Gas evolution was observed when a solution of Na2 S was...

Gas evolution was observed when a solution of $\mathrm{Na}_{2} \mathrm{S}$ was treated with acid. The gas was bubbled into a solution containing $\mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2},$ and a black precipitate formed. Write net ionic equations for the two reactions.

Key Concepts

Spectator Ions

Spectator ions are those ions present in a reactant solution that do not participate in the actual chemical change. In the formulation of net ionic equations, these ions are omitted to simplify the equation and focus solely on the species that are chemically transformed during the reaction.

Precipitation Reactions

Precipitation reactions involve the formation of an insoluble compound from the reaction of two soluble species in solution. This process is driven by the low solubility of the resulting product, leading to its separation from the solution as a precipitate. Such reactions are useful in confirming the presence of specific ions.

Net Ionic Equations

Net ionic equations are simplified representations of chemical reactions that show only the species that undergo a change. They are derived by eliminating the spectator ions—those ions that do not change during the reaction—from the full chemical equations, thereby highlighting the actual chemical processes occurring.

Acid-Base Reaction Leading to Gas Evolution

When a solution containing a basic anion such as sulfide ions is treated with an acid, the anions react with hydrogen ions to form a gas. This process exemplifies acid-base reactions where the proton transfer results in the formation of a gaseous product, demonstrating how acid addition can lead to gas evolution.

Transcript

00:01 We've written a number of reactions, chemical reactions, balanced them, and we've written net ionic reactions.

00:08 This problem asks us to write net ionic equations, but we're not really given every single thing that we need.

00:16 So let's get started.

00:19 We are told that a gas is evolved, so that means i'm going to have gas for a product, when a solution of na2s is bubbled through an acid.

00:35 And i get a gas.

00:39 So i know that information.

00:41 Now there's another step, but we'll worry about that later.

00:44 Okay, so we know that an acid has a hydrogen in it.

00:49 And for us, when we represent acids, we represent acids as h3o plus aq.

01:03 And we also know that our, this would have been an aqueous substance, there's a little aq right there.

01:16 So that would have been a sodium ion and a sulfide ion, two of these, one of these.

01:34 And on this side, my gas would have been h2s, because that is a gas that we all know about.

01:42 And since i'm going to have, i can see that i'd need two of these, i will also have to add two waters.

01:52 Let me go through again how i knew these things.

01:56 Okay, my acid, we represent our acids as h3o plus.

02:03 Since i have two sodiums, i'm going to need two waters.

02:12 Two sodiums, two waters.

02:14 For instance, let's just say for the sake of argument, i had, we'll make this up and say i had hcl.

02:22 If i had n -a -2s plus h -cl yields, h2s plus nacl.

02:38 You can see what's going on here.

02:40 I need a two here and i'd need a two here.

02:44 This would be aqueous.

02:48 So my sodium and my chlorines are all going to be spectators.

02:54 Okay...

Please give Ace some feedback