Wednesday 1 March 2017

GCSE OCR Gateway C4:2c-e Flame Tests for Cations

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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