Lesson 4: 3.4 Ideal Gas Law

How does changing one property of a confined gas affect its other physical parameters?
How can the ideal gas equation (PV = nRT) be rearranged to calculate the density or molar mass of an unknown gas?

Hydrostatic Pressure
Kelvin Temperature
Universal Gas Constant
Volatile
Absolute Zero

Learning Objective 3.4.A; Suggested Skill 5.C (Mathematical Routines).

Introduces the mathematical treatment of gases. Students must be comfortable solving for individual variables, adapting to different units of pressure (atm, torr, mmHg) by matching the correct value of the universal gas constant (R), and manipulating the formula to discover density (d = PM/RT).

Support: Provide an algebraic variable-tracking table for students to fill out before plugging values into the equation (e.g., P = ..., V = ..., n = ...).
Extension: Have students derive the molar mass equation (M = mRT/PV) directly from PV = nRT and substitution of n = m/M, explaining the physical units cancelation.

An unknown volatile liquid is vaporized inside a 0.250L flask at a temperature of 99.0 degrees C and a pressure of 0.974atm. The mass of the vaporized gas is measured to be 0.563 g. Calculate the molar mass of the unknown substance.