Photo decomposition

 Here’s a student-friendly explanation of Activity 1.8 – Photolytic Decomposition of Silver Salts, based on NCERT Class 10 Science, Chapter 1, designed for classroom teaching, note-making, and interactive discussions.

🌞 Activity 1.8 – Photodecomposition of Silver Chloride

(Chapter 1: Chemical Reactions and Equations – CBSE Class 10)

🎯 Objective:

To observe how sunlight causes the decomposition of silver chloride into silver metal and chlorine gas.

🧰 Materials Required:

  • 2 g of silver chloride (AgCl)

  • China dish

  • Access to sunlight

🔍 Procedure:

  1. Take about 2 g of silver chloride in a china dish.

  2. Observe its initial colour — it is white.

  3. Place the dish under sunlight for some time.

  4. Observe the colour change of the substance.

👁️ Observation:

  • Silver chloride (AgCl) changes from white to grey.

  • This indicates the formation of silver metal.

  • The change is due to the action of sunlight breaking down AgCl.

🧪 Chemical Reaction:

2AgCl(s)→Sunlight2Ag(s)+Cl2(g)2\text{AgCl} (s) \xrightarrow{\text{Sunlight}} 2\text{Ag} (s) + \text{Cl}_2 (g)

  • AgCl → Silver chloride (white)

  • Ag → Silver metal (grey)

  • Cl₂ → Chlorine gas (not visible)

⚡ Photolytic Decomposition:

A photolytic (or photochemical) decomposition is a reaction where a compound breaks down due to the action of light.

✅ Type of Reaction: Decomposition
✅ Energy Source: Sunlight (light energy)
✅ Also called: Photodecomposition Reaction

🧪 Another Example – Silver Bromide:

2AgBr(s)→Sunlight2Ag(s)+Br2(g)2\text{AgBr} (s) \xrightarrow{\text{Sunlight}} 2\text{Ag} (s) + \text{Br}_2 (g)

  • AgBr is also light-sensitive, turning grey in sunlight.

📸 Real-Life Application – Photography:

  • These reactions are used in black and white photography.

  • Silver halides (AgCl, AgBr) are used in photo films.

  • Light exposure causes decomposition → creates image on film.

📘 Classroom Recap Table:

Substance Before Sunlight After Sunlight Gas Released Type of Reaction
AgCl White Grey (Ag metal) Chlorine (Cl₂) Photolytic decomposition
AgBr Pale yellow Grey (Ag metal) Bromine (Br₂) Photolytic decomposition

🎤 Teacher's Wrap-up Line:

“A photograph may be worth a thousand words, but it starts with just a bit of chemistry — silver salts turning into silver under the sun!”

Would you like a photography-in-chemistry fact sheet, lab demonstration plan, or a student quiz based on photodecomposition?

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