A 0.286-g sample of gas occupies 125 ml at 60. cm of hg and 25°

c. what is the molar mass of the gas?

Using the Equation: PV=nRT

Where P is the pressure 60 cmHg or 600 mmHg or 600/760 = 0.789 atm

V is the volume 125 ml or 0.125 L, n is the number of moles, R is a constant 0.082057, and T is temperature 25 °C or 298 K;

Therefore:

0.789 * 0.125 = n * 0.082057 * 298

n = 0.0987/24.45

= 0.004036 mol

0.004036 mole has a mass of 0.286 g

Hence; 1 mole has a mass of 0.286/0.004036

= 70.8 g / mol

Therefore the molar mass of the gas is 71 g/mol (2 sfg)