In a cylindrical water tube of length 4 cm and radius 6 mm, at t=0 s, the concentration of
mole
molecules of oxygen changes from 0.5
m3
mole
to 0.1
across the tube.
If the diffusion constant of oxygen inside water
is 8x 10-10 m2
find:
S
The number of mole of oxygen going from the
higher concentration to the lower concentration
every second
n =
v mole

Uranium has two naturally occurring isotopes. 238u has a natural abundance of 99.3% and 235u has an abundance of 0.7%. it is the rarer 235u that is needed for nuclear reactors. the isotopes are separated by forming uranium hexafluoride uf6, which is a gas, then allowing it to diffuse through a series of porous membranes. 235uf6 has a slightly larger rms speed than 238uf6 and diffuses slightly faster. many repetitions of this procedure gradually separate the two isotopes. what is the ratio of the rms speed of 235uf6 to that of 238uf6? express your answer to five significant figures.