A 2.00 liter evacuated container has a mass of 1050.0 g. When the container is filled with an unknown gas at 800. mm Hg pressure and 25.0 °C the mass is 1052.4 g. What is the molar mass of the gas (in g-mol"')? (A) 28
(B) 31
(C) 54
(D) 56

(A) 28

Explanation:

To solve this problem we use the PV=nRT equation, where:

We input the data:

And solve for n:

Now we calculate the gas' mass:

Finally we calculate the unknown gas' molar mass, using its mass and its number of moles:

So the answer is option (A).

nacl is added to the aqueous of what? ? in order to get a proper answer you have to specify the exact composition of the aqueous solution.