Question

"Photo- gray" lenses for eyeglasses darken in bright sunshine because lenses contain tiny, transparent AgCl crystals. Exposures to light removes electrons from Cl^- ions, forming a chlorine atom in an excited state (indicated below by the asterisk): Cl^- -->hn Cl* + e^-

The electrons are transferred to Ag^+ + e^- ---> Ag

Silver metal is reflective, producing the photo gray color. How might substituation of AgBr for AgCl affect the light sensitivity of photo-gray lenses? In answering this question, consider whether more or less energy is needed to remove an electron from a Br^- ion than from a Cl^- ion.

Answer 1

Answer – We are given the Photo- gray lenses for eyeglasses darken in bright sunshine because lenses contain tiny, transparent AgCl crystals. This is happening due to the light removes electrons from Cl^- ions, forming a chlorine atom in an excited state and this electron take by silver ion and form the Ag. This silver metal is reflective, producing the photo gray color.

When we substitution of AgBr for AgCl, then it required less the light sensitivity of photo-gray lenses. In the very low sunshine also the "Photo- gray" lenses for eyeglasses darken, because the for the Br required very less energy for the removing the electron than Cl due to less electronegativity and larger size than Cl. So Br can easily loss the electrons at low energy and it is not required more bright sunshine.

So the light sensitivity of photo-gray lenses increases more when we substitution of AgBr for AgCl.