Magic Writing

Secret messages become visible.

Scientific name: Colored products are obtained in 5 different reactions.

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Safety

Wear eye protection goggles and gloves.Perform this experiment in a well ventilated room.

Always follow general safety recommendations. Please note that conducting chemistry experiments you must comply with the relevant legal procedures in your country.

Reaction formula

2KNO3 → 2KNO2 + O2

Pb2+(aq) + 2I-(aq) → PbI2(s) (yellow)

(Fe(H2O)6)3+(aq) + CNS-(aq) → (Fe(CNS)(H2O)5)2+ (aq) (red-brown)

phenolphthalein (colorless) -(NH3(aq), pH change)→ phenolphthalein (pink)

(Cu(H2O)6)2+(aq) + 4NH3(aq) → (Cu(NH3)4(H2O)2)2+(aq) + 4H2O(l) (blue)

Step-by-step instruction

  1. Prepare a small paint brush and a piece of filter paper. Write a secret message with saturated potassium nitrate solution. Use cursive writing.
  2. Put a small pencil mark at the beginning of the message.
  3. Dry the paper.
  4. Light up the splint.
  5. Put the glowing splint next to the pencil spot on the filter paper.
  6. It will ignite the paper where potassium nitrate was placed.
  7. Prepare solutions of iron (III) nitrate, lead(II) nitrate, aqueous ammonia, potassium iodide, potassium hexacyanoferrate(II), ammonium thiocyanate, phenolphthalein and copper sulphate.
  8. Pour solutions of iron (III) nitrate, lead(II) nitrate and aqueous ammonia into spray bottles.
  9. Write or paint something on filter paper with a paint brush soaked in solutions of potassium iodide, potassium hexacyanoferrate(II), ammonium thiocyanate, phenolphthalein and copper sulphate.
  10. Let the papers with the messages dry.
  11. To revel the message written with potassium iodide, spray the filter paper with the solution of lead nitrate. The text turns yellow.
  12. To revel the message written with potassium hexacyanoferrate(II), spray the filter paper with solution of iron (III) nitrate. The text turns dark blue.
  13. To revel the message written with ammonium thiocyanate , spray the filter paper with solution of iron (III) nitrate. The text turns red-brown.
  14. To revel the message written with phenolphthalein , spray the filter paper with aqueous ammonia. The text turns pink.
  15. To revel the message written with copper sulphate, spray the filter paper with aqueous ammonia. The text turns blue.
  16. To make red-brown text of iron thiocyanate (the message initially written with ammonium thiocyanate) disappear again spray it with aqueous ammonia.

Scientific background

This experiment demonstrates different ways to write secret messages. The first one is writing with fire. The text written with saturated solution of potassium nitrate glows and burns leaving the rest of paper untouched. The reason of this process – thermal decomposition of potassium nitrate:

2KNO3 → 2KNO2 + O2

Released oxygen promotes the combustion process.

In the second part of the experiment a number of colorless solutions are used to write messages. The text becomes visible when the paper with the message is treated with another solution. Chemical reactions between components give colored products:

Pb2+(aq) + 2I-(aq) → PbI2(s) (yellow)

Reaction between iron(III) nitrate and hexacyanoferrate(II) ions gives intense blue colour because of formation of compound known as Prussian blue. It is a complex formula with general formula Fex(CN)y.zH2O.

(Fe(H2O)6)3+(aq) + CNS-(aq) → (Fe(CNS)(H2O)5)2+ (aq) (red-brown)

phenolphthalein (colorless) -(NH3(aq), pH change)→ phenolphthalein (pink)

(Cu(H2O)6)2+(aq) + 4NH3(aq) → (Cu(NH3)4(H2O)2)2+(aq) + 4H2O(l) (blue)

Danger:
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Published on 30 March 2015

  • Fire
  • Heating with fire
  • Explosion
  • Poisoned gas
  • Organic
  • Electricity
  • Solution
  • Oxidation reduction
  • Color change
  • Precipitate
  • Gassing
  • Catalyst