Aluminum metal reacts with aqueous cobalt (II) nitrate to form aqueous aluminum nitrate and cobalt metal. What is the stoichiometric coefficient for cobalt when the chemical equation is balanced using the lowest whole-number stoichiometric coefficients?

the stoichiometric coefficient for cobalt is 3

Explanation:

the unbalanced reaction would be

Co (NO₃) ₂ + Al → Al (NO₃) ₃ + Co

One way to solve is to build a system of linear equations for each element (or group as NO₃), knowing that the number of atoms of each element is conserved.

For smaller reactions a quick way to solve it can be:

- First the Co as product and as reactant needs to have the same stoichiometric coefficient

- Then the Al as product and as reactant needs to have the same stoichiometric coefficient

- After that we look at the nitrates. There are 2 as reactants and 3 as products. Since the common multiple is 6 then multiply the reactant by 3 and the product by 2.

Finally the balanced equation will be

3 Co (NO₃) ₂ + 2 Al → 2 Al (NO₃) ₃ + 3 Co

then the stoichiometric coefficient for cobalt is 3