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Arsenic pentoxide facts for kids

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A 3D-model of arsenic pentoxide.

Arsenic pentoxide, also known as arsenic(V) oxide, is a chemical compound. Its chemical formula is As2O5. It has arsenic and oxide ions in it. The arsenic is in its +5 oxidation state. More common is arsen in its oxidation state +3 as As2O3 (arsenic trioxide or arsenic(III) oxide). The LD50 for arsenic pentoxide is 8mg/kg for rats. When the substance becomes wet, it turns into arsenic acid, which corrodes metals.


Arsenic pentoxide is a white, odourless solid. It dissolves easily in water to make arsenic acid. It is highly toxic, as are almost all arsenic compounds. It is a powerful oxidizing agent. It reacts with hydrochloric acid to make chlorine. As2O5 breaks down to arsenic trioxide and oxygen when heated to about 300°C.

As_2O_5 + 268.1 kJ \rightarrow As_2O_3 + O_2

It reacts with bases to make arsenates. The energy for the reaction is taken from the heating.


Arsenic pentoxide cannot be produced by burning arsen. That only results in As2O3. To produce arsenic pentoxid, arsenic acid will be dehydrated. This is done with phosphorus(V) oxide.

2 H_3AsO_4 \rightleftharpoons As_2O_5 + 3 H_2O

The arsenic pentoxide drops out as white powder.


Arsenic pentoxide is used to make pesticides and insecticides. It is also used in glass industry.

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