Question

1)How many unit cells are present in a cube shaped ideal crystal of NaCl of mass 1gm?
2) If edge length of a KCl unit is 488pm ,what is the length of KCl bond if it crystalises in fcc structure?

Answer 1

Here is the answer for the first question. Kindly send the other question in a separate mail so that we can help you better.

1) As NaCl is a FCC lattice so the total number of molecules in the FCC lattice is 4.
One unit cell of NaCl contains 4 NaCl units (ie) has mass
⇒(4×58.5) / (6.023×10^23) g ( since the mass of NaCl molecule is 58.5 g/mol )
No. of unit cell in 1g =(6.02×10^23) / (4×58.5)
⇒2.57×10^21