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Question
An unknown gas shows a density of 3 g per litre at 273°C and 1140 mm Hg pressure. What is the gram molecular mass of this gas?
Solution
Given:
P1 = 1140 P2 = 760 mm
V1 = 1000 cc V2 = ?
T1 = 273 + 273 = 546 k T2 = 273 k
`("P"_1"V"_1)/"T"_1 = ("P"_2"V"_2)/"T"_2`
V2 = `("P"_1"V"_1"T"_2)/("T"_1"P"_2)`
= `(273 xx 1140 xx 1000)/(546 xx 760)`
∴ V2 = 750 cc
750 cc at STP weighs = 2.4 g
∴ 224000 cc at STP weighs = `(2.4 xx 22400)/750`
= 71.68 g
∴ Mol. mass of gas = 71.68 g
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