A hydrocarbon is burnt completely to give 3.447g of #sf(CO_2)# and 1.647g of #sf(H_2O)#. What is the empirical formula ?

Question

Peyton Adams · Accepted Answer

The empirical formula is #C_3H_7#. Convert moles to grams by dividing by the #M_r#: Moles #CO_2 = 3.447/44.01=0.0783# Moles #H_2O=1.647/18.01=0.0914# Moles #C=0.0783# Moles#H=0.0914xx2=0.1829# Ratio #C:H# by moles = #0.0783:0.1829rArr# #1:2.33rArr# #3:7#  So the empirical formula is #C_3H_7#

Owen Ambrose · Answer

Your compound's empirical formula is #C_3H_7#.

I'll demonstrate a different method for determining how many moles of hydrogen and carbon the hydrocarbon sample contained.

This technique makes use of the percentages of carbon and hydrogen in water and carbon dioxide, respectively.

So, you know that the combustion reaction produces 3.447 g of carbon dioxide. If you use the molar mass of carbon and that of carbon dioxide, you can determine the percent composition of carbon in #CO_2#.

#(12.0cancel("g/mol"))/(44.0cancel("g/mol")) * 00 = "27.27% C"#

This means that, for every 100 g of #CO_2#, you get 27.27 g of carbon. This means that the mass of carbon in the original hydrocarbon was

#3.447cancel("g"CO_2) * "27.27 g C"/(100cancel("g"CO_2)) = "0.9400 g C"#

Apply the same principle to hydrogen and water, but remember that each water molecule yields two hydrogen atoms.

#(2 * 1.01cancel("g/mol"))/(18.02cancel("g/mol")) * 100 = "11.21% H"#

Given that 11.21 g of hydrogen will be present in every 100 g of water, your hydrocarbon contained

#1.647cancel("g"H_2O) * "11.21 g H"/(100cancel("g"H_2O)) = "0.1846 g H"#

Now, calculate how many moles of each you have using the molar masses of hydrogen and carbon.

#"For C": (0.9400cancel("g"))/(12.0cancel("g")/"mol") = "0.07833 moles C"#

#"For H": (0.1846cancel("g"))/(1.01cancel("g")/"mol") = "0.1828 moles H"#

Once more, calculate the mole ratio of carbon to hydrogen in the hydrocarbon by dividing both numbers by the smallest one.

#"For C": (0.07833cancel("moles"))/(0.07833cancel("moles")) = 1#

#"For H": (0.1828cancel("moles"))/(0.07833cancel("moles")) = 2.33#

Your sample included

#C_1H_2.33#

To eliminate the fractional subscript, multiply by three.

#C_3H_7# #-># your compound's empirical formula.

Henry Antrim · Answer

undefined To determine the empirical formula, first, find the moles of carbon dioxide and water produced using their respective molar masses. Then, determine the ratio of the elements (carbon and hydrogen) in the compound using these moles. Finally, express the ratio in the simplest whole-number ratio to obtain the empirical formula.

1. Calculate moles of carbon dioxide (CO2):
   - Moles of CO2 = mass of CO2 / molar mass of CO2

2. Calculate moles of water (H2O):
   - Moles of H2O = mass of H2O / molar mass of H2O

3. Determine the ratio of carbon to hydrogen by comparing the moles obtained from steps 1 and 2.

4. Express the ratio in the simplest whole-number form to obtain the empirical formula.