Chemical Volcano

Author(s): Miha Lee
Instrumentation - Teacher's Guide
SED 695B

Overview:

This is a rapid oxidation of glycerin by potassium permanganate. Glycerin is a kind of alcohol, and potassium permanganate is a strong oxidizing agent. The reaction between these two reactants occurs almost instantaneously and very dramatically with lots of smoke and fire erupting from their mixture. This reaction can be applied to demonstrate an exothermic reaction and the effect of surface area on reaction rate.

Topics

  1. Oxidation of Alcohol
  2. The Effect of Surface Area on the Reaction Rate
  3. Exothermic Reaction

Standards: Chemistry - Grades Nine Through Twelve
Science Content Standards.

  • 3g.Students know how to identify reactions that involve oxidation and reduction and how to balance oxidation-reduction reactions.
  • 7b.Students know chemical processes can either release (exothermic) or absorb (endothermic) thermal energy.
  • 8b. Students know how reaction rates depend on such factors as concentration, temperature, and pressure.
  • 10e.Students know how to identify the functional groups that form the basis of alcohols, ketones, ethers, amines, esters, aldehydes, and organic acids.

 

Experiment Summary

As the glycerin comes in contact with the potassium permanganate, the oxidizing properties of the permanganate ion come into play with the glycerin. The oxidation of the glycerin is very exothermic and after a few seconds the released heat causes the glycerin to also ignite and burst into flame and release smoke. After adding glycerin to the dish, immediately step back because spark and solid potassium permanganate will be expelled from the dish.

14KMnO4(s) + 4 C3H5(OH)3(l)      7K2CO3(s)

+ 7Mn2O3(s) + 5CO2(g) + 16H2O(g)

Material and Procedure

Material:

  • 5mL of glycerin
  • 40 g of potassium permanganate (KMnO4)
  • 1 evaporating dish
  • Spoid
  • Goggles
  • Gloves
  • A safety shield

Procedure I : Oxidation Reaction and Combustion of Glycerin

1.      Wear goggles and gloves and place a safety shield between the students and the reaction vessel.

2.      Place about 15g of crystal potassium permanganate (KMnO4) into a clean evaporation dish.

3.      Set a stopwatch to measure a time that is taken by the oxidation to begin.

4.      Pour about 1mL, enough to moisten the surface, of glycerin into the middle of the pile of potassium permanganate. Immediately set the stopwatch and stand back.

5.      The reaction will begin to smoke and then burst into flames within a few minutes. It will occur almost instantaneously for very fine crystals.

 Procedure II : The Effect of Surface Area on the Reaction Rate

6.      Grind crystals up to fine powder in a clean and dry mortar and pestle.

7.  Repeat the same process from the step 1 to the step 5.

8.  Compare the times that were taken by the oxidation to begin.

 

Questions and Applications to Everyday Life

Questions:

1.      What type of reaction is this?  => Oxidation-reduction reaction.

2.      What observable evidence indicates that a chemical reaction is taking place? => fire, smoke, color change

3.      What substance is oxidized in this reaction? => glycerin

4.      What is the oxidant in this reaction? => potassium permanganate

5.      Why does the reaction rate depend on the size of potassium permanganate crystal? => The sizes of the crystal affect the frequency of collision between reactants. The finer the crystals are, the greater the surface area; the greater the surface area, the faster the reaction occurs.

6.      Is this reaction exothermic or endothermic? => Heat is liberated, so the reaction is exothermic.

Applications to everyday life:

1. Exothermic Reaction => When we burn fuels in our car's engine or heater of our home, we use the heat generated from the combustion reactions. The absolute amount of energy in a chemical system is extremely difficult to measure or calculate. The enthalpy change, ΔH, of a chemical reaction is much easier to measure and calculate. A bomb calorimeter is very suitable for measuring the energy change, ΔH, of a reaction.

2. Oxidation of Alcohol => When we produce ketones, aldehydes and carboxylic acids, we oxidize alcohols.

3. Surface Area Effect on Reaction Rate

  • We chew foods to facilitate digestion and absorption of nutrition.
  • We try to vaporize the fuels in oder to mix well with oxygen so that their combustion can be faster.
  • Cell size is very small even in the large animals to ensure the speed of exchange of metabolism.

 

Photos and Descriptions

1.      Potassium permanganate: KMnO4

  • also known as permanganate of potash
  •   prismatic purple-black glistening crystal
  •   a strong oxidizing agent because of manganese ion in the +7 oxidation state
  •   dissolves in water to give deep purple solutions
  •   used as a disinfectant and a propellant in rocket

2. Glycerin: 1,2,3-propanetriol

  • also called glycerol
  •   Molecular formula HOCH2CH(OH)CH2OH
  •   colorless, odorless, viscous liquid
  •   widely used in soaps, cosmetics, and  a sugar substitute
  •   three hydrophilic alcoholic hydroxyl groups responsible for its solubility in water and its hygroscopic nature

 

3. Oxidation of Glycerin

A few drops of glycerin are placed into a hollow in a pile of potassium permanganate. Potassium permanganate is a strong oxidizing agent and glycerin is an easily oxidized substance. Consequently a redox type reaction is expected between these two substances. However, the product cannot be controlled in this reaction.

 

 

4.      Exothermic Reaction

In chemistry, an exothermic reaction is one that releases heat. In an exothermic reaction, the total energy absorbed in bond breaking is less than the total energy released in bond making. In other words, the energy needed for the reaction to occur is less than the total energy produced. As a result of this, the extra energy is released, usually in the form of heat.

   

 

5. Oxidation of Alcohol

The outcome of oxidation reactions of alcohols depends on the substituents on the carbinol carbon. In order for each oxidation step to occur, there must be H on the carbinol carbon. Primary alcohols can be oxidized to aldehydes or further to carboxylic acids. In aqueous media, the carboxylic acid is usually the major product. Secondary alcohols can be oxidized to ketones but no further. Tertiary alcohols cannot be oxidized.

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