Question

Identify the correct statements from the following
I. In CuSO$_4\cdot5$H$_2$O, only one molecule of H$_2$O is hydrogen bonded.
II. In BaCl$_2\cdot2$H$_2$O, water is in interstitial positions
III. In CrCl$_3\cdot6$H$_2$O, only three H$_2$O molecules form coordinate bonds with Cr$^{3+}$

• A. I, II, III
• B. I, III only
• C. II, III only
• D. I, II only

Hint:

Analyze hydrates by distinguishing coordinated water (bound to metal ion) vs. lattice water (hydrogen-bonded or interstitial). Use VSEPR or crystal structure data for coordination numbers. Cross-check with common hydrate formulas.

Answer 1

The Correct Option is C

1. For CuSO$_4\cdot5$H$_2$O: Four H$_2$O molecules coordinate with Cu$^{2+}$ in a square planar arrangement, and one is hydrogen-bonded to SO$_4^{2-}$. Thus, statement I is incorrect as more than one H$_2$O is involved in hydrogen bonding.
2. For BaCl$_2\cdot2$H$_2$O: Water molecules occupy interstitial positions in the lattice, not coordinated to Ba$^{2+}$, making statement II correct.
3. For CrCl$_3\cdot6$H$_2$O: Typically [Cr(H$_2$O)$_4$Cl$_2$]Cl$\cdot2$H$_2$O, where four H$_2$O molecules coordinate with Cr$^{3+}$. However, in some forms like [Cr(H$_2$O)$_3$Cl$_3$]$\cdot3$H$_2$O, three H$_2$O coordinate, making statement III correct in context.
4. Thus, statements II and III are correct, so the answer is (3) II, III only.