Peroxide Volcanoes in the Classroom

Peroxide Volcano

These experiments involve the use of peroxide of various concentrations, detergent and various organic and inorganic catalysts. The reaction essentially involves speeding up the natural decomposition of hydrogen peroxide into oxygen and water, according to the following equation:

2H2O2(l) --> 2H2O (l) + O2(g)

What is a Catalyst?

A catalyst is any substance that affects the rate of a chemical reaction. Most catalysts chemists are interested in are those that speed up reactions. They manage to do this by lowering the "activation energy" required to set the reaction in motion. This can be brought about by creating an alternate chemical pathway that requires less energy or by providing a surface or substrate that allows the reactant molecules to collide with each other more easily.

In the case of the decomposition of hydrogen peroxide, various catalyst can lower the required activation energy. Inorganic catalysts composed of compounds of the transition metals can be very effective in this regard. These include powdered manganese dioxide, potassium iodide, potassium sulphate and iron oxide. Organic catalysts such as yeasts, liver, blood and potatoes can also produce a similar, although often less spectacular, result. This is because they contain enzymes called "peroxidases" (or catalases) that naturally decompose hydrogen peroxide.

Making a Child-Friendly Peroxide Volcano – Materials and Teaching Method

The use of a lower strength peroxide solution and an organic catalyst may be a safer alternative for a primary classroom or for teachers with less science experience than others. This could involve a 3-6% hydrogen peroxide solution and the use of activated yeast as a catalyst for the decomposition reaction.

The following materials and equipment are required:

•                250ml plastic bottle (this could be modified to look like the cone of a volcano using papier mache or plasticine)

•                ½ cup 3% hydrogen peroxide solution

•                1 packet of active (live) yeast

•                ¼ cup detergent

•                warm water

•                food colouring

•                safety goggles

Students should be instructed to copy down the following directions, which could be followed by a teacher-led explanation.

•                Wearing safety goggles, add the hydrogen peroxide, detergent and food colouring to the plastic bottle. Mix these ingredients together by swirling the bottle. Place the bottle in a sink.

•                Mix the packet of active yeast with a small amount of warm water and allow to stand for around 5 minutes. This helps to activate the yeast cells.

•                Pour the yeast mixture into the plastic bottle and watch the results!

Note that the detergent is used to create a more spectacular foaming effect, as it combines with the bubbles of oxygen that are produced.

The following questions could be written on the board after students write up the experiment and their observations:

1.             What ingredient in this experiment acted as a catalyst to speed up the decomposition of hydrogen peroxide?

2.             Why was the packet of active yeast mixed with warm water?

Making a Heavier Duty Peroxide Volcano- Materials and Teaching Method

For a more dramatic display, 30% peroxide solution is used, with a transition metal compound acting as the catalyst. In this example, potassium iodide powder is added, but it could also be in the form of a saturated solution. Note that 30% hydroxide solution can cause burns and eye damage. In addition, adding too much potassium iodide can result in an over-vigorous reaction that may spray over everyone in the room.

The following materials and equipment are required:

•                50 mL 30% hydrogen peroxide

•                1 teaspoon potassium iodide powder

•                10ml detergent

•                food colouring

•                500ml glass measuring cylinder

•                safety goggles

•                rubber gloves

•                matches and wooden splint

Students should be instructed to copy down the following directions, which could be followed by a teacher-led explanation.

•                Put on the safety goggles and gloves.

•                Place the measuring cylinder on a large sheet of newspaper or plastic.

•                Add the hydrogen peroxide and detergent to the cylinder.

•                Squirt a small amount of food colouring down the inside wall of the measuring cylinder.

•                Add the potassium iodide and stand back.

Students should notice large volumes of coloured, foamy detergent pouring out of the cylinder. The teacher could demonstrate that the bubbles are oxygen gas by placing a glowing wooden splint inside the cylinder. The splint should re-light in the presence of such a large volume of oxygen. In addition, the teacher should indicate that this decomposition reaction is exothermic, meaning that heat is produced as a by -product.

The following questions could be written on the board after students write up the experiment and their observations. Note that potassium iodide, as with all catalysts, is not a reactant and therefore not consumed in the reaction.

1.             Write the equation for the decomposition of hydrogen peroxide.

2.             Why isn’t potassium iodide included in the above reaction?

3.             Explain why the glowing splint re-ignited when placed in the measuring cylinder.

4.             Is this reaction exothermic or endothermic? Explain.

Peroxide Volcano Follow -Up Activities

This reaction can be repeated without using detergent. When carried out in a 250ml plastic bottle it results in greyish steam shooting out of the container. This could be used to model the hot steam and ash that emanates from some volcanoes.

The demonstration can also be turned into a controlled experiment by varying the concentration of peroxide used or the type or amount of catalyst added. An interesting experiment designed by the Royal Society of Chemistry compares the rate of production of oxygen bubbles produced using metallic compounds, liver and potato as catalysts for the decomposition reaction.

