37.7mL vol. of unknown gas collected over H2O at 19 deg.celsius and total pressure of 770 torr.Mass gas 68.6mg.

What is the pressure of the"dry"unknown gas?

What volume does gas occupy?

How many moles gas are collected?

What is the molar mass of the gas?

vapour pressure of water at 19 degree C = 16.418 torr. So pressure of dry gas = total pressure - pressure of water vapour

770 - 16.418 = 753.582 torr.

Volume occupied = 37.7 ml = 0.0377 L

Temperature = 19 degree C = 273 + 19 = 292 K

pressure = 753.582 torr = 0.99 atm

Now we will use ideal gas equation to find the moles.

PV = nRT

Where P is pressure, V is volume, n is the number of moles, R is universal gas constant and T is temperature.

R = 0.0821

n = PV/ RT= (0.99 x 0.0377) / (0.0821 x 292) = 0.0015568 moles.

Mass of the gas = 68.6 mg = 0.0686 g

Moles = mass / molar mass

molar mass = mass/ moles = 0.0686 / 0.0015568= 44.0647 g.

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