Question

Which of the following statement(s) is/are correct?

• A. Articles can be electroplated with silver and gold much more smoothly and evenly from solutions of complexes, $[Ag(CN)_2]^-$ and $[Au(CN)_2]^-$ than from a solution of simple metal ions.
• B. In black and white photography, hypo solution is used to dissolve undecomposed AgBr to form a complex ion $[Ag(S_2O_3)_2]^{3-}$.
• C. EDTA is used in treatment of lead poisoning.
• D. Hardness of water is estimated by use of $Na_2[EDTA]$ as it does not react with $Mg^{2+}$ ion.

Answer 1

Answer: (A), (B), (C)

A, B, and C

Answer 2

• A. Electroplating smoothness is enhanced by a low concentration of free metal ions. Cyanide complexes, $[Ag(CN)_2]^-$ and $[Au(CN)_2]^-$, maintain low concentrations of free $Ag^+$ and $Au^+$ ions due to their high stability, enabling smoother and more even deposition compared to simple salt solutions.
• B. In black and white photography, sodium thiosulfate (hypo) acts as a fixing agent. It dissolves unexposed silver bromide (AgBr) by forming the soluble complex $[Ag(S_2O_3)_2]^{3-}$, which is then washed away.
• C. EDTA is a chelating agent. It is used in the treatment of lead poisoning by binding to lead ions ($Pb^{2+}$) to form a stable, soluble complex, $[Pb(EDTA)]^{2-}$, facilitating its excretion from the body.
• D. The hardness of water is estimated by titrating with EDTA, as it forms stable complexes with both $Ca^{2+}$ and $Mg^{2+}$ ions (e.g., $[Ca(EDTA)]^{2-}$ and $[Mg(EDTA)]^{2-}$). The statement that EDTA does not react with $Mg^{2+}$ is incorrect.