Question

Brown ring test is used for identification of nitrate ion. Oxidation state of iron in the brown ring complex is X. Number of unpaired electrons in Brown ring complex is Y. Sum of X and Y is ________.

Answer 1

4

Answer 2

The brown ring test identifies nitrate ions ($NO_3^-$) using the complex $[Fe(H_2O)_5NO]^{2+}$. Let the oxidation state of iron be $x$. Since $H_2O$ is neutral and the nitrosonium ion ($NO^+$) has a charge of +1, the equation for the oxidation state of iron is $x + 5(0) + (+1) = +2$, which gives $x = +1$. Thus, X = 1. The electronic configuration of neutral iron (Fe, atomic number 26) is $[Ar] 3d^6 4s^2$. For $Fe^+$, it is $[Ar] 3d^7$. In the $3d^7$ configuration, there are 3 unpaired electrons according to Hund's rule ($\uparrow\downarrow \uparrow \uparrow \uparrow \uparrow$). Thus, Y = 3. The sum of X and Y is $1 + 3 = 4$.