Calculate the value of Avogadro's number from the following data : Density of NaCl = 2.165 g cm⁻³, Distance between Na⁺ and Cl⁻ ions in NaCl crystal = 281 pm.
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According to the formula
d=(Z* M)/ NA*V where d= density, Z= no. of atoms per unit cell which in case of NaCl will be 4, M= mol. mass, NA= Value of Avogadro no., V= Volume, the answer to your question can be easily calculated.
Firstly remember for NaCl lattice,
a=2(r+ + r−)
= 2( 281)
= 562 pm
also, Mol. mass for NaCl will be 58.5
then,
d= (Z *M) / NA * V ... { Note, V (volume) = a³)
2.165= 4 * 58.5 / NA * (562 * 10^-10)³
You'll get NA= 6.02 * 10^23
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