A filament lamp contains a thin tungsten wire that glows at about 2500 °C. The bulb is filled with a gas. Heavier gas atoms or molecules are better at slowing down the evaporation of the tungsten, so the filament lasts longer.
The table shows information about some gases that could be used.
| Gas | Relative atomic or formula mass | Reaction with hot tungsten | Percentage by volume in air | Relative cost |
|---|---|---|---|---|
| air | 29 (average) | oxygen reacts | not applicable | very low |
| nitrogen | 28 | none | 78.1 | low |
| argon | 40 | none | 0.93 | low |
| krypton | 84 | none | 0.0001 | high |
| xenon | 131 | none | 0.000009 | very high |
Explain why air is not used to fill filament lamps.
Use the data to explain why krypton is much more expensive than argon.
A krypton-filled lamp contains 36 cm3\mathrm{cm^{3}}cm3 of krypton, measured at room temperature and pressure. Calculate the mass of krypton in the lamp. Relative atomic mass: Kr = 84. One mole of any gas occupies 24 000 cm3\mathrm{cm^{3}}cm3 at room temperature and pressure.
A manufacturer wants to make a lamp that is cheap to produce but has a long-lasting filament. Evaluate the use of the gases in the table for filling this lamp.
38 exam-style questions on Edexcel GCSE Chemistry 7.3 Group 0, covering 7.3.1 The noble gases. Each one has a worked solution and a mark scheme showing where the marks go.