A250 ml flask contains he at a pressure of 700 torr and a temperature of 25 degrees c. what is the mass of he present?

0.038 g He

From the question we are given;

Volume of the flask, V = 250 mL

Pressure of He, P = 700 torr

Temperature, T = 25°C, but K = 273 + °C

                         = 298 K

We are required to calculate the mass of Helium present in the flask.

We are going to use the ideal gas equation to first get the number of moles of He present in the flask.

Ideal gas equation, PV = nRT, where n is the number of moles and R is the ideal gas constant.

In this case, R will be 62.364 L.Torr/mol.K, since the pressure is in torr.

Rearranging the equation;

n = PV ÷ RT

  = (0.25 L × 700 torr) ÷ (62.364 × 298 K)

  = 0.00942 moles

With the number of moles, we can calculate the mass of He.

Mass = Number of moles × molar mass

Molar mass of He = 4.0 g/mol

Therefore,

Mass = 0.00942 moles × 4.0 g/mol

         = 0.03768 g

         = 0.038 g He

tracks, burrows, eggshells, nests, tooth marks, or gastroliths

the answer is definitely c.