Chemical changes the color, 5 Experiments
As for the color of the substance, the color that reflects sunlight etc. can be seen. Which color is reflected has a lot to do with the structure of the substance. When the structure of a substance changes due to a chemical change, the color changes. All indicators use this property to change color. This is called the structural color.
Experiment 1: Color change due to reduction ①
you need : 4 g of glucose, 2 g of sodium hydroxide, a little methylene blue, 200 ml of water, PET bottle
Dissolve 2 g of sodium hydroxide in 200 ml of water. Add 4g of glucose and a small amount of methylene blue. Initially, the liquid turns blue, but after a while it returns to transparent. If you shake this, it will turn blue again. Methylene blue is originally blue. However, glucose in an aqueous solution is a reducing sugar that reduces methylene blue. This results in a colorless liquid. When shaken, it is oxidized by oxygen in the air and returns to its original blue color.
Experiment 2: Color change due to reduction ②
you need : glucose 4g, sodium hydroxide 2g, indigo carmine, water 200ml, PET bottle
In the same way, completely dissolve 2 g of sodium hydroxide in 200 ml of water and add 4 g of glucose. Add a small amount of indigo carmine there. It turns green, but eventually it changes from reddish brown to yellow and stabilizes. Shake it lightly to turn it reddish brown, and shake it further to turn it green. It is oxidized by the oxygen in the bottle and changes color. After a while, it is reduced by glucose and returns to its original yellow color. If so, I wonder if other indicators can be used, but if the structure does not change depending on oxygen or glucose, the color will not change.
Experiment 3: Color change of iodine reaction due to temperature change
you need : starch aqueous solution, iodine solution, heating equipment, ice water
The iodine reaction is a familiar reaction. Iodine enters the spiral structure of starch, and the structure changes to develop color. The color disappears when the temperature is raised, and returns when the temperature is lowered. You can do it as many times as you like.
When iodine solution is added to starch aqueous solution, it becomes bluish purple. When this is heated, it becomes transparent as shown in the photo. If you soak it in ice water and lower the temperature, it will turn blue-purple again. You can repeat it as many times as you like.
Experiment 4: Color change of thermo-ink
you need : Thermo-ink, heating equipment, erasable ballpoint pen
Thermo ink familiar in elementary school. This also changes color as the structure changes due to temperature changes. An erasable ballpoint pen that was popular for a while. This also disappears when the temperature rises due to friction. This is designed so that it will not return to its original state even if it gets cold.
Experiment 5: Color change of indicator
al: Purple cabbage (plants containing anthocyanins such as morning glory, standing aoi, eggplant, blueberry, hibiscus)
The structure of a substance called anthocyanin changes depending on the liquid nature such as acidity and alkalinity. And it shows a beautiful color. Please try it by extracting with water, hot water or ethanol.
Well, we have dealt with many color changes, but substances whose structure changes in this way are called chromic substances. There are various types such as those that change with temperature (thermochromic), those that change with ultraviolet rays (photochromic), and those that change with electricity (electrochromic).