GCSE OCR Gateway
C4:2c-e Flame Tests
for Cations
Learning Objectives:
C4.2c To describe
how to perform a flame test.
C4.2d To identify a
species from its test results.
C4.2e To interpret
flame tests to identify the ions of lithium (Li+), sodium (Na+),
potassium (K+), calcium (Ca2+) and copper (Cu2+).
How do you perform a flame test?
Flame tests are the
best. Why? Because you get to burn
stuff!!
Albeit not a great deal of
stuff but nevertheless, you get to burn stuff in a Bunsen burner.
Here’s how:
1.
Take a watch–glass
and add a small volume of concentrated hydrochloric acid to it.
2.
Take a
nichrome wire attached to a metal or glass rod.
The wire ought to have a small loop on the end.
3.
Put the wire
in the acid and then in a non-luminous Bunsen flame. Look for any colour in the colourless
flame. If it is coloured, the wire is
still contaminated.
4.
Repeat the
process using the acid till the wire is fairly free of contamination.
5.
Now you have a
clean nichrome wire.
6.
Take a small
sample of a solid metal chloride, say lithium chloride.
7.
Dip the wire
into the acid, into the chloride and then into the flame.
8.
The chloride
vaporises and the lithium ions colour the colourless luminous flame.
9.
You have
observed the flame colour of lithium!!
Repeat
using clean hydrochloric acid and a different metal chloride.
Here is a graphic of as
many flame colours as you are ever going to need from those great people at
Compoundchem.com
You can see the colours of
the metal ions you need for the GCSE course
Metal ion
|
Sodium Na+
|
Lithium Li+
|
Copper Cu2+
|
Calcium Ca2+
|
Potassium K+
|
Flame colour
|
Orange yellow
|
red
|
blue
|
Orange red
|
lilac
|
How do flame colours form?
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