Teacher Demo/Student Activity: Powder Disaster

Introduction

Flour is an ingredient that is found in most kitchens and used regularly for baking and cooking.  Consequently, it is considered safe, and people do not regard the potential hazards.  In reality, flour and dust explosions are extremely dangerous, and reducing the risk of such an explosion is a major concern to the agriculture and food processing industries.

The purpose of this demonstration/activity is to illustrate the importance of being aware of potentially harmful situations and practices in the workplace. In particular, the dustiness of a material can affect the nature of chemical reaction, affecting a safe working environment.

How does it work?

Flour is combustible. When sitting as a stable pile the fuel (flour) is more connected to other flour particles than oxygen particles. As dust, each dust particle is surrounded by oxygen particles. This supports the combustion of the flour particle. As each particle moves through the flame, the combustion moves with the particles. Flour explosions tend to be connected to the movement of flour through air. The source of ignition is often discovered to be a static discharge.

 

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Freezing by Boiling Demo – Flinn Scientific

The boiling point of a liquid depends on the external air pressure. When water is placed under vacuum, the boiling point decreases and the water boils. Boiling, however, is an endothermic process—as the water boils, the temperature decreases, and the water soon freezes!

In this demo, pressure changes cause a sample of acetone freezes while still boiling.

Click here for the complete instructions, courtesy of Flinn Scientific 

Teacher Demo/Student Activity: Limit to Cell Size

41800307 - main blood cells in scale isolated on white background

41800307 – main blood cells in scale isolated on white background

Introduction 

Cells require a constant supply of glucose and oxygen to produce energy.  Cellular respiration occurs in the mitochondria of a cell. As a result of this process, large quantities of waste carbon dioxide must be expelled from the cell. All materials involved in this reaction are either imported or exported through the cell membrane by diffusion.

Students observe the effect of cell volume and surface area on the extent of diffusion of the sodium hydroxide solution through the “cell”.

teacher-demo-student-activity-limit-to-cell-size