What is the color of water?

Thanks to Alan Babu for the request.

This is not so easy to answer.First, we need to clarify what color is.

What is color?

Color is ultimately light, or more precisely, the targeted absence of light.

Light is known to be both waves and particles at the same time.But for this discussion, we are sticking to the waves.

Pure, complete light is white by definition.This “white” consists of the entire color spectrum or the colour gamut. On this scale there is a kind of “temperature”, i.e. how much energy or energy. which wavelength the light has. In a certain range of wavelengths, this form of radiation is visible to the human eye. That’s why we call it “visible light.” This “temperature” is measured in Hertz (Hz) and refers to the wavelength of radiation — i.e. how far apart the highs and lows of the waves are.

However, there are also invisible Light.Infrared, UV, radio waves, X-rays: these are all forms of light that we cannot perceive without devices.Infrared is so to speak “reder than red” and UV (ultraviolet) is so to speak “violet than violet” because they are just outside our perception.

It’s a bit like an old analog radio.A FM radio can only use radio waves or “see” light between 87.5 and 108.0 MHz. Our eyes only see light between 430 and 770 THz. But in both cases, there are huge areas in the spectrum outside of perception.

This means that all wavelengths are equally represented in pure white light.


At the top all radiation, at the bottom only the visible area magnifies. Source: Surfertoday.com

How does color come about?

Color is created in two ways: reflective (i.e. mirrored) or active (from a light source).

The moon reflects light and is reflective; the sun generates light and is active.

Each element absorbs light. Thus, even if the light source “sends” purely white, the light is filtered by what is between the eye and the light source.Some substances absorb a lot, others little — but there is always something left behind and/or mirrored.

With reflection, the surface absorbs wavelengths of light, depending on the composition.”Red” color thus reflects all colors except red. Our perception of mirrored light can be repeated through air, windows, water, etc. to change the color again. Thus, the painted red can appear in a different light, if the light source is not pure white, or if the air has any unusual gas mixtures, or if you look at the red through a window pane. This all has an impact on the perception of color.

So even air has a “color”.However, the air takes away as little light as a weak filter that we cannot perceive it at normal distances. Unless we look up — we see that the air is blue.

But here comes the counterintuitive part.The light is blue.But because the many oxygen in the atmosphere only absorbs or scatters blue wavelengths, we don’t actually see blue, but anything but blue together. But we just perceive it as “blue”.

With a spectrometer you can see it wonderfully.The whole spectrum is represented, but only blue is not. This allows us to determine which elements are in the air.

(Before the physicists jump into my neck, yes, that’s very simplified.)

Now off into the water

The same principle applies to water.Again, the oxygen in the water (chemical composition two atoms hydrogen H and one atom oxygen O) absorbs or scatters targeted blue light, but now significantly more than air, for the most part because the molecules of the water much are closer together than those in the air.(If you boil the water into steam, the molecules spread drastically and the steam is no longer a liquid, but a gas like the air.)

This means that small amounts of water — even distilled pure [mathH_2O[/math — appear clear and colourless, because our eyes cannot perceive the minimal dispersion of the blue light in a differentiated way.But the more water, the more scattering — and the clearer the blue color.

This also applies to other “clear” substances such as glass.The thicker the glass, the more you see the color (mostly greenish).

But why does hydrogen H not play a major role, even though there are two atoms for each oxygen atom?Quite simply: hydrogen atoms are much smaller, ultimately just a proton, (usually) a neutron and an electron. Oxygen has 8, eight times as much mass as hydrogen. (That’s why it’s a bit ironic that it’s called “hydrogen.” Oxygen would be more important from the mass.)

But even if the atoms have significantly different mass, they are similar in size — hydrogen 120 pm, oxygen 152 pm. So the oxygen atom is much more densely packed and heavier.


Pure water is blue.

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