How do indicators tell that something is a acid or a base? My teacher also said they can only tell once the acid or base is in water? Is this true and if yes. Then would these not be able to tell wheatgerm something is acadic or basic if we put it in complete form of it like not in water? Like its raw form.
In: Chemistry
Indicators are chemicals that change color in response to pH of the solution. The solution is going to be both the chemical that is an acid or base, and something for that chemical to dissolve in, which is almost always going to be water. There are a lot of different chemicals that can be used as indicators and which will change colors at different pHs.
Pure water has a pH of about 7, so if you add something to water and the pH changes, you can tell if that chemical is an acid or a base. If you take something like wheatgerm and grind it into a fine powder and mix it with water, then if the pH of the water drops, you know that the reason for the drop is the added chemicals, and from this conclude that wheatgerm is an acid, even when not mixed with water. Remember that an acid is generally a hydrogen ion donor, while a base is a hydrogen ion acceptor. Just because the wheatgerm sitting dry on the shelf isn’t melting the container doesn’t mean it isn’t an acid (or a base, as the case might be). It is an acid because of how it reacts with other materials, like water.
Indicators work because they have multiple atoms that can lose or gain a proton, which changes the way light is absorbed by the molecule. In acids, there are more protons in solution and in bases, there are more proton accepting ions, so fewer free protons. If there are a bunch of protons in solution, they’ll want to naturally bond with something, and indicators have places for them to do that. When there are a lot of proton acceptors on solution, they want to bond with protons, so the indicator will donate their proton. These changes then lead the molecule to exhibit a different color.
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