Science - Eye of newt, toe of frog

26th October 2012 at 01:00

What it's all about

"I've searched the stockroom and there's no trace of it," I tell the science coordinator.

"No trace of what?" she asks.

"Sweltered venom of a cold toad," I reply. "Neither can I find any eye of newt, toe of frog, wool of bat or tongue of dog."

We are writing our "Double, double, toil and trouble" poems for Halloween - and studying irreversible changes in science, writes Steve Eddison. I want to link them together by making a witch's brew that boils and bubbles to dramatic effect.

Grendel suggests foaming cauldrons. First, the children make cauldrons using black plasticine. Then they form a small cavity in the top, to throw in a few hellish ingredients.

Once their cauldrons and poems are perfected, and in between shrill chants of "Double, double, toil and trouble", First Witch throws in the ground bones of a raven, Second Witch adds extract of squashed frog and Third Witch drops in vile venom of a vicious viper. All three hags cackle as their brew spews its evil contents over the table and fills the air with foul vapours.

During our science of witchcraft debrief, our magical ingredients turn out to be baking soda (sodium bicarbonate), vinegar (acetic acid) and green food dye for dramatic effect. The children are shown how the acetic acid reacts with sodium bicarbonate to produce carbon dioxide, the gas responsible for the fizzing and bubbling. They then learn that this is an irreversible change because the reaction leads to new materials being formed.

What else?

Try erhgiez's 11-lesson scheme of work, workbook and PowerPoint for teaching reversible and irreversible changes. bit.lytesScienceChanges.

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