Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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potassium nitrite : KNO2
sodium sulfite : Na2SO3
sulphuric acid : H2SO4
sodium chloride : NaCl
hydrochloric acid : HCl
sodium chlorate : NaClO3
Class:
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elem=Cl
redox
Summary:
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Sodium chlorate reacts with chloride in acidic environment, forming chlorine
(which can be detected by means of its odour) and a fairly intensely colored
yellow gas (chlorine dioxide). The color of this gas is much more intense
than the color of chlorine.
The yellow compound is destroyed by sulfite and nitrite.
Description:
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Sequence 1:
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Add some concentrated HCl (appr. 30% by weight) to some solid NaClO3: The
solid dissolves and starts bubbling. The liquid starts foaming a little bit.
The liquid becomes intense yellow and an intensely colored yellow gas is
formed. After the reaction there is an intense yellow liquid and the test
tube is filled with the intensely colored yellow gas.
Add a lot of water to the test tube slowly: The gas is driven out of the
test tube and when it leaves the test tube, it can be seen to go downwards.
It is much more dense than air. Even when diluted more than 10 times, the
liquid still has a fairly intense yellow color.
Take a little part of the diluted yellow liquid and add an excess amount
of sodium sulfite: The solid dissolves and the liquid becomes colorless.
The smell of SO2 can be observed, but some other smell can be observed as
well. The pure smell of SO2 is different.
Sequence 2:
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Mix some solid NaCl and NaClO3 and add some dilute H2SO4 (appr. 2 mol/l):
Part of the solid dissolves (it is not clear what dissolves first). The
liquid becomes colorless and clear and some solid remains undissolved.
Heat the liquid with the little amount of remaining solid: The liquid turns
intense yellow and a yellow gas is produced. At the remaining solid, gas
bubbles are formed.
Add some solid potassium nitrite and quickly cap the test tube with a
rubber stopper and shake well: At first, the color of the gas mixture
changes from yellow to pale brown, but quickly the gas mixture becomes
colorless and the liquid becomes colorless. Nitrite quickly reacts with
the intensely yellow-colored compound.
Put the capped test tube upside down under water and remove the rubber cap:
Water is sucked into the test tube. The volume of water, sucked into the
test tube, is approximately 20% of the total volume of the gas mixture in
the test tube.