downward delivery
suitable for heavy dense gas solubility not important e.g. chlorine,
upward delivery
suitable for light low density gas, solubility not important e.g hydrogen
C7.07 Methods for collecting gases
downward delivery
suitable for heavy dense gas solubility not important e.g.
chlorine,
upward delivery
suitable for light low density gas, solubility not important e.g
hydrogen
collection over
water
Suitable for any gas with a low solubility e.g. nitrogen
collection using a gas syringe
Suitable for any gas especially if volume is to be measured.
Learning activity - use the data in the table and the
rules above to select a collection method and give a reason.
| gas | relative density | water solubility | method | reason |
| air | 14.4 | low | X | X |
| oxygen | 16 | low | ||
| hydrogen | 1 | low | ||
| carbon dioxide | 22 | low | ||
| nitrogen | 14 | very low | ||
| ammonia | 8.5 | very high | ||
| methane | 8 | low | ||
| chlorine | 35.5 | high | ||
| sulfur dioxide | 32 | high | ||
| helium | 2 | very low |
C7.08 Testing for common gases
| Gas | test | positive result |
| hydrogen | light with burning splint | squeaky pop |
| oxygen | test with glowing splint | splint relights |
| ammonia | damp red litmus smell |
turns blue pungent |
| hydrogen chloride | damp blue litmus open ammonia bottle smell |
turns red white smoke above bottle sharp |
| carbon dioxide | bubble through limewater | limewater turns milky |
| sulfur dioxide | damp blue litmus damp dichromate paper smell |
turns red turns from orange to green sharp |
C7.09 Hazards with common gases
Hydrogen - flammable, explosive when mixed with air. Use in small
amounts.
Hydrogen chloride and sulphur dioxide- poisonous as they are very acidic.
Use small amounts and only in the fume cupboard.