Question

Question: What effect will the (unavoidable) presence of Schottky defects have on the determination of Avogadro’s number via the method described in problems 15 and 16?

Short answer

Answer:

The presence of Schottky defects has a little increase in the value determination of Avogadro’s number via the expected method.

Step-by-step solution

Schottky defect.

It is a form of point defect formed after the movement of both the cation and anion from its original position takes place completely out from the crystal.

The measured density of the crystal.

As per problems 15 and 16;

$density=\frac{z\times M}{volume\times N_A}$

Therefore,

$N_A=\frac{z\times M}{volume\times density}$

Here, M is the molecular weight, z is the number of atoms per unit cell and is the Avogadro’s number.

When the ion moves out from its place, occupying the interstitial site, the overall mass of the crystal decreases, and therefore, there is a significant decrease in the density.

Here, density and Avogadro’s number are inversely proportionalto each other.

Because of the decrease in density, the measured Avogadro’s number may be calculated as little more than the actual value.

And so Schottky defects cause a small bulging of the crystal and, therefore, a decrease in its density