Qualitative Analysis - Result Question 30
####30. Which of the following statement(s) is (are) correct with reference to the ferrous and ferric ions?
$(1998,2 M)$
(a) $Fe^{3+}$ gives brown colour with potassium ferricyanide
(b) $Fe^{2+}$ gives blue precipitate with potassium ferricyanide
(c) $Fe^{3+}$ gives red colour with potassium thiocyanate
(d) $Fe^{2+}$ gives brown colour with ammonium thiocyanate
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Answer:
Correct Answer: 30. $(c)$
Solution:
- The blue precipitate of $Fe^{2+}$ ion with potassium ferricyanide is due to formation of Turnbull’s blue $KFe\left[Fe(CN) _6\right]$.
$$ Fe^{2+}+K _3\left[Fe(CN) _6\right] \longrightarrow KFe\left[Fe(CN) _6\right]+2 K^{+} $$
The red colour of $Fe^{3+}$ ion with potassium thiocyanate is due to formation of $\left[Fe(SCN) _3\right]$.
$$ Fe^{3+}+3 KSCN \longrightarrow \underset{\text { Red coloured }}{\left[Fe(SCN) _3\right]+3 K^{+}} $$
