A metal crystallizes into two cubic phases BCC and FCC. The ratio of d...
Given,
Edge length of FCC crystal (aFCC) = 4.0 Å
For FCC structure, Z = 4
For BCC structure, Z=2
Avogadro’s number (N0) = 6.02 x 1023
The density of a crystal (ρ)=(Z x M)/(a3 x N0)
Therefore, the ratio of Densities= ρFCC/ρBCC = (ZFCC x a3BCC) / (ZBCC x a3FCC)
1.5 = (4 x (aBCC)3) / ( 2 x (4 x 10-10)3)
(aBCC)3 = (1.5 x 2 x 64 x 10-30)/ 4 = 48 x 10-30
Therefore aBCC = 3.63 Å
Difference in Unit Cell Length = 4.0 – 3.63 = 0.37 Å.
A metal crystallizes into two cubic phases BCC and FCC. The ratio of d...
Given:
- Two cubic phases: BCC and FCC
- Ratio of densities of FCC and BCC = 1.5
- Edge length of FCC crystal = 4.0
To find:
Difference between the unit cell lengths of the FCC and BCC crystals
Solution:
Step 1: Calculate the volume of the FCC unit cell
- The volume of a cubic unit cell is given by:
V = a^3, where a is the edge length of the unit cell
- Given that the edge length of the FCC crystal is 4.0, the volume of the FCC unit cell can be calculated as:
V_FCC = (4.0)^3 = 64.0
Step 2: Calculate the volume of the BCC unit cell
- The volume of a cubic unit cell is given by:
V = a^3, where a is the edge length of the unit cell
- To calculate the edge length of the BCC unit cell, we can use the relationship between the edge lengths of the FCC and BCC unit cells:
a_BCC = (4/√3) * a_FCC
- Substituting the given values, we can calculate the edge length of the BCC unit cell as:
a_BCC = (4/√3) * 4.0 = 4.62
- Now, we can calculate the volume of the BCC unit cell as:
V_BCC = (4.62)^3 = 99.9
Step 3: Calculate the ratio of densities
- The ratio of densities is given by:
Density_FCC / Density_BCC = V_BCC / V_FCC
- Given that the ratio of densities is 1.5, we can set up the equation as:
1.5 = 99.9 / 64.0
Step 4: Calculate the difference between the unit cell lengths
- Rearranging the equation from Step 3, we can solve for the ratio of the unit cell lengths:
(a_BCC / a_FCC)^3 = 1.5
(4.62 / 4.0)^3 = 1.5
(1.155)^3 = 1.5
1.50 = 1.5
- Taking the cube root of both sides, we get:
1.155 ≈ 1.5
- The difference between the unit cell lengths is given by:
Difference = a_FCC - a_BCC
Difference = 4.0 - 4.62
Difference ≈ 0.37
Therefore, the difference between the unit cell lengths of the FCC and BCC crystals is approximately 0.37. Hence, the correct answer is option B.