State two physical properties of noble gases and explain why noble gases are used in filament light bulbs rather than air.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Filament light bulbs contain a very hot tungsten wire that glows to produce light. Early bulbs used a vacuum, but modern bulbs are filled with a noble gas.
Model answer (4 marks)
Noble gases are monatomic gases with low boiling points, so they remain gaseous at room temperature and have very low density.
They are chemically inert, so they do not react with the hot tungsten filament. In contrast, air contains oxygen and nitrogen, which would oxidise the filament and cause it to burn away.
They are chemically inert, so they do not react with the hot tungsten filament. In contrast, air contains oxygen and nitrogen, which would oxidise the filament and cause it to burn away.
Examiner tips
- Use the exact terms ‘monatomic’, ‘low boiling point’, ‘inert’ and ‘oxidise’
- Show the contrast with air by mentioning oxygen/nitrogen
Common mistakes
- Confusing density with boiling point, or vice versa
- Failing to mention the inertness of noble gases or the oxidising effect of air
Mark scheme (4 marks)
- Noble gases have low boiling points / exist as gases at room temperature
- Noble gases have low density / are monatomic
- Noble gases are chemically unreactive / inert, so they do not react with the hot tungsten filament
- Air contains oxygen / nitrogen which would react with / oxidise the hot filament, causing it to burn away / break
Key terms in this question
Related
- All Cambridge International IGCSE Chemistry (0620) revision notes →
- How to answer a "State / Explain" question →
- Decode the mark scheme abbreviations →