3 Feb 2007

Do we need to know about dispersions?

Most of the matter and materials that surround us aren't pure compounds or true, homogeneous solutions. If we want to give a science education that is relevant and connected to everyday life, why then is so much of the labwork we do focussed on pure substances and solutions? ...and will the home-/professional cook benefit from knowing a little about dispersions?

A look in the kitchen cupboard and fridge revealed, apart from water and air, the following pure compounds and true homogeneous solutions: sugar, salt, natron (sodium bicarbonate), some of the soft drinks, and some refined vegetable oils. All the other stuff is dispersions, i.e. more or less stable mixtures of compounds/phases that don't mix.

Dispersions and colloids
A related word is colloids, but to my knowledge the word dispersions has lately been adopted as a collective term for colloids, aerosols, foams and emulsions. A dispersion is a homogeneous mixture of two or more phases that are immiscible (won't mix). What is mixed are solids, liquids and gases. The table below gives an overview. In fact, it's quite an enlightening exercise to have a look around and try categorizing the stuff around you. Bread is a foam; cheese, most vegetables and meat are gels; milk, butter and mayonnaise are emusions, just to mention a few.

Click picture for full size version in new window. Click here for Norwegian version

Why dispersions?
In Norwegian school science books and science teacher training literature, matter is divided only into pure compounds and mixtures, see below. The problem with this is that students (and teachers) don't get a language to deal with the stuff that surrounds them. To most of us, foam is a known phenomenon, and emulsions are also known to some. However, these are secondary terms rather than the primary term dispersion.

The term dispersion is not mentioned in the Norwegian curriculum for primary,secondary and high school (Kunnskapsløftet, eng.: "The Knowledge Promotion"). Do I think the term dispersion should have been included in the curriculum? Maybe, maybe not. This new curriculum isn't meant to give detailed instructions to what should be taught, but to what competences the students should have inherited after a certain level. It's up to the school/teacher to fill he subjects with a content as long as the students achieve these competences.

So, if we want the kids to experience a science education related to their everyday life, rather than stuff they'll meet only in science lab, maybe we should start talking about (and playing with) dispersions.

Also, for those of us who would like to benefit from scientific knowledge when we cook, this may afford a good way of viewing ingredients and foods (i.e. previous entries on Tomato foam and Egg white foam).


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Addition to this post in the following post "Do we need to know about dispersions: addition"

1 comment:

  1. Hilary Burrage17 May, 2008

    You're right of course that food is absolutely central, and can be used for all sorts of teaching.

    I've recently written a piece on my own blog called Food: What do we need to know?

    By the time it was finished (for now) I'd asked hundreds of questions but found very few answers! There's an awful lot of scope in food for school projects (and experiments) as well as top-level research...

    Best wishes,


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