18.8 What salts change the colour of flames?
Description
This article is from the Chemistry FAQ, by Bruce Hamilton B.Hamilton@irl.cri.nz with numerous contributions by others.
18.8 What salts change the colour of flames?
Both Vogel ( qualitative inorganic ) and the Rubber Handbook list details of
flame tests for elements. The spectra of the alkaline earth compounds are
relatively complex, so using filters to view the flame can change the colour
observed as dominant lines are filtered out. In general, except for copper,
any compound of an element can be used, however toxic salts ( such as
cyanides ) should not be used. Halogen salts are usually readily available,
and are reasonably volatile. In all cases, perform experiments in a
well-ventilated area - preferably a fume hood. The emission spectra in the
visible region is the sum of several emission lines, with dominant lines
masking others. The visible spectrum is approximately :-
Red 800 - 620 nm Orange 620 - 600 nm Yellow 600 - 585 nm Green 585 - 505 nm Blue 505 - 445 nm Violet 445 - 400 nm
There are also the various bead tests employing borax ( sodium tetraborate
Na2B4O7.10H2O ), Microcosmic salt ( NaNH4HPO4 ), or sodium carbonate
(Na2CO3), using both oxidising and reducing flames. The bead test procedures
are detailed in Vogel ( qualitative inorganic ), and similar texts.
Element Colour Some of the contributing lines, and comments.
Arsenic Light Blue 449.4 nm, 450.7 nm.
( Arsenic is highly toxic - only perform in fume hood under supervision )
Barium Green-Yellow 553.6 nm, 539.1 nm, 536.1nm, 614.2 nm.
Blue (faint) 455.4 nm, 493.4 nm.
Cesium Red-Violet 852.1 nm.
Calcium Orange 618.2 nm, 620.3 nm.
Yellow-Green 530.7 nm, 559.5 nm.
Violet (faint) 422.7 nm.
Greenish with blue glass.
Copper Emerald Green 521.8 nm, 529.2 nm, 515.3 nm.
Not chloride, or in presence of HCl
Azure Blue 465.1 nm.
Copper chloride, or HCl present
Lead Light Blue 500.5 nm.
( Lead is highly toxic - only perform in fume hood under supervision )
Lithium Carmine Red 670.78 nm, 670.79 nm.
Orange (faint) 610.1 nm.
Violet with blue glass
Potassium Red 766.5 nm, 769.9 nm.
Violet 404.4 nm, 404.7 nm.
Purple-red with blue glass
Rubidium Violet 780.0 nm, 794.8 nm.
Sodium Yellow 589.0 nm, 589.6 nm.
Invisible when viewed with blue glass
Strontium Scarlet Red 640.8 nm, 650.4 nm, 687.8 nm, 707.0 nm.
Violet 460.7 nm, 421.5 nm, 407.8 nm.
Violet with blue glass
Tellurium Green 557.6 nm, 564.9 nm, 566.6 nm, 570.8 nm.
( Tellurium is highly toxic - only perform in fume hood under supervision )
Thallium Green 535.0 nm.
( Thallium is highly toxic - only perform in fume hood under supervision )
Zinc Whitish Green Large number of peaks between 468.0-775.8 nm.
( Zinc fumes are toxic - only perform in a fume hood under supervision )
Impressive coloured flames have been obtained using chlorides and a methanol
flame in a petri dish [6]. Even more spectacular results have been obtained
by nitrating cellulose filter paper, and impregnating it with salts prior
to ignition [7].
Continue to:
My Books
