4.15 - Flame Tests and the Test for Ammonium Ions Flashcards
What safety precautions should be considered when doing a flame test?
Wearing safety glasses, a lab coat, and doing the experiment in a fume cupboard
What is used to do the flame test?
A nichrome wire
What must be done to the wire before used for the flame test?
It must be sterilised with nitric acid
Why?
Because it may have other metal compounds on it which would change the colour of the flame
What is added to the metal before putting into the flame?
Hydrochloric acid
Why?
Because it forms a metal chloride, which is more volatile and so will give better results
What is the main impurity in every flame test?
Sodium
What is another problem with flame tests?
Human perception of colour
What colour do lithium ions produce?
Red
What colour do sodium ions produce?
Orange-yellow
What colour do potassium ions produce?
Lilac
What colour do rubidium ions produce?
Red/Purple
What colour do caesium ions produce?
Blue/Violet
What ions produce no colour?
Beryllium and magnesium
What colour do calcium ions produce?
Brick red
What colour do strontium ions produce?
Crimson red
What colour do barium ions produce?
Apple green
What causes these colours to be emitted?
Electron transitions
What happens when electrons absorb energy?
They move to a higher energy level
When is the colour produced?
When they return to the ground state
What is the test for the ammonium ion?
Adding sodium hydroxide and warming the mixture
What dies this produce?
Ammonia
How can this be detected?
By using damp red litmus paper, which turns blue
