Hydrogen (H2) and helium (He) are mixed in a 20.0L flask at room temperature (20 â—¦C). The partial pressure of

Question

Hydrogen (H2) and helium (He) are mixed in a 20.0L flask at room temperature (20 ◦C). The partial pressure of hydrogen is 250 mmHg and that of helium is 75 mmHg. (a) How many grams of H 2 are present? (b) How many grams of He are present?

Answer 1

find moles:

Hydrogen:

PV=nRT

(250Torr)(20.0L) = n (62.36L-Torr/mol-K)(293K)

n = 0.2736 moles hydrogen

Helium:

PV=nRT

(75Torr)(20.0L) = n (62.36L-Torr/mol-K)(293K)

n = 0.08210 moles helium

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find grams

0.2736 moles H2 @ 2.0159 g / mol = 0.55154 g H2

0.08210 g He @ 4.0026 g/mol = 0.3286 g He

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your answers: 0.55 g H2  & 0.33 g He