Question

A sample of oxygen is collected in a 335 mL container over water at 15℃, and the barometer reads 752 torr. What volume would the dry gas occupy at 755 torr and 15℃? Water’s partial pressure at 15◦C is 12.8 torr.

Answer 1

To find the volume of dry oxygen at 755 torr and 15℃, subtract the water vapor pressure from the total pressure to get the pressure of dry oxygen, and apply the combined gas law while keeping temperature constant.

Step-by-step explanation:

The question is related to finding the volume of a gas under different conditions using the gas laws, specifically considering the partial pressures when a gas is collected over water. We have a sample of oxygen collected over water at 15℃ with a barometer reading of 752 torr. The water vapor pressure at this temperature is 12.8 torr. To find the volume of dry oxygen gas at 755 torr and 15℃, we first calculate the pressure of dry oxygen by subtracting the water vapor pressure from the total pressure. Then, we can apply the combined gas law to find the new volume, since temperature remains constant.

The calculation can be done as follows:

1. Calculate the pressure of dry oxygen: P₀₂ = Total pressure - Water vapor pressure = 752 torr - 12.8 torr = 739.2 torr.
2. Use the combined gas law since temperature is constant (V₁P₁ = V₂P₂), rearrange to solve for V₂: V₂ = V₁(P₁/P₂). Here, V₁ is the original volume, P₁ is the pressure of dry oxygen, and P₂ is the new pressure (755 torr).
3. Insert the values and calculate the new volume: V₂ = 335 mL (739.2 torr / 755 torr).
4. Solve for V₂ to find the volume of dry gas.