chemistry question

Question

The density of KCl is 1.98 gcm-3

and the (110) reflection using palladium. radiation occurred at

8 degrees. What is the wavelength of the X-rays used?

Answer 1

Hi Tina K.,

Looks like KCl has a simple cubic lattice? You should look that up, but I THINK so. Then set up a diagram of the reflection from the (1 1 0) plane. First figure what the lattice spacing (1 0 0) is, using the molar mass of KCl and the stated density of crystal. (1 mole of KCl ions fill up (2*6.023^10^23)^(1/3) positions on any x or y or z axis.) Then figure what the spacing between (1 1 0) planes is, by comparison, using 3-D geometry -- it's quite simple, it's just a plane tilted towards you at a 45 degree angle. Use your diffraction knowledge then; for the particular radiation you MUST have a 1 lambda pathlength difference between the planes, towards that 8 degree angle. (So that they have constructive interference, right?) That will solve for lambda, directly.

-- Cheers, -- Mr. d.