Thursday 7 August 2014

Flame test

Flame test

Description:  Small amounts of different salts are burned in the flame of a Bunsen burner.  Sodium burns orange, potassium - purple/blue, barium - green, and lithium – red

Concept:   When an element is burned, the electrons will be excited.  Then as these electrons fall back from one energy level to another, they will emit photons of light.  These photons will have different colors depending on the element and its discrete energy levels.  That is, different wavelengths of light (colors) will be emitted when the electrons of  different elements go down the step(s) between their energy level(s).  Each element will have its own set of steps, therefore each will have its own color.
 
Procedure: 
            Dip the wire loop of a glass rod into the water/con.HCI
            Use this wet loop to pick up some salt.
            Hold the salt in the flame and burn to show color.
            Do the same for all salts, being sure to use a different glass rod-with-wire loop
for each salt.  Also be careful not to drop any salt onto the Bunsen burner.

Clean-up:  Be sure to turn the gas off if you use a Bunsen burner.  In rm. 122 you will need to have Alice open the cupboard to get to the gas valve.  Wash wire loops well to
ensure all salt is removed.  Clean off any salt that might have dropped onto the Bunsen burner or propane torch.


Flame Test Colors
Li+                                        Deep red (crimson)
Na+                                       Yellow
K+                                         Violet
Ca2+                                      Orange-red
Sr2+                                      Red
Ba2+                                      Green
Cu2+                                     Blue-green

Cu1+                                     Green
Cu2+                                     Blue
Fe                                         Yellow to red-orange (depending on anion and charge of Fe); in
                                               rare cases, can form complex ion with a deep blue color
Fe2+                                      yellow-green (depending on the anion)
Fe3+                                      orange-red (depending on the anion)
Co2+                                     Pink      
Cr3+                                      Violet  to Green
Ni2+                                      Green
Mn2+                                    Pink
Pb3+                                      blue-green (Pb2+ and Pb4+ are colorless)
V2+                                       violet
V3+                                       blue-green
MnO4-                                  Purple (Mn w/ +7 oxidation state is purple)
CrO42-                                  Yellow
Cr2O72-                                Orange
Cu(NH3)42+                         Dark Blue; produced when ammonia is added to Cu2+ solutions
FeSCN2+                              Red-brown, Wine-red to dark orange
CoCl42-                                Blue (Co2+ with HCl will form a CoCl42- complex that is blue)
Ti(H2O)63+                           Purple

 






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much love
nayu

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Mudassar Husain

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