Concept explainers
Interpretation:
The density of a hypothetical ionic compound for given radii and masses of cations and anions, is to be determined.
Concept introduction:
Ionic compounds contain cations and anions that are arranged in a crystal lattice.
A crystal lattice is made of small repeating unit cells.
A unit cell is of primitive or centered type.
Each atom or ion in a unit cell is shared by the adjacent cells. An atom or ions at corners is shared by eight unit cells.
The edge length of a body-centered cubic cell is given by the relation as follows:
Here,
is the edge length,
is the radius of cation, and
The volume of the unit cell
The density
Here,
is the mass.
Answer to Problem 146AP
Solution:
Explanation of Solution
Given information:
Radii of the anion
The figure is as shown below:
The given unit cell is body-centered, in which there is one cation at the center, and eight anions at the corners, shared by eight unit cells.
The contribution of 8 anions at the corners to one unit cell is:
In the unit cell, one anion and one cation are present.
The mass of an anion is
and that of a cation is
The relation between
and
is as:
Convert the mass to grams as follows:
Similarly,
Thus, the mass of the unit cell will be:
The formula to calculate the edge length is as:
Substitute
for
and
for
in the above expression as:
Convert the edge length to
as follows:
The expression to calculate volume is as:
Substitute
in the above expression as:
Now, finally calculate density as:
Substitute
for
for
in the above expression as:
The density of the hypothetical ionic compound is
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Chapter 11 Solutions
Looseleaf Study Guide For Chemistry
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