Unveiling the Colour Secrets of Chemicals: Understanding CuSO4 and PbI Hue

[phy1210]

I know that CuSO4 is blue or PbI is yellow.

Is there any way to remember the colour of all chemicals?

 

[member 392791]

As far as remembering I don't think (unless you attempt to brute force memorize). Alternatively, you can find the crystal field split energy and equate it to hc/λ, solving for λ will give you the wavelength, which you can then determine the color.

http://en.wikipedia.org/wiki/Crystal_field_theory

 

[phy1210]

That would be difficult to use. I only have a periodic table for exams!

 

[Borek]

There is no simple and reliable method other then memorization. But then you don't have to remember everything, just about a dozen most common compounds. You can safely assume all inorganic compounds not containing transition metals are white.

 

[Jimmy Snyder]

What color is blue vitriol?

 

[epenguin]

Do you get much lab work or demonstrations? I think a point of lab work is those things become hard to forget! Equally if you are never in a lab I wonder if there is all that much point in knowing the colours.

One help for memorising would be to know - find out - their uses, and particularly coloured ones tend to be used, naturally, in paints and pigments.

So for instance "Lead iodide is toxic due to its lead content. In the nineteenth century it was used as an artists' pigment under the name Iodine Yellow, but it was too unstable to be useful" from Wiki.

 

[AGNuke]

Some colours you may know:

Cu²⁺ salts like CuSO₄ or CuCO₃ are blue.

Fe²⁺ are light green.

Fe³⁺ are yellow (light I think).

I^- are dark yellow.

Br^- is pale yellow.

And some transition element-containing anions may exhibit colours, like permanganate are magenta, manganate are dark green, dichromate are orange, etc.

As far you are concerned, these trends are more than enough to run your life for quite a while. I too rode on these trends.

 

[phy1210]

@Borek - I was hoping for some mnemonic to memorize these colours

@epenguin - I have an Alternative to Practical Examination which encourages the chem teachers not to do practical. That's the problem!

@AGNuke - I was told that we would be asked colours of basic elements. So, Thanks!

 

[epenguin]

The names of at least 11 elements refer to a colour.

http://en.wikipedia.org/wiki/List_of_chemical_element_name_etymologies

 

[chemisttree]

Some colours you may know:

Cu²⁺ salts like CuSO₄ or CuCO₃ are blue.

Fe²⁺ are light green.

Iron(II) oxide is black.

Fe³⁺ are yellow (light I think).

Iron(III) nitrate is colorless. Iron(III) chloride is yellow.

I^- are dark yellow.

Potassium iodide is colorless.

Br^- is pale yellow.

Sodium bromide is colorless.

@Phy1210... you spelled 'color' wrong.

 

[member 392791]

Maybe he is British?

 

[JohnRC]

The colours of "main group" element compounds are about 90% white or colourless. Main group meaning periodic groups 1,2, and 13-18. Group 12 compounds are also usually colourless (zinc cadmium and mercury). Salts of the heaviest elements in the main groups -- thallium, lead, and bismuth, tend to be straw coloured ranging to yellow. Materials that are electrical conductors are opaque and greyish; semiconductors are opaque and usually quite black.

The other transition metals (Groups 3-11) each have a characteristic colour for compounds of each of their several oxidation states, but there is little system to the colours, and nearly as many exceptions as rule-following examples. Lanthanides have characteristically very pale pastel colours for their typical (oxidation state III) compounds, but cerium(IV) compounds are typically bright yellow.

 

[chemisttree]

Maybe he is British?

 

[AGNuke]

Iron(II) oxide is black.


Iron(III) nitrate is colorless. Iron(III) chloride is yellow.


Potassium iodide is colorless.


Sodium bromide is colorless.

I know some compounds do not exhibit colours/different colours from what I have given. Since he asked that question, I had an instinct that in early school, some fixed compounds are asked only, like Lead Iodide or Silver Iodide, Copper/Ferrous/Ferric Sulphate, as they can easily be found in school lab.

I am also undergoing the same phase, being doing some Salt Analysis practicals. I rote these colours down as confirmatory tests because I seldom go to school and secondly, schools do not have much to teach really so I just learned that the test of salt containing Iodides (KI commonly given) is to precipitate it with Silver Nitrate to get a yellow ppt.