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# Solution for At 0°C, the Density of a Certain Oxide of a Gas at 2 Bar is Same as that of Dinitrogen at 5 Bar. What is the Molecular Mass of the Oxide? - CBSE (Science) Class 11 - Chemistry

ConceptLaws of Chemical Combination Avogadro Law

#### Question

At 0°C, the density of a certain oxide of a gas at 2 bar is same as that of dinitrogen at 5 bar. What is the molecular mass of the oxide?

#### Solution 1

Density (d) of the substance at temperature (T) can be given by the expression,

d = "Mp"/"RT"

Now, density of oxide (d1) is given by,

d_1 = (M_1p_1)/"RT"

Where, M1 and p1 are the mass and pressure of the oxide respectively.

Density of dinitrogen gas (d2) is given by,

d_2 = (M_2p_2)/"RT"

Where, M2 and p2 are the mass and pressure of the oxide respectively.

According to the given question,

d_1 = d_2

:. M_1p_1 = M_2p_2

Given

p_1 =  "2bar'

p_2 = "5 bar"

Molecular mass of nitrogen, M2 = 28 g/mol

Now M_1 = (M_2p_2)/p_1

= (28xx5)/2`

= 70 g/mol

Hence, the molecular mass of the oxide is 70 g/mol.

#### Solution 2

Using the expression, d =MP/RT , at the same temperature and for same density,

M1P1 = M2P2 (as R is constant)
(Gaseous oxide) (N2)

or

M1 x 2 = 28 x 5(Molecular mass of N2 = 28 u)
or M1 = 70u

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Solution At 0°C, the Density of a Certain Oxide of a Gas at 2 Bar is Same as that of Dinitrogen at 5 Bar. What is the Molecular Mass of the Oxide? Concept: Laws of Chemical Combination - Avogadro Law.
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