Pre-lab Questions 1. An unknown gas reacts with silane gas (SiH) to produce a so

Question

Pre-lab Questions 1. An unknown gas reacts with silane gas (SiH) to produce a solid product. Using an experiment similar to the one performed in this lab, a sample of silane was placed at one end of a glass tube and the unknown at the other end. After 3 minutes, 33 seconds the solid form ned in tube, 29.4 cm from the silane end of the tube and 20.6cm from the end with the unknown. a) Calculate the rate of diffusion of silane (in cm/s). b) Calculate the rate of diffusion of the unknown (in cm/s) c) Calculate the molar mass of the unknown gas.

Explanation / Answer

Total time = 3 min 33 sec = 3X60 + 33 = 213 sec
a) rate of diffusion of silane =distance / time

=29.4 cm / 213 sec

= 0.138 cm/s

b) Similarly, rate of diffusion of unknown = 20.6 cm / 213 s = 0.096cm /s

c) using graham law of diffusion,

Rate of diffusion of silane / rate of diffusion of unknown

= ? (molar mass of unknown / molar mass of silane )

On rearranging, we get

Molar mass of unknown = ( rate of diffusion of silane / rate of diffusion of unknown)^2 * molar mass of silane

= ( 0.138 / 0.096)^2 * 32.117 g mol-1

= 66.3 g mol-1

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