CBSE Class 12 · 2017 · d and f Block ElementsLong Answer

WhatsApp Email

(a) The following are transition metal ions of the 3d series:
Ti⁴⁺, V²⁺, Mn³⁺, Cr³⁺
(Atomic numbers: Ti = 22, V = 23, Mn = 25, Cr = 24)
Answer the following:
i) Which ion is most stable in aqueous solution, and why?
ii) Which ion is a strong oxidising agent, and why?
iii) Which ion is colourless, and why?
(b) Complete the following equations:
i) 2MnO₄⁻ + 16H⁺ + 5S²⁻ →
ii) KMnO₄ —heat→

Solution

(a)(i) Cr

^{3 +}

(3d

^{3}

): the exactly half-filled t

_{2 g}^{3}

set gives it special stability in water.
(ii) Mn

^{3 +}

(3d

^{4}

): gaining one electron yields the extra-stable half-filled 3d

^{5}

(Mn

^{2 +}

), so Mn

^{3 +}

is strongly oxidising.
(iii) Ti

^{4 +}

(3d

^{0}

): with no d electrons there are no d–d transitions, so it is colourless.
(b)(i) Acidified permanganate oxidises sulphide to sulphur:

2Mn O_{4}^{-} + 16 H^{+} + 5 S^{2 -} \to 2M n^{2 +} + 5S ↓ + 8 H_{2} O

(ii)

2KMn O_{4} Δ K_{2} Mn O_{4} + Mn O_{2} + O_{2}

CBSE Class 12 Board · 2017 · Subjective

Practise more: all CBSE board PYQs on d and f Block Elements →

CBSE Class 12 · 2017 · d and f Block ElementsLong Answer

Solution

More board questions on d and f Block Elements