Question

Determine the number of moles of each unknown & calculate each of their masses in g/mol.

The mask of the original flask was 51.11g, and 2ml of unknown was used. The trials state the temperature the at which the unknown effused completely out of the flask and what the new mass the flask was.

P=.980 atm

Trial 1 - Temp: 90 C, Mass: 54.35g

Trial 2 - Temp: 92 C, Mass: 54.41g

Please help!! will rate!!

Answer 1

We use the following to determine the molar mass of the gas.
PV = nRT ........... ideal gas equation
PV = mRT / M ... n = m/M..... m=mass, M=molar mass
M = mRT / PV ... solve for M

P = 0.980 atm ,volume V = 2.0 ml

trial 1.mass of unknown used = 54.35 g - 51.11 g = 3.24 g

trial 2. mass of unknown used = 54.41 g - 51.11 g = 3.3 g

M = mRT / PV

M1 = 3.24 g x 0.082 x (90+273) / 0.98 x 0.002 L

M1 = 48597.55 g/mol

M2 = 3.3 x 0.082 x 365 / 0.98 x 0.002 L = 50392.34 g/mol

M = (M1 + M2) / 2 = 49494.94 g/mol

moles of unknown = 3.27 g /  49494.94 g/mol = 6.6x10^-5 moles