If you have ever looked through a chemistry textbook, chances are you are familiar with a certain image: that of a nerdy kid wearing nerdy goggles who is examining beakers full of colorful liquid. As if glassware filled with water and food coloring is supposed to inspire you in your battle with stoichiometry. While the scene may be cliche, it illustrates something significant. It may surprise you to know that colors represent a big part of chemistry. If you remember, colors are just different wavelengths of light. You might also recall that different substances reflect some wavelengths but not others. For example, a red apple reflects red light while absorbing most other colors. This is because the molecular structure of the apple's skin allows the non-red wavelengths to pass into it. Essentially, a chemical's color is a literal reflection of its molecular construction. This makes color a useful tool when you consider that chemistry is the study of matter.
As usual, I performed an experiment that related to this concept. To start, I added some water to the bottom of a large flask. I then stirred in a small amount of potassium permanganate crystals (KMnO4). When the crystals dissolved, I had a dark purple solution. Next, I prepared a second solution of hydrogen peroxide (H2O2) and sulfuric acid (H2SO4). With my camera ready, I began pouring the mixture into the large flask. As the two liquids met, something astonishing happened. Within seconds, the purple color of the first solution had disappeared. The contents of the flask had gone from dark purple to crystal clear in an instant.
The speed at which the reaction took place gave me an idea. I wanted to see what would happen if I reversed the positions of two liquids. So after adding the hydrogen peroxide and sulfuric acid to the big flask, I made another solution of potassium permanganate in a separate beaker. Now came the test. I held the beaker above the flask and slowly poured out its colorful contents. As I did, something magical happened. Upon landing in the flask, the purple solution became invisible. Even after emptying the entire beaker, the liquid in the flask remained as clear as water. The effect was simple yet quite satisfying.
As usual, I performed an experiment that related to this concept. To start, I added some water to the bottom of a large flask. I then stirred in a small amount of potassium permanganate crystals (KMnO4). When the crystals dissolved, I had a dark purple solution. Next, I prepared a second solution of hydrogen peroxide (H2O2) and sulfuric acid (H2SO4). With my camera ready, I began pouring the mixture into the large flask. As the two liquids met, something astonishing happened. Within seconds, the purple color of the first solution had disappeared. The contents of the flask had gone from dark purple to crystal clear in an instant.
The speed at which the reaction took place gave me an idea. I wanted to see what would happen if I reversed the positions of two liquids. So after adding the hydrogen peroxide and sulfuric acid to the big flask, I made another solution of potassium permanganate in a separate beaker. Now came the test. I held the beaker above the flask and slowly poured out its colorful contents. As I did, something magical happened. Upon landing in the flask, the purple solution became invisible. Even after emptying the entire beaker, the liquid in the flask remained as clear as water. The effect was simple yet quite satisfying.
Surprisingly, both of these demonstrations have a simple explanation. When the two liquids met, a chemical reaction occurred. While I won't go into detail, the hydrogen peroxide and sulfuric acid caused the potassium permanganate to break apart and form smaller pieces. But how does this explain the color change? Well, as a mentioned before, different substances reflect different colors. In the case of the potassium permanganate, it was reflecting purple light. However, thanks to the chemical reaction, it was transformed into different substances. And unlike the potassium permanganate, these substances did not reflect purple light. In fact, they barely reflected any light, which is why they appeared colorless.
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| The demonstration's simple yet satisfying nature makes it one of my favorites. |
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