Question

Para-cresol, a substance used as a disinfectant and in the manufacture of several herbicides, is a molecule that contains the elements carbon, hydrogen, and oxygen. Complete combustion of a 0.345-g sample of p-cresol produced 0.983 g carbon dioxide and 0.230 g water. Determine the empirical formula for p-cresol.

Short answer

The empirical formula for p-cresolis C₇H₈O .

Step-by-step solution

Definition

A chemical formulathat shows the simplest ratio of elements in a compound rather than the total number of atoms in the molecule is known as an empirical formula.

Determination of mass of O2

From the given, we have the chemical reaction:

$CHO+O_2\to C{O}_2+H_{2}O$(Unbalanced)

The mass on both sides of the equation is equal since the reaction is complete.

Here the mass of O₂: 0.983g + 0.230g - 0.345g

= 0.868g

Determination of mass of C

We can observe that only CHO has C atom on the left side, while only CO₂ has C atom on the right side. This indicates that CHO has the same amount of carbon as CO₂ :

$$\begin{gathered} 0.983gC{O}_2\times \frac{1mol}{12.01g+16.00g\times 2}\times \frac{1molC}{1molC{O}_2} \\ =0.0223molC \end{gathered}$$

Here the mass of C,

$$\begin{gathered} =0.0223mol\times \frac{12.01g}{1mol} \\ =0.268g \end{gathered}$$

Determination of mole of O

The mole of H in water is similar in CHO :

$$\begin{gathered} 0.230g{H}_{2}O\times \frac{1MOL{H}_{2}O}{1.01G\times 2+16.00g}\times \frac{1molH}{1mol{H}_{2}O} \\ =0.0255gH \end{gathered}$$

Mass of O in CHO ,

= 0.345 g - 0.268 g - 0.0255 g

= 0.0515 g

Mole of role="math" localid="1655358195763" $O:0.0515g\times \frac{1mol}{16.00g}$

= 0.00322 mol

Determination of Empirical formula of p-cresol

Thus, 0.0223 mol C, 0.0255 mol H, and 0.00322 mol O.

From the above, it is concluded that O has the lowest mol. Let’s divide the all three by the mol of O.

Here, 6.928 mol C, 7.922 mol H, and 1 mol O.

Let’s round up,

7 mol C, 8 mol H, and 1 mol O

Therefore the Empirical formula is C₇H₈O.