Problem: Terephthalic acid is an important chemical used in the manufacture of polyesters and plasticizers. It contains only C, H, and O. Combustion of 19.81 mg terephthalic acid produces 41.98 mg CO2 and 6.45 mg H2O. If 0.250 mole of terephthalic acid has a mass of 41.5 g, determine the molecular formula for terephthalic acid.

FREE Expert Solution

We’re being asked to determine the molecular formula of a terephthalic acid composed of C, H, and O given the combustion analysis.


Recall that in combustion analysisa compound reacts with excess O2 to form products


For a compound composed of C, H, and O, the reaction looks like this:


CxHyOz + O2 (excess)  x CO2y H2O


This means we need to do the following steps:

Step 1: Calculate the mass of C and H in the compound.

Step 2: Calculate the mass of O in the compound.

Step 3: Determine the lowest whole number ratio of C, H, and O to get the empirical formula.

Step 4: Use the empirical mass to calculate the molecular formula


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Problem Details

Terephthalic acid is an important chemical used in the manufacture of polyesters and plasticizers. It contains only C, H, and O. Combustion of 19.81 mg terephthalic acid produces 41.98 mg CO2 and 6.45 mg H2O. If 0.250 mole of terephthalic acid has a mass of 41.5 g, determine the molecular formula for terephthalic acid.

Frequently Asked Questions

What scientific concept do you need to know in order to solve this problem?

Our tutors have indicated that to solve this problem you will need to apply the Combustion Analysis concept. You can view video lessons to learn Combustion Analysis. Or if you need more Combustion Analysis practice, you can also practice Combustion Analysis practice problems.

What professor is this problem relevant for?

Based on our data, we think this problem is relevant for Professor Rubin's class at UCSC.

What textbook is this problem found in?

Our data indicates that this problem or a close variation was asked in Chemistry: An Atoms First Approach - Zumdahl Atoms 1st 2nd Edition. You can also practice Chemistry: An Atoms First Approach - Zumdahl Atoms 1st 2nd Edition practice problems.