Two drops of phenol red are added to a solution with a pH of 5.6, what colour will be observed?
I know the colour is yellow, but WHY??
Thanks :)
I know the colour is yellow, but WHY??
Thanks :)
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The indicator molecule has a yellow form which has a H+ ion attached.
When that H+ comes off, the molecule switches to its pink form.
In an acid solution, there are a lot of H+ ions floating around, so there are plenty that could attach to form the yellow molecule.
In a basic solution, there are a lot of OH- ions floating around. They attract the H+ from the yellow molecule to form water, and change the indicator molecule to its pink form.
If that answers you question, you can stop reading now.
A clear liquid allows all the light (red, green, and blue) to pass through.
A colored solution absorbs some colors and lets others through.
So the pink molecule absorbs green light and allows red and blue light to pass through creating the magenta color of the indicator.
And the yellow molecule absorbs blue light and allows red and green light to pass through creating the yellow color. (In additive color mixtures, red + green = yellow.)
Whether a molecule absorbs a color depends how light intereacts with its electrons. If a frequency of light matches the energy difference between energy levels in the molecule, the electron absorbs the energy and moves to a higher energy level. (Imagine two party situations. In the first, you see a number of your friends. It would take a long time to get from one side of the room to the other because you talk with each person you know. In the second, you don't know a soul, and even worse they're your parents' work associates. You've got nothing to say to any of them, so you can walk across the room in no time.)
The characteristic of phenol red that makes it colorful is the alternating double and single bonds in its 3 hexagonal rings. It just so happens that that electron energy arrangement matches the energies of visible light. And gaining or losing the H+ ion changes the energies just enough to give two different colors.
When that H+ comes off, the molecule switches to its pink form.
In an acid solution, there are a lot of H+ ions floating around, so there are plenty that could attach to form the yellow molecule.
In a basic solution, there are a lot of OH- ions floating around. They attract the H+ from the yellow molecule to form water, and change the indicator molecule to its pink form.
If that answers you question, you can stop reading now.
A clear liquid allows all the light (red, green, and blue) to pass through.
A colored solution absorbs some colors and lets others through.
So the pink molecule absorbs green light and allows red and blue light to pass through creating the magenta color of the indicator.
And the yellow molecule absorbs blue light and allows red and green light to pass through creating the yellow color. (In additive color mixtures, red + green = yellow.)
Whether a molecule absorbs a color depends how light intereacts with its electrons. If a frequency of light matches the energy difference between energy levels in the molecule, the electron absorbs the energy and moves to a higher energy level. (Imagine two party situations. In the first, you see a number of your friends. It would take a long time to get from one side of the room to the other because you talk with each person you know. In the second, you don't know a soul, and even worse they're your parents' work associates. You've got nothing to say to any of them, so you can walk across the room in no time.)
The characteristic of phenol red that makes it colorful is the alternating double and single bonds in its 3 hexagonal rings. It just so happens that that electron energy arrangement matches the energies of visible light. And gaining or losing the H+ ion changes the energies just enough to give two different colors.
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Arf