Chamelon Chemistry Demonstration

Dec 8, 2023

Ignis

Chungnam Samsung Academy

Ignis chemistry club members prepared a chameleon chemical reaction experiment at Chungnam Samsung High School, South Korea. The experiment, called the chameleon reaction experiment, was expanded to observe the color change caused by the change in the oxidation number of manganese and the reaction rate due to the difference in the concentration of the solution as the subject of the experiment. It is a visually enjoyable experiment that is enjoyable to conduct.

Below are the the concepts needed to understand the experimental procedure.

Electrical negativity: A numerical value that indicates the degree to which an atom attracts electrons in a molecule. Electrons are attracted to the side where the electronegativity between different atoms is higher. Because of the different attraction to the atomic shared electron pair, the shared electron pair is pulled toward the atom where the stronger attraction acts.

Oxidation number: Oxidation number refers to the number of charges that a particular atom of a substance has when it is assumed that the exchange of electrons has occurred within a substance. Additionally, oxidation number is a method used to determine the flow of electrons in redox reactions, but it does not necessarily match the actual amount of charge that atoms in a particular substance has.

Oxidation: A reaction in which a substance combines with oxygen or loses hydrogen. The most common definition is response to losing electrons. It is a reaction in which the oxidation number increases, and it is an exothermic reaction in which heat is generated as the reaction occurs.

Reduction: In a chemical reaction, reduction means obtaining hydrogen or losing oxygen, and in a broad sense, obtaining electrons. It is a reaction in which the oxidation number decreases.

Rate of reaction: Rate of reaction refers to the rate at which a chemical reaction takes place. The reaction rate in a solution is expressed by measuring the concentration of a reactant or product over a certain period of time. The reaction rate is influenced by various variables and may be measured using the change in the concentration of chemicals per unit time. Temperature and physical conditions are factors that have a great influence on the reaction rate. Methods of increasing the reaction rate include increasing the concentration, increasing the temperature, mixing the solution well, increasing the surface area, and using a catalyst.

Experimental materials

Instruments: 50mL beaker*3, 250mL beaker*3, magnetic bar*3, stirrer, glass rod*3, medicine paper, medicine spoon*3, electronic scale, 250mL calibration cylinder, micropipette

MSDS

1. Sodium hydroxide

- Chemical formula: NaOH

- Materiality: Solid

- Molecular weight: 40

- Conditions to avoid: Heat

- Conditions to be aware of: Do not touch the skin, close the lid of the reagent after use because it is highly degradable.

- pH: 14 (20°C concentration 50g/L)

2. Potassium manganizate

- Formula: KMnO4

- Materiality: Solid

- Molecular weight: 158.034

- Conditions to avoid: Heat, Spark

- Conditions to watch out for: Avoid touching your skin

- pH: 8

Experimental process

1. After measuring 250 mL of distilled water accurately with a graduated cylinder, prepare it in a beaker.

2. Put 3g of NaOH(s) and 4.5g of sugar in a beaker.

3. Repeat the process 1 to 3 times to make 3 sugar-NaOH aqueous solutions.

4. After placing the beaker on the stirrer, add a magnetic bar so that the solution mixes well.

5. 0.01M KMnO4 solution is prepared by mixing 0.25mL of a 0.2M KMnO4 solution with 4.75mL of distilled water.

6. 0.005M KMnO4 solution is prepared by mixing 0.125mL of a 0.2M KMnO4 solution with 4.875mL of distilled water.

7. 0.002M KMnO4 solution is prepared by mixing 0.05mL of a 0.2M KMnO4 solution with 4.95mL of distilled water.

8. After adding each KMnO4 solution to the mixture of sugar and NaOH, observe the color change and the reaction rate at which the color of the solution changes.

