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We usually explain flame test as when valence e- are excited and come back, it produces colour ,2 ques: 1- in lab, we use a salt, say CaCl2, in this, Ca is +2 i.e. no valence e-, so how does it shw flame test? 2- as we go down group flame turns from red to blue, why?

We usually explain flame test as when valence e- are excited and come back, it produces colour ,2 ques:


1- in lab, we use a salt, say CaCl2, in this, Ca is +2 i.e. no valence e-, so how does it shw flame test?


2- as we go down group flame turns from red to blue, why?

Grade:12

1 Answers

SAGAR SINGH - IIT DELHI
878 Points
13 years ago

Dear saransh,

Flame test, test used in the identification of certain metals. It is based on the observation that light emitted by any element gives a unique spectrum when passed through a spectroscope. When a salt of the metal is introduced into a Bunsen burner flame, the metallic ion produces characteristic color in the flame. Some metals and the colors they produce are: barium, yellow-green; calcium, red-orange; copper salts (except halides), emerald green; copper halides or other copper salts moistened with hydrochloric acid, blue-green; lithium, crimson; potassium, violet; sodium, yellow; and strontium, scarlet. The value of this simple flame test is limited by interferences (e.g., the barium flame masks calcium, lithium, or strontium) and by ambiguities (e.g., rubidium and cesium produce the same color as potassium). A colored glass is sometimes used to filter out light from one metal; for instance, blue cobalt glass filters out the yellow of sodium.

 

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Sagar Singh

B.Tech, IIT Delhi

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