Respuesta :
The empirical formula of the carboxylic acid is C₃H₆O₂.
For determination of the empirical formula of the carboxylic acid we need to determine the number of carbon, hydrogen and oxygen atoms present in the sample.
As you know, one mole of water, contains 2 moles of hydrogen. This means that the percent composition of hydrogen in water will be
2× 1.00794 g/mol / 18.015 g/mol × 100 = 11.19% H
What this means is that every 100 g of water will contain 11.19 g of hydrogen. In your case, the 0.2349-g sample of water will contain
0.2349 g water⋅ 11.19 g H / 100 g water = 0.026285 g H
Similarly, one mole of carbon dioxide, CO₂, contains one mole of carbon. The percent composition of carbon in carbon dioxide will be
1 ×12.011 g/mol / 44.01 g/mol × 100 = 27.29% C
Once again, this tells you that every 100 g of carbon dioxide will contain
27.29 g of carbon. In your case, you will have
0.5706g H₂O ⋅ 27.29 g C /100g H₂O = 0.15572 g C
The mass of carbon + hydrogen originally present in the carboxylic acid sample will be
m C + H = 0.026285 g + 0.15572 g =0.18201 g
The initial mass of the sample was equal to 0.3200 g. This tells you that the sample also contains oxygen
m oxygen = 0.3200 g −0.18201 g = 0.13799 g O
So, now that you know how many grams of each element were present in the initial sample, use their molar masses to convert these to moles
For C: 0.15572g /12.011g/mol = 0.012965 moles C
For H: 0.026285 g/1.00794g/mol = 0.026078 moles H
For O: 0.13799g/15.9994g/ mol = 0.0086247 moles O
Now, to get the compound's empirical formula, you need to find the smallest whole number ratio that exists between the number of moles of each element in the compound.
To do that, divide these values by the smallest one to get
For C: 0.012965 moles / 0.0086247 moles = 1.5032 ≈ 1.5
For H: 0.026078moles /0.0086247 moles =3.0236≈ 3
For O: 0.0086247moles /0.0086247 moles = 1
This means that you have
C₁.₅H₃O₁
Since you're looking for the smallest whole number ratio that exists between the elements, multiply each subscript by 2 to get
C₁.₅H₃O₁ * 2 = C₃H₆O₂
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