# KF has NaCl structure. What is the distance between K+ and F– in KF if density is 2.48 g cm-3?

**KF has NaCl structure. What is the distance between K ^{+} and F^{–} in KF if density is 2.48 gm cm^{-3 }?**

**Answer:**

**Given Values**

Density = 2.48 gm/cm^{3}

Formula mass (M) = KF = 39+19=58

KF has NaCl structure : Means, KF has FCC unit cell. So, Z = 4

Avogadro Number (N_{A}) = 6.02 × 10^{23}

Formula used : \( D=\frac{Z \times M}{\left ( a \right )^{3}\times N_{A}} \)

**Calculations**

\( \left ( a \right )^{3}=\frac{Z \times M}{D \times N_{A}} \)

\( \left ( a \right )^{3}=\frac{4 \times 58}{2.48 \times 6.02 \times 10^{23}} \) = 155.4 × 10^{-24} cm^{3}

a = 5.38 × 10^{-8} cm = 538 pm

\( d = \frac{a}{2} = \frac{358~pm}{2} = 269~pm \)

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