A chemical reaction, A(s) rightarrow B(s) + C(g) occurs when substance A is stro

Question

A chemical reaction, A(s) rightarrow B(s) + C(g) occurs when substance A is strongly heated. The molecular mass of the gaseous product was to be determined from the following experimental data. Mass of A: 4.962 g ; Mass of residue (B) after cooling and weighing when no more gas was evolved: 3.684 g. When collected and stored in a 658.5 mL glass vessel at 30.4 degree C, the gas exerted a pressure of 748.5 torr. From this data, determine the apparent molecular mass of C, assuming it behaves as an ideal gas. 6.54 g mol^-1 47.5 g mol^-1 49.1 g mol^-1 71.6 g mol^-1 141. g mol^-1

Explanation / Answer

Given,

Mass of A = 4.962 g

Mass of B = 3.684 g

Since Mass is conserved.

Mass of A = Mass of B + Mass of C

=> Mass of C = 4.962 - 3.684 = 1.278 g

Volume of Glass Vessel = 658.5 mL = 0.6585 L

Temp. = 30.4 degree C = 303.4 K

Pressure = 748.5 torr = 748.5 / 760 = 0.985 atm

R = gas constant = 0.0821

Using,

PV = nRT

=> 0.985 x 0.6585 = n x 0.0821 x 303.4

=> n = Number of moles of C = 0.026 moles

Mass = 1.278 g

Molar Mass = Mass / Moles = 1.278 / 0.026 = 49.1 g / mol

C) 49.1 g / mol

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