Question #d708e

1 Answer
Ernest Z.
Jul 5, 2014

The balloon contains 0.31 g of helium.

This is an ideal gas law problem.

http://socratic.org/questions/what-is-the-ideal-gas-law-1

We can use the Ideal Gas Law to calculate the moles of helium. From that, you can calculate the mass of helium.

In your problem,

#P# = 735 mmHg x #(1"atm")/(760"mmHg")# = 0.967 atm
#V# = 2.0 L
#T# = (30.0 + 273.15) K = 303.2 K

#PV = nRT#

#n = (PV)/(RT) = (0.967"atm" × 2.0"L")/(0.082 06"L·atm·K⁻¹mol⁻¹" × 303.2"K")# = 0.0777 mol

Mass = 0.0777 mol He × #(4.003"g He")/(1"mol He")# = 0.31 g He

Note: The answer can have only two significant figures, because that is all you gave for the volume of the balloon. If you need more precision, you will have to recalculate.

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