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Sunday, February 6, 2022

Handicrafts - III. deciphering secret letters

Handicrafts - III. deciphering secret letters Many chemical reactions are accompanied by color changes. For example, colorless phenolphthalein reagent turns red when encountering alkaline solution, starch solution turns blue when encountering elemental iodine, potassium thiocyanide solution reacts with Fe3 + to produce blood red ferric thiocyanide... While acetic acid solution can react with lignocellulose in paper to produce cellulose acetate, which reduces the ignition point of paper, It is easy to decompose and carbonize when heated. � Tools and materials Brush, beaker, alcohol lamp, scissors. � White paper, colorless phenolphthalein solution, 0.4% sodium hydroxide solution, 2% starch solution, 2% iodine solution, 5% potassium thiocyanide solution, 5% ferric chloride solution and 30% acetic acid solution. � Activity process 1. Divide the students into groups A and B, each with a piece of white paper and a brush. � 2. Please choose one of phenolphthalein solution, starch solution, potassium thiocyanate solution and acetic acid solution and write a secret letter. The content should be healthy and upward. � 3. After drying the secret letter, group A and group B exchanged letters with each other. � 4. Cut some pieces of secret letter paper, and then apply sodium hydroxide solution, iodine solution and ferric chloride solution on the paper in turn to observe whether there is color change. � 5. If there is no color change, bake the paper near the flame of the alcohol lamp and observe whether there are pre carbonized handwriting. � 6. According to the change of the color of the paper, determine which solution is used to write the secret letter, and decipher the content of the secret letter. Description and extension 1. The drugs in this experiment can be selected and used according to specific conditions, or can be replaced by other drugs. � 2. The secret letter can also be written in advance by the teacher, and the students will have a decoding competition in groups. Finally, the students with fast decoding speed are invited to introduce their experience.

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