Question

A 0.8715 g sample of sorbic acid, a compound first obtained from the berries of a certain ash tree, is burned completely in oxygen to give 2.053 g of carbon dioxide and 0.5601 g of water. the empirical formula of sorbic acid is

Answer 1

Answer;

C3H4O

Explanation;

Empirical formula is the simplest formula of a compound;

Molar mass CO2 = 44.01  

Mass of CO2 produced = 2.053 g

Mass of carbon in original sample = 12.01/44.01 × 2.053

                                                           = 0.5603g  

Molar mass H2O = 18  

Mass of H in original sample = 2/18 ×0.5601

                                               = 0.0622  g

Thus; original sample contained 0.5603g C and 0.0622g H. The balance of the sample was O  

Mass of O = 0.8715 - (0.5603 + 0.0622) = 0.249g  

The mole ratio of C:H:O  will be;

Moles C = 0.5603/12 = 0.0467  

Moles H = 0.0622  

Moles O = 0.249/16 = 0.01556  

C:H:O = 0.0467:0.0622:0.01556  

Divide through by 0.01556:  

C:H:O = 3:4:1  

Empirical formula is thus C3H4O

Answer 2

Answer:

C₃H₄O is the empirical formula of ascorbic acid

Explanation:

First, we need to write the reaction. I will call the Ascorbic Acid as AA:

AA + O₂ ------> CO₂ + H₂O

We know we have initially 0.8715 g of AA, and this produces 2.053 g of CO₂ and 0.5601 g of H₂O.

From the products, we can calculate how many moles of each element (C, H and O) has the ascorbic acid.

So, let's take in mind the molecular weight of CO₂ and H₂O:

MWCO₂ = 44 g/mol

MWH₂O = 18 g/mol

From the molecular weight we can calculate the moles of each product:

moles CO₂ = 2.053 / 44 = 0.0467 moles

moles H₂O = 0.5601 / 18 = 0.0311 moles

Now, with this, we can do a mole ratio of the elements. In the case of CO₂, we can calculate how many grams of Carbon are in the ascorbic acid, and with the water, the grams of hydrogen. Then, with difference we can get the mass of oxygen.

To do this ratio, we do a rule of 3.

To Carbon:

12 g C --------> 44 g CO₂

X g C ---------> 2.053 g CO₂

X = 2.053 * 12/44 = 0.5599 g of C

For Hydrogen:

2 g H ------> 18 g H₂O

X g H ------> 0.5601 g H₂O

X = 2 * 0.5601/18 = 0.0622 g of H

We have the mass of C and H, so the grams of oxygen are:

m O = 0.8715 - 0.0622 - 0.5599 = 0.2494 g of O

Now that we have the mass of each element, we can calculate the empirical formula following 3 steps.

Step 1: Calculate the moles of each element

C = 0.5599 / 12 = 0.0467

H = 0.0622 / 1 = 0.0622

O = 0.2494 / 16 = 0.0156

Step 2: Calculate the mole ratio

Doing this, is just dividing all the moles by the smallest number of moles obtained. In this case, the oxygen so:

C = 0.0467/0.0156 = 2.99

H = 0.0622/0.0156 = 3.99

O = 0.0156/0.0156 = 1

These results represent the number of atoms of each element in the empirical formula, so the last step is write the empirical formula with the previous results, rounding the numbers to get an even number so:

C₃H₄O

This would be the empirical formula of ascorbic acid.