A photography-restoration workshop produces a waste solution of silver nitrate after developing archive film negatives. To recover the silver rather than discard it, a technician suspends a coil of iron wire in a beaker of the waste silver nitrate solution overnight. (a) Describ…

Answer: ((a)) A grey/dark, metallic-looking deposit of silver forms on the surface of the iron wire; the colourless solution gradually turns very pale green, as iron(II) ions form. ((b)) Iron is more reactive than silver, so iron atoms have a greater tendency than silver to form positive ions. Iron atoms lose electrons (forming Fe^2+ ions), and these electrons are transferred to Ag^+ ions in solution, which gain electrons and are displaced as solid silver atoms. ((c)) Fe(s) + 2Ag^+(aq) → Fe^2+(aq) + 2Ag(s). Part (a): Observations after the reaction - A grey/dark, metallic-looking deposit of silver forms on the surface of the iron wire. - The originally colourless silver nitrate solution gradually turns a very pale green, as iron(II) ions, Fe^…

IGCSE Chemistry 0620: Displacement of Silver by Iron (Ionic Equation)

Part (a): Observations after the reaction

A grey/dark, metallic-looking deposit of silver forms on the surface of the iron wire.
The originally colourless silver nitrate solution gradually turns a very pale green, as iron(II) ions, $\text{Fe}^{2+}(aq)$ , form in its place.

Part (b): Explaining the displacement

Iron is higher in the reactivity series than silver, which means iron atoms have a greater tendency to form positive ions than silver does.

Each iron atom loses two electrons to become an $\text{Fe}^{2+}$ ion. This is oxidation.
These electrons are transferred to $\text{Ag}^+$ ions already dissolved in the solution, which gain electrons to become solid silver atoms. This is reduction.

Because iron’s atoms give up electrons more readily than silver’s ions do, the reaction proceeds with iron going into solution as ions, and silver coming out of solution as solid metal.

Part (c): Ionic equation

One iron atom releases 2 electrons, so 2 silver ions are needed to accept them (1 electron each):

$\text{Fe}(s) + 2\text{Ag}^+(aq) \rightarrow \text{Fe}^{2+}(aq) + 2\text{Ag}(s)$

The nitrate ions, $\text{NO}_3^-(aq)$ , take no part in the reaction (they are spectator ions), so they are correctly left out of the ionic equation.

Final answers

(a) Grey/dark metallic silver deposit on the iron; solution turns pale green.
(b) Iron has a greater tendency to form positive ions than silver (it is more reactive); iron atoms lose electrons, which are transferred to $\text{Ag}^+$ ions.
(c) $\text{Fe}(s) + 2\text{Ag}^+(aq) \rightarrow \text{Fe}^{2+}(aq) + 2\text{Ag}(s)$