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KF has NaCl structure. What is the distance (in pm) between K+ and F- in KF. If density is 2.48 gm/cm3?

Option: 1

268.8


Option: 2

537.5


Option: 3

155.3


Option: 4

5.375


Answers (1)

best_answer

Density formula : 

d=\frac{Z\times M}{a^3\times N_A}

For NaCl structure Z = 4

M for KF=58 

2.48=\frac{4\times 58}{a^3\times 6.02 \times 10^{23}}

a^3=\frac{4\times 58}{2.48\times 6.02 \times 10^{23}}=150\times 10^{-24}

a=537.5pm

Rock salt structure or NaCl type structure -

Cl^-   located at all corners and face centre

Na^+ located at all octahedral voids

Edge length =2(r_{Na^+}+r_{Cl^-})

Coordination number = 6:6
Thus, the distance between K+ and F- is \frac{a}{2}=268.8pm   
 
 

Posted by

Shailly goel

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