25. If NaCl is doped with 10−3 mol % of SrCl2, what is the concentration of cation vacancies? 


It is given that NaCl is doped with 10−3 mol % of SrCl2.
This means that 100 mol of NaCl is doped with 10−3 mol of SrCl2.
Therefore, 1 mol of NaCl is doped with 10-3100 mol of SrCl= 10−5 mol of SrCl2
Cation vacancies produced by one Sr2+ ion = 1
The concentration of the cation vacancies
produced by 10-5 mol of Sr2+ ions=10-5×6.022×1023=6.022×1018 mol-1
Hence, the concentration of cation vacancies created by SrCl2 is 6.022 × 108 per mol of NaCl.