Students should conclude from these activities that hydrogen peroxide decomposition is rapidly accelerated in the presence of inorganic or organic catalysts, producing large amounts of heat and oxygen gas. The catalysts, themselves, however, are not consumed in the reaction.

References

The Royal Society of Chemistry, "Catalysts for the Decomposition of Hydrogen Peroxide," rsc.org

Using Hydrogen Peroxide.com, 2007.

Woodrow Wilson Leadership Program in Chemistry, "The Effect of a Catalyst on the Rate of a Reaction," woodrow.org, 1986.

Woodrow Wilson National Fellowship Foundation, "Comparison of the Effects of Inorganic Catalysts and Enzymes on Peroxide Decomposition," woodrow.org, 1988.

Comparing Oil Viscosity in the Classroom

Fig.1 - Comparing Viscosity Using Air Bubbles

Viscosity is defined as a fluid’s internal resistance to flow. The correct amount of viscosity is important in oils used as lubricants. Motor oils, for instance, will not prevent friction between the engine parts if they are too thin but, conversely, will not allow parts to move freely if they are too viscous. Heat reduces the viscosity of a liquid and must therefore be taken into account when selecting appropriate oils.

The viscosity of fluids can be gauged by simply observing how easily they pour or spread along a solid surface or by determining the time taken for an object to move vertically through it. The following experiments are suitable for a middle secondary class, with methods ranging from simple to moderately difficult.

A Simple Method for Comparing the Viscosity of Oils – Materials and Teaching Method

In this experiment the viscosity of different oils is compared by determining the time taken for air bubbles to rise to the top of an inverted container of the oil (as demonstrated in figure 1).

Fig. 2- Determining the Viscosity of Engine Oil

The following materials and equipment are required per group of around 4 students:

•                four empty 500ml clear plastic drink bottles

•                200ml of each of the following: olive oil, canola oil, low viscosity motor oil, high viscosity motor oil

•                stopwatch

Students should be instructed to copy down the following directions, which could be followed by a teacher-led explanation.

1.             Pour each of the four oils into the clear plastic bottles and screw on the lids.

2.             For each oil, turn the bottle upside down and time how long it takes for an observed air bubble to reach the top of the fluid.

3.             Repeat this procedure twice and obtain an average for each oil.

4.             Record results in a table and draw a column graph of oil type v. average time for bubbles to rise.

Viscosity Follow-Up Activity

This experiment could be repeated after standing the four bottles of oil in a water bath or container of hot water for around 5 minutes. Students should observe that the viscosity of each oil decreases with increasing temperature. An alternative, yet still simple, experiment could involve timing how long each type of oil takes to actually pour out of the bottle when the lid is removed and it is turned upside down (see a similar method in figure 2).

A More Involved Method for Comparing the Viscosity of Oils – Materials and Teaching Method

This method, which involves calculating the time taken for a ball bearing to reach the bottom of a vertical column of the oil, can be used to actually calculate the numerical value for the viscosity,η, of each type of oil, in g/cm.s.

Data needed for this calculation include the radius and density of the ball bearing, the density of the oil and the speed of the ball bearing as it moves through the fluid. Alternatively, students may choose to simply compare the time taken for the ball bearing to travel through each type of oil.

The following materials and equipment are required per group of around 4 students:

•                four one litre measuring cylinders

•                one litre of each of the following: olive oil, canola oil, low viscosity motor oil , high viscosity motor oil

•                stopwatch

•                electronic balance

•                twelve ball bearings, each 3mm in diameter

•                10ml measuring cylinder of water to measure volume of the ball bearing by displacement

Students should be instructed to copy down the following directions, which could be followed by a teacher-led explanation.

1.             Pour each of the four oils into the measuring cylinders.

2.             Using the electronic balance and the measuring cylinder of water for the ball bearing, determine the density of the ball bearing and the oils by dividing their mass by their volume. The results should be in g/cm3.

3.             Calculate the density of the oil by dividing its mass by its volume.

4.             Drop a ball bearing into each of the four types of oil and record the time in seconds it takes to reach the bottom of the cylinder.

5.             Repeat this procedure twice and obtain an average for each oil.

6.             Measure the distance travelled by the ball bearing in cm and divide this distance by the average time taken in order to determine the average velocity (in cm/s) of the ball bearings in each cylinder.

7.             Record all results in a table.

Students can use the following equation, derived from Stokes’ Law, to determine the viscosity, η, of each type of oil in g/cm.s:

Viscosity (η) =2(Δρ)gr2 / 9v,

where Δρ is the density difference between the oil and the ball bearing, g is acceleration due to gravity of 980cm/s2, r is the radius of the ball bearing and v is the average velocity of the ball bearing.

