Question

A sample of helium gas has a volume of 2.75 L at STP. How many grams of He are present?

Answer 1

Molar mass He = 4.0 g/mol

1 mole --------- 22.4 L ( at STP )
? mole ---------- 2.75 L

2.75 x 1 / 22.4 => 0.1227 moles

1 mole He ------------ 4.0 g
0.1227 moles --------- ?

0.1227 x 4.0 / 1 => 0.4908 g of He

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