Silver (Ag): Chemical Reactions & Properties Study Guide

Chemical Properties Overview

Silver (Ag), a noble metal, is located in Group 11, Period 5 of the periodic table. Its chemical inertness is attributed to its high ionization enthalpy and standard electrode potential.

• Reactivity Series Position: Silver is positioned below hydrogen and copper in the electrochemical series. This indicates its low reactivity with non-oxidizing acids and its resistance to easy oxidation.
• Electronegativity: Approximately 1.93 on the Pauling scale.
• General Reactivity: Silver is known for its relatively low chemical reactivity. It resists attack by oxygen and water under normal conditions but readily tarnishes in the presence of sulfur compounds. It reacts with strong oxidizing acids.

Action of Air and Oxygen

Silver does not react with dry air or oxygen at ordinary temperatures, maintaining its lustrous appearance. However, it tarnishes slowly in the presence of hydrogen sulfide (H₂S) gas in the air, forming a black layer of silver sulfide (Ag₂S). This process is known as tarnishing.

• Tarnishing in Moist Air containing H₂S: $$4\text{Ag(s)} + 2\text{H}_2\text{S(g)} + \text{O}_2\text{(g)} \longrightarrow 2\text{Ag}_2\text{S(s)} + 2\text{H}_2\text{O(l)}$$

Action of Water and Steam

Silver is highly resistant to reaction with water or steam. It does not react with water even at elevated temperatures.

• With Water/Steam: $$\text{Ag(s)} + \text{H}_2\text{O(l/g)} \longrightarrow \text{No Reaction}$$

Action of Acids and Bases

Action of Acids

Due to its position below hydrogen in the reactivity series, silver does not react with non-oxidizing acids like dilute hydrochloric acid (HCl) or dilute sulfuric acid (H₂SO₄). However, it reacts with oxidizing acids.

1. With Non-Oxidizing Acids (e.g., Dilute HCl, Dilute H₂SO₄): $$\text{Ag(s)} + \text{HCl(dilute)} \longrightarrow \text{No Reaction}$$ $$\text{Ag(s)} + \text{H}_2\text{SO}_4\text{(dilute)} \longrightarrow \text{No Reaction}$$

2. With Dilute Nitric Acid (HNO₃): Silver reacts with dilute nitric acid to produce silver nitrate, nitric oxide, and water. $$3\text{Ag(s)} + 4\text{HNO}_3\text{(dilute)} \longrightarrow 3\text{AgNO}_3\text{(aq)} + \text{NO(g)} + 2\text{H}_2\text{O(l)}$$

3. With Concentrated Nitric Acid (HNO₃): Silver reacts with concentrated nitric acid to form silver nitrate, nitrogen dioxide, and water. $$\text{Ag(s)} + 2\text{HNO}_3\text{(conc)} \longrightarrow \text{AgNO}_3\text{(aq)} + \text{NO}_2\text{(g)} + \text{H}_2\text{O(l)}$$

4. With Hot Concentrated Sulfuric Acid (H₂SO₄): Hot concentrated sulfuric acid oxidizes silver to silver sulfate, evolving sulfur dioxide gas and water. $$2\text{Ag(s)} + 2\text{H}_2\text{SO}_4\text{(conc, hot)} \longrightarrow \text{Ag}_2\text{SO}_4\text{(aq)} + \text{SO}_2\text{(g)} + 2\text{H}_2\text{O(l)}$$

Action of Bases

Silver does not react with aqueous solutions of common strong bases (alkalis) like sodium hydroxide (NaOH) or potassium hydroxide (KOH).

• With Alkalis: $$\text{Ag(s)} + \text{NaOH(aq)} \longrightarrow \text{No Reaction}$$

Key Laboratory Test/Identification Reactions for Silver Ion (Ag⁺)

Silver ions (Ag⁺) are commonly identified in qualitative inorganic analysis through their characteristic reactions.

1. Chloride Test (Reaction with Hydrochloric Acid or Soluble Chlorides): Adding dilute hydrochloric acid or a solution of a soluble chloride (e.g., NaCl) to a solution containing Ag⁺ ions produces a white curdy precipitate of silver chloride (AgCl). $$\text{Ag⁺(aq)} + \text{Cl⁻(aq)} \longrightarrow \text{AgCl(s)}$$

   • Confirmatory Test 1: Solubility in Ammonium Hydroxide: The white precipitate of AgCl is soluble in aqueous ammonia (ammonium hydroxide), forming a colorless soluble complex, diamminesilver(I) chloride. $$\text{AgCl(s)} + 2\text{NH}_3\text{(aq)} \longrightarrow [\text{Ag(NH}_3\text{)}_2]\text{Cl(aq)}$$
   • Confirmatory Test 2: Reprecipitation with Acidification: Upon adding dilute nitric acid (HNO₃) to the diamminesilver(I) complex solution, the AgCl precipitate reappears. $$[\text{Ag(NH}_3\text{)}_2]\text{Cl(aq)} + 2\text{H⁺(aq)} \longrightarrow \text{AgCl(s)} + 2\text{NH}_4\text{⁺(aq)}$$

2. Chromate Test (Reaction with Potassium Chromate): Adding potassium chromate (K₂CrO₄) solution to a solution containing Ag⁺ ions produces a reddish-brown precipitate of silver chromate (Ag₂CrO₄). This test is also used in Mohr’s method for chloride estimation. $$2\text{Ag⁺(aq)} + \text{CrO}_4\text{²⁻(aq)} \longrightarrow \text{Ag}_2\text{CrO}_4\text{(s)}$$