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  • Give answer! KF has NaCl structure. What is the distance between K+ and F- in KF . If density is 2.48 gm/cm3 ?

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

  • Option 1)

    268.8 pm

  • Option 2)

    537.5 pm

  • Option 3)

    155.3 pm

  • Option 4)

    5.375 pm

 

Answers (1)

best_answer

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}=15\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

- wherein

Total number of Cl^{-} = 4

Total number of Na^{+} = 4

Total number of NaCl molecule per unit cell = 4

Ex : halides of  K^{+} , Na^{+} , Rb^{+} and FeO

 

 

\frac{a}{2}=268.8pm


Option 1)

268.8 pm

This is correct

Option 2)

537.5 pm

This is incorrect

Option 3)

155.3 pm

This is incorrect

Option 4)

5.375 pm

This is incorrect

Posted by

Aadil

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