Final answer:
Without additional information such as temperature, volume, or molar amounts, it is not possible to calculate the partial pressure of helium in the mixture using Dalton's law of partial pressures.
Step-by-step explanation:
The partial pressure of helium in the mixture can be calculated using Dalton's law of partial pressures, which states that the total pressure of a mixture of non-reacting gases is equal to the sum of the partial pressures of individual gases. Given a total pressure of 445 torr and a mixture of helium and neon, we need to find the ratio of helium to the total mixture to determine its partial pressure.
However, the question does not provide enough information to determine the partial pressures using just the masses (250 mg of helium and 345 mg of neon) alone. To find the partial pressures, we would need to know the volume of the container and the temperature of the gases or the molar amounts of each gas. Only with this additional information could we apply the ideal gas law to each gas, and then use the ratios of the mole fractions in the mixture to calculate the partial pressure.
It's important to remember that partial pressure is proportional to the mole fraction of the gas in the mixture when temperature and volume are constant. Thus, without the mole fractions or any additional data regarding temperature or volume, we are unable to calculate the partial pressure of helium directly.