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NCERT Class XII Chemistry
Chapter - The Solid State
Questions with Solutions

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Question : 25
Total: 50
If NaCl is doped with 10‌–3 mol % SrCl‌2, what is the concentration of cation vacancies ?
Solution:  
Let moles of NaCl = 100
∴ Moles of SrCl‌2 doped = 10‌–3
Each Sr‌2+ will replace two Na‌+ions. To maintain electrical neutrality it occupies one position and thus creates one cation vacancy.
∴ Moles of cation vacancy in 100 moles NaCl = 10‌–3
Moles of cation vacancy in one mole NaCl = 10‌–3 × 10‌–2 = 10‌–5
∴ Number of cation vacancies = 10‌–5× 6.022 × 10‌23 = 6.022 × 10‌18 mol‌–1
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