The enthalpies of hydration of Ca²⁺, Mn²⁺ and Zn²⁺ follow the order · ABC26IN0458
Subject: Inorganic Chemistry · Chapter: Main Group Elements · Topic: Main Group Element – General · Exam: GATE 2005-2021 · Marks: 2 · Difficulty: Easy
The enthalpies of hydration of $\mathrm{Ca}^{2+}, \mathrm{Mn}^{2+}$ and $\mathrm{Zn}^{2+}$ follow the order
(a)$\mathrm{Mn}^{2+}>\mathrm{Ca}^{2+}>\mathrm{Zn}^{2+}$
(b)$\mathrm{Zn}^{2+}>\mathrm{Ca}^{2+}>\mathrm{Mn}^{2+}$
(c)$\mathrm{Mn}^{2+}>\mathrm{Zn}^{2+}>\mathrm{Ca}^{2+}$
(d)$\mathrm{Zn}^{2+}>\mathrm{Mn}^{2+}>\mathrm{Ca}^{2+}$
Answer
Answer: D ✓ checked by 4AB · confidence high
Explanation
Zn²⁺ (d¹⁰) and Mn²⁺ (high-spin d⁵) both have zero CFSE, so the hydration enthalpy is governed by ionic size / effective nuclear charge.
Radii: Zn²⁺ ≈ 74 pm < Mn²⁺ ≈ 83 pm < Ca²⁺ ≈ 100 pm; ΔH_hyd ≈ −2046, −1841 and −1577 kJ mol⁻¹ respectively.
Order of hydration enthalpy (magnitude): Zn²⁺ > Mn²⁺ > Ca²⁺ — option (d).
Study loop for Main Group Elements
· Browse this chapter in the app