Question

Yellow compound of lead chromate gets dissolved on treatment with hot NaOH solution. The product of lead formed is a:

• A. Tetraanionic complex with coordination number six
• B. Neutral complex with coordination number four
• C. Dianionic complex with coordination number six
• D. Dianionic complex with coordination number four

Answer 1

The Correct Option is D

The given question involves the dissolution of a yellow compound of lead chromate in a hot NaOH solution, forming a lead complex. We'll solve the question step-by-step to identify the correct product. 

Lead chromate (\( \text{PbCrO}_4 \)) is a yellow compound commonly used in paints and pigments. When treated with a hot sodium hydroxide (\( \text{NaOH} \)) solution, it reacts to form a lead complex. The possible options indicate different types of complexes.

Let's analyze the reaction:

1. \(PbCrO_4\) when dissolved in \(NaOH\), forms \(Pb(OH)_4^{2-}\), which is a lead complex.
2. In this complex, the lead ion (\( \text{Pb}^{2+} \)) coordinates with hydroxide ions (\( \text{OH}^- \)) to form \(Pb(OH)_4^{2-}\).
3. This complex is dianionic because it carries a -2 charge.
4. The lead atom is coordinated by four hydroxide ions, giving it a coordination number of four.

At this point, comparing the identified complex \(Pb(OH)_4^{2-}\) with the options given:

• The first option, "Tetraanionic complex with coordination number six," is incorrect since the lead complex formed is dianionic, not tetraanionic, and has a coordination number of four, not six.
• The second option, "Neutral complex with coordination number four," is incorrect because the complex is not neutral; it has a charge of -2.
• The fourth option, "Dianionic complex with coordination number four," is correct as it accurately describes the characteristics of the complex \(Pb(OH)_4^{2-}\).
• The third option, "Dianionic complex with coordination number six," is incorrect because the coordination number is four, not six.

Therefore, the correct answer is: Dianionic complex with coordination number four.

This explanation shows how basic coordination chemistry and complex ion formation principles are applied to solve the problem.

Answer 2

The reaction of lead chromate with NaOH (in hot, excess conditions) results in the formation of a soluble dianionic complex:

PbCrO₄ + NaOH (hot, excess) → [Pb(OH)₄]^2- + Na₂CrO₄

The product [Pb(OH)₄]^2- is a dianionic complex with a coordination number of four.