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 = \(\frac{10^{-3}}{100}\times6.02\times10^{23}\)

= 6.02 × 10¹⁸