[Ice-cream]

Can any1 tell me if CrO4 (2-) is the formula for a chromate ion? Also, does any1 know the wavelength of it or the colour of light it absorbs? (I've looked on the web and there are diff. answers...) Can some1 plz help me?

[charco]

yes it is...

eg potassium chromate K2CrO4

It shows yellow and so I would imagine that it absorbs in the red end of the visible spectrum

green + blue = yellow

this suggests that it abosrbs in the red end of the spectrum 650 - 700 nm

[Ice-cream]

but if it shows as yellow, then doesn't it absorb purple light (because of complementary colours)?

[Garneck]

540 nm (or at least that's the wavelength at which you determine chromates)

If you want to read something in polish, you will find it under "chromiany"
http://www.aqualab.com.pl/kat_2002/62_69.pdf

[charco]

540nm is green light

[Ice-cream]

im getting confused...ok, from what i've read from websites is that chromate will show as yellow. Since it's complementary colour is purple, that's the colour that it absorbs...but that makes it's wavelength fall in the range of 400nm to 430nm...(but i don't think its wavelength falls in that range; according to u guys its wavelength is about 540nm. i saw on a website that the wavelength is 530nm, and then i saw on another website that its 3 hundred and something nm...)

so can any1 help me sort out this problem?

[Ice-cream]

So no one knows about the colour of the light absorbed by chromate ion? Or its wavelength?

[kevins]

As I know, 540nm is used for the reaction of Diphenylcarbohydrazide to Cr(6).
As the chromate is yellow, so the wavelength should be around 450nm. You can try to scan the max absorbance against the wavelength by the spectrophotometer.