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I am stuck on a homework question that states:
A piece of solid bismuth is heated strongly in oxygen.
The answer key states the answer as $\ce{Bi + O2 → Bi2O3}$. However, it is to my understanding that the metal Bismuth has a charge of +5 because of its location on the periodic table. Therefore, $\ce{(+5)[charge of Bi]*2 + (-2)[charge of oxygen]*5 = 0}$ giving me $\ce{Bi2O5}$. Please advise.
Many elements have multiple valencies. The most common oxidation state of Bi is +3. Bismuth (V) is also possible. Read more here on Bismuth oxides.
It is true that bismuth burns with a bluish flame in the presence of air to form bismuth trioxide($\ce{Bi2O3}$) as @M.Farooq mentioned. Bismuth pentoxide is not a pure compound but a mixture of various compounds like water, bismuth trioxide and bismuth tetroxide. It is also not stable at strong heat, decomposing at 393 K. Also, there is no direct preparation for this compound. You have to first make bismuth trioxide and then react with a bunch of other chemicals to form bismuth pentoxide.
So, the balanced reaction would be:
$$\ce{4Bi + 3O2 ->[\Delta] 2Bi2O3}$$
