Theory

The reaction is usually written as:



but this is an oversimplification. Some of the carbon is oxidised to carbon dioxide and carbon monoxide and some of the sulphuric acid is reduced to sulphur dioxide. There are probably other products.


Further Details

This demonstration is a spectacular warning of the danger of handling concentrated sulphuric acid. Eye tissue is almost entirely water.

Extension

Glucose can be dehydrated in the same way, but it is a little slower and there is a longer lag time before the reaction gets underway.


Safety

Wear eye protection.

Work in a fume cupboard because of the gases evolved.

The carbon 'sponge' can be a disposal problem. Place it in its beaker in a large bowl of water and leave for some time to dilute any remaining acid. Small quantities can be boken up with a gloved hand and flushed down the sink. Larger amounts can be placed inside several sealed plastic bags and placed in the dustbin.