Flame test colours Flashcards
How do you perform a flame test?
-Safety glasses fume cupboard lab coat
-dip the nichrome wire into the conc HCL then into the
metal compound (powdered)
-hold the end of the wire in the flame and observe the colour of the flame
Flame test colour: Lithium (1)
Red (Li+)
Flame test colour: Sodium (1)
(Na+) yellow/orange
Flame test colour: Potassium (1)
(K+) lilac
Flame test colour: Rubidium (1)
(Rb+) red/purple
Flame test colour: Caesium (1)
(Cs+) blue/violet
Flame test colour: Magnesium (2) & Beryllium (2)
(Be2+&Mg2+) no colour (yellow)
Flame test colour: Calcium (2)
(Ca2+) (brick) red
Flame test colour: Strontium (2)
(Sr2+) (crimson) red
Flame test colour: Barium (2)
(Ba2+) (apple) green
What causes the colours in flame tests?
- electrons absorb energy and move to a higher energy level
- this electron is now in an excited state
- the electron immediately drops back to its “ground state”
- this movement releases energy as light
- if the light released is in the visible spectrum we can then perceive it as colour
What are the 2 main problems with a flame test?
- Many compounds contain small amounts of sodium so the intense colour of Na can mask other colours
- Qualitative test
Give two reasons why the wire is made of nichrome and not iron
- The iron can react with the oxygen in the air forming iron oxide
- Nichrome wire is unreactive compared to iron
- Iron can produce sparks / colours
Give a reason why the wire is dipped into acid and then heated in the first stage.
-Heated to remove any residual metal from previous tests
State why fresh concentrated hydrochloric acid is used in the second stage of
the flame test
-To prevent contamination of the acids with metals from the previous test
