What are the spectator ions in this equation?

Question

Sodium thiosulfate + hydrochloric acid -> Sodium chloride + water + sulfur dioxide + sulfur

Na2S2O3 (aq) + 2 HCl (aq) -> 2 NaCl (aq) + H20 (l) + S02 (g) + S (s)

Break apart

2Na + 2S + 3O + 2H + 2Cl -> 2Na + 2Cl + 2H + 0 + S + 2O + S

so Na, Cl, and H are spectator ions, correct because same number on both sides.

But what about O and S?

Can I consider 2S on 1 side to cross off S+S on the other side?

That means all of these are spectator ions = Na, Cl, H, O, S ??

Thank you

Answer 1

Na₂S₂O₃ (aq) + 2 HCl (aq) ==> 2 NaCl (aq) + H₂0 (l) + S0₂ (g) + S (s)

Break apart (only those can can be "broken apart") to give the total ionic equation:*

2Na⁺(aq) + S₂O₃^2-(aq) + 2H⁺(aq) + 2Cl^-(aq) => 2Na⁺(aq) + 2Cl^-(aq) + H₂O(l) + SO₂(g) + S(s)

Spectator ions are the ones that appear on BOTH sides of the equation. In this case they would be....

Na⁺

Cl^-

*Hint: when "breaking apart" things, don't break apart the cations and anions of polyatomic ions separately. For example, for NH₄Cl, break it up as NH₄⁺ and Cl^-, but don't break up the cation, NH₄⁺. For Na₂SO₄, break it up as 2Na⁺ + SO₄^2-, but don't break up the anion, SO₄^2-. Also, never break up H2O(l) or any gases or solids. They remain as is.

Answer 2

Hey Mary -

What's missing from your thought process here is the charge ("oxidation state") of each element. For example, in sodium thiosulfate, the sodium has a +1 charge, which is balanced by a negative 2 charge on the thiosulfate group to create that neutral molecule. This is a tricky molecule, because it takes 2 steps to break it down successfully and determine all oxidation states. Also, thiosulfate has some unintuitive mix of oxidation states, so I'd recommend drawing a Lewis structure to figure out what's going on - and probably checking your work after.

Once you've assigned a charge to every ion, you can determine which are "spectators" - they are the ones that don't change charge at all. Having the same number on both sides does not help you determine spectator ions - that is a mandatory feature of any balanced equation.

Some other notes:

1) You asked about combining sulfur ions - this only works if the charges are identical. In your case, the sulfurs on the right side should not have the same charge.

2) It is helpful to know that elemental solids (like S(s)) have a charge of 0. Therefore, sulfur cannot be a spectator ion, as it must have changed charge at some point and, on the right side, it's not even an ion at all.

Hope this helps,

Chris