Question

Which of these is the correct group reagent for group cations?

• A. $M{n}^{2+}$ $C{o}^{2+}$ $Z{n}^{2+}$ $N{i}^{2+}$; $dil.HCl$
• B. $M{n}^{2+}$ $C{o}^{2+}$ $Z{n}^{2+}$ $N{i}^{2+}$; $N{H}_{4}Cl+N{H}_{4}OH+H_{2}S$
• C. $M{n}^{2+}$ $C{o}^{2+}$ $Z{n}^{2+}$ $N{i}^{2+}$; $N{H}_{4}Cl+N{H}_{4}OH$
• D. $M{n}^{2+}$ $C{o}^{2+}$ $Z{n}^{2+}$ $N{i}^{2+}$; $HCl+H_{2}S$

Answer 1

The correct option is B $M{n}^{2+}$ $C{o}^{2+}$ $Z{n}^{2+}$ $N{i}^{2+}$; $N{H}_{4}Cl+N{H}_{4}OH+H_{2}S$

The group reagent for $M{n}^{2+},C{o}^{2+},Z{n}^{2+},N{i}^{2+}$ is $N{H}_{4}Cl+N{H}_{4}OH+H_{2}S$ as this belongs to fourth group

The fourth group of cations include $M{n}^{2+},C{o}^{2+},Z{n}^{2+},N{i}^{2+}$.

Of these, Zinc salts are colourless, Manganese salts are faint pink or colourless, and Nickel and cobalt salts may be brightly coloured, often blue-green.

The precipitate, washed in water is reacted with extremely dilute hydrochloric acid. This precipitates nickel salts if any.

The supernatant liquid is filtered and reacted with an excess of Sodium Hydroxide. This precipitates any Manganese salts.

Hydrogen sulphide is passed through the supernatant liquid. If a white precipitate forms, Zinc is present.