Question

A sample of carbon monoxide was collected over water at a total pressure of 756 torr and a temperature of 18°C. What is the pressure of the carbon monoxide sample?

Short answer

The carbon monoxide sample has a pressure of 740.5 torr.

Step-by-step solution

Step 1: Definition of pressure

The force of all gas particle/wall collisions divided by the area of the wall equals the pressure (P). Pressure is one of the fundamental quantities of this phase of matter, and it is exerted by all gases.

Calculate pressure of carbon monoxide

According to Dalton's law, the total pressure of 756 torr is the sum of the partial pressures of carbon monoxide (CO) and gaseous water. Hence

$$P_{\mathrm{T}}=P_{\mathrm{C}\mathrm{O}}+P_{{\mathrm{H}}_2\mathrm{O}}$$

Rearranging this equation to solve for the pressure of carbon monoxide gives:

$$P_{\mathrm{C}\mathrm{O}}=P_{\mathrm{T}}-P_{{\mathrm{H}}_2\mathrm{O}}$$

From Table 9.2, the pressure of water vapour above a sample of liquid water at18°Cis 15.5torr. So:

$$\begin{array}{r}{P}_{\mathrm{C}\mathrm{O}}=756\mathrm{t}\mathrm{o}\mathrm{r}\mathrm{r}-15.5\mathrm{t}\mathrm{o}\mathrm{r}\mathrm{r}\\ =740.5\mathrm{t}\mathrm{o}\mathrm{r}\mathrm{r}\end{array}$$

Thus the pressure of carbon monoxide is 740.5 torr.