Module 8: Applying Chemical Ideas Flashcards
What is a flame test and method?
Flame tests test for presence of metals or metal cations in samples.
Requires Bunsen burner, platinum wire, HCl and solid or aqueous solution of a salt containing metal ion.
1. Bunsen Burner on blue flame
2. Dip platinum wire in HCL to clean it.
3. Dip platinum wire into salt.
4. Place wire into flame.
How do flame tests work?
When the platinum wire is put in flame, the electrons in the element absorb the heat energy, causing the electrons to jump from their stable ground state to a higher energy level, in an ‘excited’ state. Electrons can move up multiple orbitals. However, the electrons will quickly fall back down to their stable ground state, emitting the energy they don’t need anymore in the form of light. Different energies of light correspond to different colour, thus, as every element has a different electron configuration, they emit different light.
Light energy = Higher energy level - original energy level
Positive Flame Test results
Limitations of flame tests?
Some metals don’t produce colours e.g. Gold, Silver, Magnesium
Some metals are unsafe to test, e.g. Lead.
It can be difficult to distinguish between some metal ion colours due to similar colours e.g. Calcium, Lithium and Strontium all produce reddish flames.
Precipitation Tests for Individual metal cations
Aluminium and Magnesium both produce white precipitates after NaOH is added, to differentiate keep adding excess and the aluminium will eventually dissolve to be colourless.
Precipitation Tests for multiple metal cations
What is a complexation reaction?
A reaction in which complex ions are formed, when one or more small molecules, called ligands, attach themselves to a cation. Complex ions often exist in vibrantly coloured states, and are thus easily identified.
What is a ligand and common ones?
Common ligands:
Water
Ammonia
Chloride
Hydroxide
How to test for carboxylic acid?
React with metal/hydrogen carbonate to produce CO2 gas.
Precipitation test for anion
What is colorimetry?
Technique that relies on the absorbance of coloured light to determine the concentration of coloured ions in a sample.
Absorbance formula?
