Question

Using Evens method, calculate the magnetic moment of Cr(acac)3 if R0= -30, R= 516, Cbal=1.038, L= 2.5cm, m=.065g, and Xair and A are ignored. Hint: calculate Xg, then Xm, then Xa, then you will be able to calculate the magnetic moment.

Answer 1

The magnetic moment is determined from the magnetic susceptibility .

from the realtion of molar susceptibility of the paramagnetic atom and effective magnetic moment in Bohr Magnetons:

k = Boltzmann’s constant,

T = absolute temperature,

=Bohr Magneton,

N = Avogardo’s number

= susceptibility per gram of the paramagnetic ion
Thus, the equation simplifies to:

For calculation of

From the Evan's method gram susceptibility

L = sample height in centimeters= 2.5 cm

m = sample mass in grams= 0.065g
C = balance calibration constant = 1.038
R = reading from the digital display when the sample and tube is in place in the instrument = 516
R0 = reading from the digital display when the empty sample tube is in the instrument= -30
= volume susceptibility of air = to be ignored
A = cross-sectional area of the sample = to be ignored

Therefore

The molar susceptibility, is calculated by:

Chromium(III) acetylacetonate Formula weight = 350g/mol

Then formula for

For diamagnetic correction (from book)

Therefore

Then Effective magnetic moment =