Question

If NaCl is doped with 10^-3 mol % of SrCl₂ , what is the concentration of cation vacancies?

Answer 1

Every Sr²⁺ ion causes one cation vacancy (because two Na⁺ ions are replaced by one Sr²⁺ and it occupies the site of one Na⁺ ion and the other site remains vacant.) 

Therefore, introduction of 10^-3 moles of SrCl₂ per 100 moles of NaCl would introduce 10^-3 moles cation vacancies in 100 moles of NaCl.

No. of vacancies per mole of NaCl 

= \(\frac{10^{-3}}{100}\times\) 6.02 × 10²³ 

= 6.02 × 10¹⁸