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The Red-White-and-Blue Demonstration

Last updated

Feb 23, 2023
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- The Reaction Between Magnesium and CO₂
- The Relative Activity of Metals

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Chemical Concepts Demonstrated

Kinetics
Multi-step reactions

Demonstration

Three solutions are combined in alphabetical order.

Solution A: Na₂SO₃ * H₂O dissolved in water mixed with 2,4,2',4',4"-pentamethoxytriphenyl methanol dissolved in acetone.
Solution B: Cd(NO₃)₂ * H₂O and HCl added to water, shaken, and diluted.
Solution C: NaIO₄ dissolved in water.

Observations

Solutions A and B produce a red solution. Adding solution C after this turns the solution milky white, then blue after a time.

Explanations (including important chemical equations)

The hydrochloric acid in solution B turns the 2,4,2',4',4"-pentamethoxytriphenyl methanol (an indicator) red. The addition of solution C causes the pH to increase due to the formation of OH^-ions in the IO₄^- oxidation of S₂O₃²^-.

2 S₂O₃²^- (aq) + IO₄^- (aq) + H₂O (l) --> S₄O₆²^- (aq) + IO₃^- (aq) + 2 OH^-(aq)

When the indicator turns colorless again, the milky-white suspension of Cd(IO₄)²⁺ becomes apparent. The further increase in pH triggers another indicator (thymolphthalein), turning the solution blue.

Contributors

Dr. George Bodner (Perdue University)

Chemical Concepts Demonstrated

Demonstration

Observations

Explanations (including important chemical equations)

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