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The density of KBr is 2.75g cm^(-3). The...

The density of KBr is 2.75g `cm^(-3)`. The length of the edge of the unit cell is 654 pm. Show that KBr has a face centred cubic structure.(`N_A=6.023xx10^(23) mol^(-)` at. mass : K=39, Br = 80]

A

The unit cell is fcc.

B

`Z = 4`.

C

There are four `"constituents"//"unit"` cells.

D

There are `8` ions at corners and `6` at the centres of the faces.

Text Solution

Verified by Experts

The correct Answer is:
A, B, C, D
`Z_(eff) = (rho xx a^(3) xx 10^(-30) xx N_(A))/(Mw)`
`= (2.75 xx (654)^(3) xx 10^(-30) xx 6 xx 10^(23))/(119) = 4`
`Z_(eff) = 4`, suggest fcc sturcture.
Thus, there are four `KBr` units. There are `8` ions at the corner and `6` at the face centres.
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