Complexes [Ag(CN)₂]⁻ and [Au(CN)₂]⁻ enable smoother and more even electroplating of silver and gold than simple metal ions. In black and white photography, the developed film is fixed by washing with hypo solution, forming the complex ion [Ag(S₂O₃)₂]³⁻ that dissolves undecomposed AgBr.
Explain the significance of using complexes like [Ag(CN)₂]⁻ and [Au(CN)₂]⁻ in electroplating silver and gold, and how is black and white photography fixed using coordination compounds?
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[Ag(CN)₂]⁻ and [Au(CN)₂]⁻ complexes are crucial in electroplating due to their stability and ability to provide metal cations for reduction. In silver electroplating, [Ag(CN)₂]⁻ is reduced to deposit a thin layer of silver on a substrate. Similarly, [Au(CN)₂]⁻ is used for gold electroplating. In black and white photography, coordination compounds play a role in fixing the image. After exposing a photosensitive film to light, unexposed silver halide grains are removed. The remaining silver halides are reduced to elemental silver by a developing agent, forming the black areas of the image. Coordination compounds like sodium thiosulfate then fix the image by solubilizing unexposed silver halides, preventing further development.