Given the following data, calculate the molar mass. Barometric pressure: 639.4 mm Hg Mass of...

Question:

Given the following data, calculate the molar mass.

Barometric pressure: 639.4 mm Hg

Mass of the flask and foil: 79.5 g

Mass of the flask, foil, and condensed liquid: 81.4 g

Volume of flask: 125.8 mL

Temperature of water bath: 99.9 degree C

Answer:

Ideal Gas Law

The ideal gas law can be used to model gas behaviors by relating its pressure, volume, amount in moles and temperature. Though it is not perfect, it does give pretty good approximation under common conditions. The ideal gas law is expressed as PV = nRT, where R is the universal gas constant.

Answer and Explanation:

{eq}molar\;mass=550.\;g/mole {/eq}

This is the Dumas method for molar mass of gas determination where a volatile liquid is heated to vaporize and allowed to fill a container. Then left to cool so the amount of gas in the container can be determined by weighing. Then using ideal gas law, the moles of gas can be calculated. Along with the calculated moles and measured mass, molar mass can be calculated.

Pressure

$$639.4\;mmHg \times \frac {1\;atm}{760\;mmHg} = 0.841\;atm $$

Volume

$$125.8\;mL \times \frac {1\;L}{1000\;mL} = 0.1258\;L $$

Temperature

$$99.9\;^oC +273.15 = 373.05\;K $$

Mass of gas$$81.4\;g - 79.5\;g = 1.9\;g $$

Moles of gas (n) is calculated using the idea gas law

$$PV = nRT $$

$$n = \frac {PV}{RT} $$

$$n = \frac {(0.841\;atm)(0.1258\;L)}{(0.0821 \frac {atm \cdot L}{mole \cdot K})(373.05\;K)} =0.003456\;mole $$

The molar mass is then

$$\frac {1.9\;g}{0.003456\;mole} = 550.\;g/mole $$


Learn more about this topic:

Loading...
What is Molar Mass? - Definition, Formula & Examples

from General Studies Science: Help & Review

Chapter 27 / Lesson 24
555K

Related to this Question

Explore our homework questions and answers library