Hydrogen sulfide gas is bubbled into an acidified solution...

Hydrogen sulfide gas is bubbled into an acidified solution of potassium permanganate; elemental sulfur precipitates. The unbalanced equation is $\mathrm{H}_{2} \mathrm{~S}(\mathrm{~g})+\mathrm{MnO}_{4}^{-}(\mathrm{aq})+\mathrm{H}^{+}(\mathrm{aq}) \longrightarrow \mathrm{Mn}^{2+}(\mathrm{aq})+\mathrm{S}(\mathrm{s})+\mathrm{H}_{2} \mathrm{O}(\ell)$ (a) Potassium ions are not given in the equation. Explain why. (b) Explain why this is a redox equation. (c) Identify the oxidizing and reducing agents.

Hydrogen sulfide gas is bubbled into an acidified solution of potassium permanganate; elemental sulfur precipitates. The unbalanced equation is
$\mathrm{H}_{2} \mathrm{~S}(\mathrm{~g})+\mathrm{MnO}_{4}^{-}(\mathrm{aq})+\mathrm{H}^{+}(\mathrm{aq}) \longrightarrow \mathrm{Mn}^{2+}(\mathrm{aq})+\mathrm{S}(\mathrm{s})+\mathrm{H}_{2} \mathrm{O}(\ell)$
(a) Potassium ions are not given in the equation. Explain why.
(b) Explain why this is a redox equation.
(c) Identify the oxidizing and reducing agents.

Key Concepts

Spectator Ions

These are ions present in a solution that do not participate directly in the chemical reaction. They remain unchanged on both sides of a reaction and are omitted from the net ionic equation to simplify the representation of the chemical change.

Redox Reactions

Redox, or oxidation-reduction, reactions are processes in which electrons are transferred between chemical species. In such reactions, one species is oxidized (loses electrons and increases in oxidation state) while another is reduced (gains electrons and decreases in oxidation state). The balanced electron transfer is a key feature of any redox reaction.

Oxidizing and Reducing Agents

The oxidizing agent is the substance that accepts electrons and is reduced in the process, whereas the reducing agent donates electrons and is oxidized. Identifying these agents is fundamental to understanding the direction of electron flow and the overall mechanism of a redox reaction.

Transcript

00:01 So let's take a look at the reaction between hydrogen sulfide and potassium permanganate in an acidic solution.

00:11 And so you can see here the hydrogen sulfide, the acidic solution is symbolized by the h -plus here.

00:19 But i mentioned the fact that we had potassium permanganate.

00:23 And you can see i only have the permanganate ion sitting here.

00:26 So where's the potassium? well, remember, potassiums are soluble.

00:31 So they are always in their ionic form when they're aqueous.

00:35 So we would have it as something aqueous on the reactant side, something aqueous on the product side.

00:41 And that would make it a spectator ion.

00:43 And remember, in a net ionic equation, spectator ions aren't written.

01:01 So what type of reaction is this then if we see the ions? well, let's take a look.

01:09 Because if you notice we have a permanganate ion here total charge of negative one and we know that from an oxidation number perspective oxygens are negative two so four we have four negative twos negative eight which means that the manganese has to have a plus seven charge just oxidation state, i should say, to start here.

01:42 But over on the product side, it's plus two.

01:47 So that means that the manganese is undergoing reduction.

01:54 Let's see if something is undergoing oxidation.

01:57 Well, over here with the hydrogen sulfide, it's a neutral substance.

02:02 So the sum is zero.

02:04 We have two hydrogens each at plus one, which must mean that the sulfur has an oxygen.

02:11 State of minus 2.

02:13 But over here on the product side, it's an element in its natural state.

02:17 So it's zero...