Chemistry MCQ Practice

The time taken for 30 cm³ of a gas C_xH_y to diffuse through a porous barrier was the same as that for 30 cm³ of nitrogen gas under the same conditions.

 

Determine the value of x and y.

 

A)  x = 1, y = 2

 

B)  x = 1, y = 4

 

C)  x = 2, y = 4

 

D)  x = 3, y = 6

 

 

Answer: C

 

- Recall: rate of diffusion of a gas is dependent on its mass.
- Since C_xH_y takes the same amount of time to diffuse as nitrogen gas, C_xH_y must have the same relative molecular mass as nitrogen gas i.e. 14x2 = 28.

 

Common mistake: students will put down the relative mass of nitrogen to be 14. Bear in mind that nitrogen exists as diatomic molecules i.e. N₂.