Question

The incorrect statement is :

• A. $Cu^{2+}$ salts give red coloured borax bead test in reducing flame
• B. $Cu^{2+}$ and $Ni^{2+}$ ions give black precipitate with $H_2S$ in presence of $HCl$ solution
• C. Ferric ion gives blood red colour with potassium thiocyanate
• D. $Cu^{2+}$ ion gives chocolate coloured precipitate with potassium ferrocyanide solution

Answer 1

The Correct Option is B

To determine which statement is incorrect, let's analyze each option based on chemical reactions and principles:

1. Cu^{2+} salts give red coloured borax bead test in reducing flame:

   In the borax bead test, Cu^{2+} ions typically produce a green bead in oxidizing flame and a reddish one if conditions favor reduction. Therefore, this statement can be considered correct under specific conditions. However, for standard tests, it's not the usual representation.

2. Cu^{2+} and Ni^{2+} ions give black precipitate with H_2S in presence of HCl solution:

   In acidic conditions with HCl, H_2S does not precipitate these ions. Cu^{2+} and Ni^{2+} require alkaline conditions to form their respective sulfides. Therefore, this statement is incorrect.

3. Ferric ion gives blood red colour with potassium thiocyanate:

   Ferric ions react with potassium thiocyanate to form a complex that gives a characteristic blood-red color. This statement is correct.

4. Cu^{2+} ion gives chocolate coloured precipitate with potassium ferrocyanide solution:

   When Cu^{2+} ions react with potassium ferrocyanide, a chocolate brown precipitate of copper(II) ferrocyanide is formed. This statement is correct.

After reviewing the options, the incorrect statement is that Cu^{2+} and Ni^{2+} ions give black precipitate with H_2S in presence of HCl solution, because these ions need an alkaline environment to form sulfides.