Student Activity: Predators in Control

Predator–prey relationships are one of the most important biotic relationships in the sustainability of an ecosystem. Predators are the natural controls in an ecosystem, limiting the size of a prey population. Many studies have illustrated that the long-term sustainability of an ecosystem is severely affected if top predators are eliminated. Prey populations increase as a result of the loss of their natural predators and they overgraze the vegetation resulting in ecosystem collapse.

Top predators―including wolves, grizzly bears, sea otters, and alligators―are referred to as keystone species. They are crucial in maintaining and sustaining ecosystem function. For example, on the west coast of Canada the loss of sea otters, a keystone species, has led to an increase in populations of sea urchins and other shellfish which are overgrazing on the underwater kelp forests and destroying the habitat of many different organisms.

This game models the interrelated effects of predator (fox) and prey (rabbit) populations over several generations.

Click here to download complete demo….

Is there a place for 30% peroxide in High School Chemistry?

In a recent blog post, the activity Elephant’s Toothpaste was demonstrated. The activity was in keeping with our STAO safety policy regarding chemical use. In that policy, we suggest the use of small quantities of chemicals, at as low a concentration as possible to allow the reaction to proceed. Teachers are also asked to explore safer alternatives to replace reactions that introduce an unacceptable element of risk. In this video, it was suggested that the reaction proceed with 3 or 6% hydrogen peroxide, yeast as a source of catalase, soap and food colouring. As expected, the reaction proceeded well with a coloured soapy foam spilling out of the container. This was a good example of putting our policy (low concentrations, safer alternatives). As peroxide, even in low concentrations (6%), can cause serious damage to eyes, goggles should have been worn by the student in the video.

Hazards of 30% Hydrogen Peroxide

STAO recommends that 30 % hydrogen peroxide be only used by the teacher.  Its hazards include:

  • It can act as either an oxidyzing agent or reducing agent
  • It is caustic
  • It can decompose rapidly in the presence of catalysts
  • It can rapidly decompose when exposed to metal impurities (especially multivalent)
  • It can spontaneously ignite organic materials such as cotton, leather, paper towels

While these properties may seem alarming, they are common among the other oxidizers that are in our chemical inventory and used for lab activities and demonstrations. The “Teacher Use” designation should signify to teachers that the substance has a hazard level above the chemicals used for student activities. Precautions for the use of 30 % hydrogen peroxide include goggles, acid resist gloves, synthetic apron and keeping students at a safe distance from the demonstration. A self-standing chemical shield (aka explosion shield) is also reduces the risk injury without obscuring the view.

Recommended Video Resource 

Evonik Industries has produced a 30-minute training video (see link below) covering the industrial use of 50 -70% hydrogen peroxide. The video provides several neat demonstrations showing rapid decomposition, reaction to impurities and spontaneous combustion. It offers several good safety tips appropriate for high school. These include:

  • Never pour a decanted sample back into a stock bottle
  • Store peroxide at less than 30′ C
  • Store the stock bottle within a plastic tray
  • Use non-organic PPE’s (not leather)
  • Do not wipe spills with paper towels or natural cloths.
  • Even very dilute solutions can cause serious eye damage

 

Dave Gervais

Chair STAO Safety Committee

Resources 

1) H2O2 Safety Training Video – Evonik is a leading global manufacturer of hydrogen peroxide

Link to Video

2) Link to Picture of  Hydrogen Peroxide burns (35%)

 

 

 

 

 

Classification of Lasers Question to the STAO Safety Committee

laser 2Question:

The STAO Safe on Science document (2011) indicates that only class 1 and class 2 lasers are recommended for use in high school science classes. Many of the documents that I have examined indicate that Class 3A (old classification), now called Class 3R (new classification) are also safe, unless viewed through an optical device. I respectfully request that the safety committee re-examine this issue, and include Class 3R in the  recommendation.

Click for the committee’s response.