Question

$NH _4 SCN$ can be used to test one or more out of $Fe ^{3+}, Co ^{2+}, Cu ^{2+}$

• A. $Fe ^{3+}$ only
• B. $Co ^{2+}, Cu ^{2+}$
• C. $Fe ^{3+}, Cu ^{2+}$
• D. All of these

Answer 1

Answer: (D)

$Cu ^{2+}+2 SCN ^{-} \rightarrow \underset{\text{black}}{Cu ( SCN )_2} \downarrow \xrightarrow{\Delta} \underset{\text{black white}}{CuSCN} \downarrow+( SCN )_2$
$Fe ^{3+}+ SCN ^{-} \rightarrow \underset{\text{red}}{[ Fe ( SCN )]^{2+}}$
$Co ^{2+}+ SCN ^{-} \rightarrow \underset{\text{blue}}{\left[ Co ( SCN )_4\right]^{2-}}$