Chemicals:
| 0.2 M aqueous benzoquinone solution (10.8 g / L H2O)
| | 0.2 M aqueous sodium disulfite solution (38 g / L H2O) | |
The solution of benzoquinone should be prepared immediately before the demonstration, because it decomposes rapidly.
Glass wares:
| gas collecting cylinder 150 mL
| | 2 beakers 50 mL
| | glass stirring rod | |
Hazards and safety precautions:
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Benzoquinone is highly toxic. May be fatal if swallowed, inhaled or absorbed through skin. Severe irritant.
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Sodium disulfite may cause irritation and may be harmful if swallowed. May cause allergic reaction, skin and eye irritant.
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Safety glasses, protective gloves, effective ventilation! The p-benzoquinone solution should be prepared inside a fumehood!
Experimental procedure:
20 mL of aqueous Na2S2O5 solution are added to a collecting cylinder filled with 130 mL of freshly
prepared aqueous benzoquinone solution. After the reaction mixture has turned dark 20 mL of Na2S2O5
solution are added again.
Result:
A felt of needle-shaped dark crystalls is formed. The crystals are re-dissolved upon further addition of disulfite solution.
Video clip (Download RealPlayer .rm file)
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