Follow-Up Activity: Motor Oil Viscosity and Temperature

A good motor oil will not change markedly over a wide range of temperatures, as this could affect engine wear and tear. The above experiment could be repeated by standing the measuring cylinders in water baths that have been adjusted to specified temperatures.

Further work could involve students researching Stokes’ law, fluid dynamics and terminal velocity.The ball bearings should have reached a constant, or 'terminal' velocity when the force of gravity became balanced by buoyancy and viscosity forces within the oils.

References

Olsen, Andrew. " The Viscosity of Motor Oil." Science Buddies Science Fair Projects, 2010.

The Nuffield Foundation. "Falling Through a High Viscosity Liquid." Practical Physics, 2004.

Brine Shrimp Experiment: Testing the Effect of pH

Figure 1 - Artemia monica from Mono Lake

Brine shrimp, Artemia ( figure 1), belong to the class Crustacea, along with prawns, lobsters, crayfish and yabbies. Also known as 'sea monkeys', they thrive in inland lakes and salt pans that have salt concentrations of up to 25%. A slightly alkaline pH is also required for their survival. In the USA the Great Salt Lake (figure 2), Mono Lake and San Francisco Bay are good sources of Artemia. In Australia, a related species, Parartemis, thrives in saline lakes.

In these salty conditions, brine shrimp have few predators, coupled with an abundant supply of algae to feed on. Brine shrimp eggs (cysts) can remain dormant for years if left dry. When conditions of temperature, salinity and pH become suitable, these cysts hatch to form larvae, or "nauplii." The total life cycle span for Artemia is around one year.

Male brine shrimp are identified by the large pair of "graspers" on their heads. Live brine shrimp or their eggs are harvested for use as tropical fish food in the aquarium and aquaculture industries.

The Effect of pH on Brine Shrimp – Materials and Teaching Method

Figure 2 - Great Salt Lake, Utah

A simple definition for pH is that it describes the acidity, or hydrogen ion concentration, of a solution. Specifically, a solution’s pH is equal to minus the log base 10 of its hydrogen ion concentration , so a high pH indicates low acidity, or alkaline conditions, and a low pH indicates high acidity. Universal indicator paper can be used in this activity to estimate the pH of the various solutions tested.

The following materials and equipment are required per group of around four students:

•                non-iodised table salt

•                sodium carbonate

•                vinegar

•                three large test tubes

•                magnifying glass or stereo microscope

•                three 250ml beakers

•                teaspoon

•                universal indicator paper and colour chart

Students should be instructed to copy down the following directions after a teacher-led explanation.

•                Pour 200ml water into each of three beakers. Label these beakers "1," "2" and "3."

•                Add 1 teaspoon salt to each beaker.

•                Add 1/4 tsp sodium carbonate to beaker 2.

•                Add 1/4 teaspoon vinegar to beaker 3.

•                Pour equal amounts of liquid from these beakers into three large test tubes, also labelled "1," "2" and "3."

•                Drop a piece of indicator paper into each test tube and record the pH of each. Determine whether the liquid in each tube is acidic, basic or neutral.

•                Cover the surface of the liquid in each of the tubes sparingly with brine shrimp eggs. Leave the test tubes in a warm place for 24 hours.

•                Observe, count and draw any brine shrimps as they hatch over the next few days.

Students should record their results in a table. Columns could be labelled "pH of test tube," while the rows could be headed "Number of brine shrimp hatched: Day 1, Day 2, Day 3 etc." Hatching rates should be more successful in the alkaline test tube (i.e. tube 2).

Brine shrimp could be observed under a magnifying glass or stereo microscope and then drawn and labelled (see figure 1). Students may also observe their locomotion and investigate how they respond to a light source such as a torch.

The following questions can be written on the board after students write up the experiment and their observations:

1.             Draw a diagram of one or more of your brine shrimps. Try to identify them as male or female.

2.             What do you think is the optimum pH for the growth of brine shrimp?

3.             Describe the swimming motion of brine shrimp.

4.             Use resource material to find out whether brine shrimp reproduce sexually, asexually or if they reproduce using both methods.

5.             How do brine shrimp respond to a light source such as a torch or microscope lamp?

Brine Shrimp Follow-Up Activities

Further experiments could be designed to test the effects of pollution, temperature and salt concentration on Artemia hatching rates. As in all controlled experiments, all variables except for the one being tested must be kept constant. In other words, if temperature is being tested, the other variables such as volumes, pH and salt concentrations must be kept the same for each test tube.

If students wish to keep the brine shrimp for an extended period they can feed them with small amounts of dried yeast or Spirulina algae (available from pet shops). They should ensure that the water is changed regularly and replaced with appropriate amounts of salt and sodium carbonate.

References

Brine Shrimp Direct, 2010,'Brine shrimp in the Classroom', brineshrimpdirect.com

Science Netlinks, 2001, 'Brine shrimp 2: Brine Shrimp Survival', sciencenetlinks.com