Two translucent liquids are mixed. At first, nothing happens: the resulting solution is still translucent. Suddenly, with no warning, the solution turns blue-black all at once.

Curriculum links include redox reactions, rate of reaction, kinetics

The enzyme lactase is widely used in the dairy industry to convert the naturally occurring disaccharide sugar lactose into glucose and galactose. In this practical students investigate the treatment of milk with lactase. Following treatment they test the glucose content of the converted milk, and compare products...

As the number of cells in a microbial culture increases, turbidity increases. In this experiment students calculate doubling time and growth rate constant using absorbance as the measure of growth. Turbidity is caused by suspended cells in the growth medium scattering light, and may be measured using a colorimeter...

This experiment is a continuation of Determining Doubling Time. Students create a standard curve of absorbance against yeast concentration, and use this to determine the concentration of yeast produced over time.

The standard curve (dry mass, grams per litre) is generated from known concentrations of dried...

Fruit juice companies use a variety of different treatments and enzymes to maximise their yield. In this experiment students will investigate the effectiveness of these different enzymes.

The enzymes used are designed...

In this experiment students grow yeast on agar plates and look at the effect on growth of some common anti-fungal treatments, which are available to treat conditions such athlete's foot and thrush. Antifungal products may be bought from a local pharmacist, for example, Canistan, Daktarin, Diflucan. Several...

Gelli Baff, a crystalline powder, has been dumped into a bathtub filled with water. How can you force the hydrogel to go down the plughole in order to drain the bathtub? 

In this investigation, students learn about swelling reactions, balanced reactions, and polymerisation. Students should be able to...

Plant gums are often used in the food industry as thickening and stabilising agents. Gums are water soluble polysaccharides, such as starch and cellulose. In this activity, students investigate what happens to the texture when different polysaccharides are mixed.

When solutions of some polysaccharides are...

A Catalyst article about hydrogels. Soft contact lenses, disposable nappies, hair gel and plant water crystals all make use of substances called hydrogels. These are polymers which have the unusual property of being able to absorb huge quantities of water. The article looks at the structure of hydrogels and their...

These resources were developed by the Gatsby Science Enhancement Programme and the Centre for Science Education at Sheffield Hallam University in order to demonstrate new ways that ICT can be used to enhance practical work in science. Research scientists use computer technology in both the collection and the...

This mystery can be used to introduce osmosis and diffusion. 

Two beakers are displayed at the front of the room. Both look identical in that they both contain a plastic zip--lock bag with a starch solution inside. The zip-lock bags are both sitting in a clear solution. What the students don’t know is that...