Final answer:
The student is asked to calculate the volume of a nitrogen gas sample when collected over water at a different temperature and pressure, requiring knowledge of Dalton's law and the ideal gas law.
Step-by-step explanation:
The question involves calculating the volume of a gas sample (nitrogen) when collected over water at a certain temperature and pressure. This is a common type of problem in chemistry that requires an understanding of the gas laws, particularly Dalton's law of partial pressures and the ideal gas law. The volume of a nitrogen sample at standard temperature and pressure (STP) is given, and we are asked to find what the volume would be at 25°C and 750 torr when collected over water.
At STP (0°C, 1 atm), the volume of the nitrogen sample is 249 mL. To find the new volume at 25°C (which is 298 K when converted to Kelvin) and 750 torr, we must account for the vapor pressure of water at 25°C, which can be found in a table of vapor pressures. Using Dalton's law, we subtract the vapor pressure of water at 25°C from the total pressure to get the partial pressure of nitrogen. Then we can use the ideal gas law (PV=nRT) to find the new volume. Since the number of moles of nitrogen does not change, and the gas constant R is a constant, we can set up a ratio between the initial and final conditions of the gas sample to solve for the final volume.