CCEA A-Level Chemistry 1110
Formulae, Equations and Amounts of Substance
Atomic Structure
Bonding
Intermolecular Forces and Structure
Shapes of Molecules and Ions
Redox
The Halogens
Acid-Base Titrations
Qualitative Tests
Formulae and Amounts of a Substance
Nomenclature and Isomerism in Organic Chemistry
Alkanes
Alkenes
Halogenoalkanes
Alcohols
Infrared Spectroscopy
Energetics
Kinetics
Equilibrium
Group II Elements and Their Compounds
Lattice Enthalpy, Entropy and Free Energy
Rates of Reaction
Equilibrium and Acid-Base Equilibria
Isomerism
Aldehydes and Ketones
Carboxylic Acids
Derivatives of Carboxylic Acids
Aromatic Chemistry
Spectroscopy and Chromatography
Volumetric Analysis
Transition Metals
Electrode Potentials
Amines
Amides and Polymers
Amino Acids and Proteins
Qualitative Tests
Flame tests for metal cations
- 3 things to know
- Unit AS 1
Overview
How the nichrome wire is cleaned before a flame test, flame colour given by lithium ions and flame colour given by sodium ions.
What you need to know
Answer each one before you reveal it.
Why is concentrated hydrochloric acid used rather than water in a flame test?
Which part of the Bunsen flame is used for a flame test, and why?
Questions from this subtopic
Each one with the model answer underneath.
- 1
Why is nichrome wire used to carry out a flame test?
Model answer
Nichrome has a high melting point and gives no flame colour of its own, so it does not interfere with the result.
- 2
Describe how the nichrome wire is cleaned before a flame test.
Model answer
The wire is dipped in concentrated hydrochloric acid and held in a hot Bunsen flame, and this is repeated until the flame shows no colour.
- 3
Why must the wire be cleaned before every test?
Model answer
Traces of an earlier sample would give their own colour and could mask or be mistaken for the colour of the sample being tested.
- 4
Why is concentrated hydrochloric acid used rather than water in a flame test?
Model answer
The acid converts the metal compound into its chloride, which is more volatile and vaporises readily in the flame.
- 5
Which part of the Bunsen flame is used for a flame test, and why?
Model answer
The edge of the hot blue non-luminous flame is used, because a yellow luminous flame would obscure the colour produced.
- 6
Explain in terms of electrons why a metal ion gives a coloured flame.
Model answer
Heat energy promotes electrons to higher energy levels, and the light of a characteristic colour is emitted as those electrons fall back down.
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