The mass of an evacuated 255 mL flask is 143.187 g. The mass of the flask filled with 267 torr of an unknown gas at 25 °C is 143.289 g. Calculate the molar mass of the unknown gas.

Video transcript

Hi everyone here we have a question telling us that a 250 millimeter evacuated flask has a mass of 112.78 g when filled with 378 tour of an unknown gas at 29.0 degrees Celsius. And our question is, what is the molar mass of the unknown gas? If the mass of the 250 millimeter evacuated flask is 112.36 g, So we know that our volume is millimeter and we want to change that to leaders. So we're going to multiply by one leader Over 1000 ml And our middle leaders are going to cancel out, giving us 0.250 L. And the mass of our gas Equals 112. minus 112.36. So that equals 0.42 g. And we know that density equals mass over volume. So our density Is going to equal 0.42 g Divided by 0.250 L. And that equals 1.68. Our pressure Equals 378 Tour and we need to change that to atmosphere. So we're going to multiply by one atmosphere Over 760 tour and our tours are going to cancel out. And that is going to equal 0. atmospheres. Our temperature Equals 273. plus 29. And we added the 273.15. Because we need it in Kelvin And that equals 302.15. And our density equals pressure times molar mass over r gas constant times our temperature. So if we rearrange that our molar mass equals density times our gas constant times our temperature overpressure. So our molar mass is going to equal 1.68 grams per leader Times 0. Times 302.15 Kelvin, and that is divided by 0. Atmospheres And that equals 83.74 g per mole. So that is our final answer. Thank you for watching. Bye.