Results

Color change of solution according to oxidation number change of Mn


Purple	Blue	Green	Yellow	Orange

the change in reaction rate due to the concentration of the solution

	Purple	Blue	Green	Yellow	Orange
0.01M	2.21s	2.80s	8.61s	29.62s	47.05s
0.002M	1.94s	2.58s	4.35s	38.60s	55.16s
0.005M	1s	2.14s	2.90s	38.83s	69.90s

Changes in oxidation number of manganese

1)MnO4 - Mn has an oxidation number of +7.

2)The oxidation number of Mn changes by receiving electrons from sugar.

MnO4 -(aq)+e- → MnO4 2-(aq)

3)MnO4 2- and Mn have an oxidation number of +6 when the solution turns green.

4)The color change appears as the manganese acid ion is changed from the manganese acid ion to the manganese acid ion.

MnO4 2-(aq)+2H2O(l)+2e- → MnO4 2-(s)+4OH-

5)When the solution turns yellow, it receives electrons to form manganese dioxide.

* KMnO4 (Purple) → K2MnO4 (green) → MnO2 (yellow)

+7	KMnO4	Purple
+6	K2MnO4	Blue
+5	K3MnO4	Green
+4	MnO2	Yellow

Reaction mechanism

1) Potassium permanganizate is reduced (got electrons) and sugar is oxidized (lost electrons).

2) Permanganate ion (purple) is reduced to form manganate ion (green)

• MnO4-(aq) + e- → MnO42-(aq)

3) Both purple permanganate and green manganate are present in the solution.

4) The permanganate and the manganate are mixed to form a blue solution.

5) After the reaction, more manganate of green color is produced, resulting in a green solution.

6) Green manganate ions are reduced to form manganese dioxide.

• MnO42-(aq) + 2 H2O(l) + 2 e- → MnO2(s) + 4 OH-

7) Manganese dioxide, a golden brown solid, is formed, but the particles are small and the color of the solution seems to change.

8) The particles of manganese dioxide are precipitated from the solution, and the solution becomes transparent.

The reaction rate according to the concentration of the solution

The reaction rate that changes as the concentration of the solution changes was observed by varying the concentration of each KMnO4 solution. There was no significant difference in the reaction rates of the three solutions at the beginning of the reaction, 0.01M, 0.005M, and 0.002M, but after the reaction proceeded to some extent, it was confirmed that the reaction rate increased in the order of 0.01M, 0.005M, and 0.002M. Therefore, it can be concluded that the higher the concentration of the solution, the faster the reaction rate.

Why we used potassium permanganizate

Manganese acid is a strong oxidizing agent and has a variety of colors. It is characterized in that it changes to purple, green (Mn2+), and brown (MnO4-) depending on the chemical reaction and the presence or absence of oxygen. In addition, it was used because it is a material with high stability in general.

Why we used sodium hydroxide and sugar

The reaction proceeds under alkaline conditions under the influence of a reducing agent. Sodium hydroxide, potassium hydroxide, ammonium hydroxide, etc. can be used to alkalize the permanganate solution, and various reducing agents can be used, but sugar is generally used.

Effect of concentration on reaction rate

The reaction speed generally increases as the concentration of the reactants increases. As the concentration of the reactants increases, the number of particles present in the unit volume increases, so the distance between the particles increases. Therefore, if the particles have the same average motion speed, the time it takes for the particles to collide with each other becomes shorter, so the number of collisions per unit time increases. The reaction speed increases because the number of particles that can react increases as the number of collisions of particles increases.

References

admin. (2017). 산화수 [oxidation number, 酸化數] | 과학문화포털 사이언스올. Scienceall.com. https://www.scienceall.com/%ec%82%b0%ed%99%94%ec%88%98-oxidation-number-%e9%85%b8%e5%8c%96%e6%95%b8/?term_slug=

‌ admin. (2018). 산화(oxidation) | 과학문화포털 사이언스올. Scienceall.com. https://www.scienceall.com/%ec%82%b0%ed%99%94oxidation-2/?term_slug=&sa_term=scidictionary

Chamelon Chemistry Demonstration

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