Standard Temperature and Pressure Video Lessons

Concept: Standard Temperature and Pressure

# Problem: An organic compound contains C, H, N, and O. Combustion of 0.1023 g of the compound in excess oxygen yielded 0.2766 g CO2 and 0.0991 g H2O. A sample of 0.4831 g of the compound was analyzed for nitrogen by the Dumas method (see Exercise 129). At STP, 27.6 mL of dry N2 was obtained. In a third experiment, the density of the compound as a gas was found to be 4.02 g/L at 127°C and 256 torr. What are the empirical and molecular formulas of the compound?

###### 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

An organic compound contains C, H, N, and O. Combustion of 0.1023 g of the compound in excess oxygen yielded 0.2766 g CO2 and 0.0991 g H2O. A sample of 0.4831 g of the compound was analyzed for nitrogen by the Dumas method (see Exercise 129). At STP, 27.6 mL of dry N2 was obtained. In a third experiment, the density of the compound as a gas was found to be 4.02 g/L at 127°C and 256 torr. What are the empirical and molecular formulas of the compound?