Write a balanced net ionic equation for the redox reaction of Ag2S and Al metal that produces Ag metal and Al(OH)3.

Question

Write a balanced net ionic equation for the redox reaction of Ag₂S and Al metal that produces Ag metal and Al(OH)₃. 

Low concentrations of hydrogen sulfide in air react with silver to form Ag₂S, more familiar to us as tarnish. Silver polish contains aluminum metal powder in an alkaline suspension.

Answer 1

To write a net ionic equation you first have to figure out which ions are working in an aqueous state. Since the Al (normally a solid) is in a solution it is aqueous in this case. Since the Ag2S is also aqueous we can then just write the equation: Ag2S + Al + H2O = Al(OH)3 + Ag + H2S.

Now the Al(OH)3 and Ag on the product side are solids and are therefore precipitates and are included in the redox reaction. The Hydrogen and Sulfur are spectator ions and therefore are not included in the redox reaction. Another helpful way to identify which ions should be included in a redox equation is to see which ions change charge in a reaction and those are the ones being reduced or oxidized.

Ag on the reactant side has a charge of +1 and on the product side has a charge of 0 so it is being changed.

We write that as: Ag+1 + e- = Ag. (an electron is added to the ion to create an element with no charge)

Al on the reactant side has a charge of 0 and on the product it has a charge of +3.

We write that as: Al= Al+3 + 3e- (three electrons were removed from the Al to make an ion).

If we remember the mneumonic LEO the lion goes GER this helps us remember that Losing Electrons Oxidized, Gaining Electrons Reduced.

So, since the Ag gained an electron it was reduced and the Al lost electrons so it was oxidized.

Now that we have those half reactions we can just write them together that gives us the net ionic reaction.