11 H

1 N

2 O

The empirical formula of benzocaine is C9H11NO2

Step 5: Determine the molecular formula

84% (477 ratings) ###### Problem Details

Researchers obtained the following data from experiments to find the molecular formula of benzocaine, a local anesthetic, which contains only carbon, hydrogen, nitrogen, and oxygen. Complete combustion of a 3.54-g sample of benzocaine with excess O2 forms 8.49 g CO2 and 2.14 g H2 O. Another 2.35 g sample contains 0.199 g of N. The molar mass of benzocaine is 165 g/mol.

Find the molecular formula of benzocaine.

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