Testing for Gases
The Test for Carbon Dioxide Gas, CO2(g).
1) Carbon dioxide gas has no colour or smell.
2) Carbon dioxide gas will put out a lit splint.
dioxide gas will turn moist
from blue to red,
and moist universal indicator paper to yellow.
Carbon dioxide dissolved in water forms carbonic acid (H2CO3).
Carbonic acid is a weak acid (see the carbon cycle).
Specific Test for Carbon Dioxide Gas.
Carbon dioxide will turn lime water 'milky' or cloudy.
water is a solution of
calcium hydroxide (slaked
When carbon dioxide is bubbled through it,
a solid precipitate of calcium carbonate is formed.
Calcium carbonate is chalk or limestone,
and it is this that makes the lime water cloudy.
hydroxide + carbon dioxide calcium carbonate +
Ca(OH)2(aq) + CO2(g) CaCO3(s) + H2O(l)
Collecting Carbon Dioxide Gas.
dioxide gas is more dense than air
and can be
collected by downward delivery or using a gas syringe.
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