Why Does Sugar Burn When You Put Ashes on It?

Written by kristin jennifer
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Why Does Sugar Burn When You Put Ashes on It?
Sugar does not catch fire without help from a catalyst. (Comstock/Comstock/Getty Images)

Sugar is the granulated product of processed sugar cane. It will not burn or catch fire if directly in contact with a flame. Sugar will melt slowly under constant heat, turning eventually into caramel and, finally, to black carbon in its final stage. However, if ash is placed directly onto sugar and a flame is applied, sugar will catch fire and melt directly into carbon.

Surface Area

Sugar has a large surface area. In a sugar cube, thousands of individual granules are compressed together. As a result, a sugar cube will not respond quickly to heat and will not catch fire. The time it takes for the sugar to respond to the direct flame is simply too long for a fire to ignite.


Adding ash to the sugar enables the sugar to melt faster. Ash is pure carbon. The ash itself will catch fire, but the chemical reaction between the ash and the sugar will cause the sugar to react faster to the heat from the flame. The sugar will then melt into liquid black carbon. The ash does not change at all; it has acted as a catalyst instead. A catalyst is a substance that increases the speed at which a chemical change occurs.

Types of Catalysts

Catalysts are either heterogenous or homogenous. The ash used to speed up the melting of sugar is a heterogeneous catalyst. Although the ash and the sugar are both solids, they are physically separate even when placed together. As such, the ash represents one phase and the sugar another. The ability to differentiate the two phases makes ash a heterogenous catalyst. Homogenous catalysts are those catalysts which form a single phase or solution when placed together with a substance.

Other Uses for Catalysts

The use of catalysts is necessary in a variety of industries. Catalysts are necessary to convert crude oil into gasoline and in reducing emissions in motor vehicles. Synthetic polymers are created with catalysts for use in paint, textiles, packing materials, biomedical and electronic devices. A catalytic reaction is necessary for turning wine into vinegar and for leavening bread as well.

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