Label each of the following substances as an acid, base, salt, or none of the above. Indicate whether the substance exists in aqueous solution entirely in molecular form, entirely as ions, or as a mixture of molecules and ions. (b) acetonitrile, CH3CN

Question

Accepted Answer

welcome back everyone in this example, we need to identify if ethyl amine CH three CH two and H two as an asset base or salt. So this is for part one of our prompt and then in Part two we need to indicate and we'll use a different color. We need to indicate whether ethyl amine exists in solution as associated molecules or as a mixture of unassociated molecules and ions or as just ions only. So our first step is to write out our reaction. So we have our molecule ethyl amine. So that's CH three CH two, NH two and we're going to draw it out in the expanded skeletal structure. So we would have our methyl group here where we have our first carbon atom which is our CH two group. Or recall that that is together CH three CH two considered an ethyl group. And then we have bonded to this CH two a NH two, so a nitrogen atom bonded to two hydrogen atoms and we'll just condense that and place our two electrons on nitrogen. Because we should recall nitrogen has a bonding preference of having three bonds and one lone pair. Now with the presence of those lone pair electrons on the nitrogen atom that creates negative character here for our ethyl amine molecule and we are going to be dissolving this in a solution. So we're going to be reacting with water. So we'll draw the molecule H and then we have O. H. So this is our water molecule and as we stated because we have this negative character coming from our lone pair of electrons on our nitrogen atom and ethel mean we can understand that ethel min is going to be considered therefore a nuclear file. We also want to recall that as a whole. Our NH two group on our ethylene molecule is considered an aiming group. And we want to recall that a means, sorry, that's a M I N E S R week basis. And so recall that being a weak base means that this ethyl amine molecule is only going to partially dissociate in solution. So it's going to partially dissociate. And because we know it's a weak base and a nuclear file, we can specifically also recognize that it's a louis space which we would understand, meaning that our ethyl amine molecule is an electron donor. So recall that our protons or our hydrogen atoms on our water molecule have a positive charge, so positive character. And we would have a nuclear filic attack coming from our electrons on our ethylene molecule and targeting one of our protons on our water molecule. Now, as it targets the positive character on our proton, it's going to form a bond with one of the protons in our water molecule. And so this arrow represents that bond forming between the two molecules. But as we recall, hydrogen should only be able to form one bond. And so that means that as that bond with ethyl amine forms our bond on our water molecule between our proton and our oxygen atom is going to collapse as electrons onto our oxygen atom. And so these two arrows happen at the same moment where we would form our products. And as we stated, this is a weak base. Our element is a weak base, so it's only going to partially dissociate. And for our reaction arrow we should have a double arrow where our arrow going towards our products is going to be a smaller distance than our arrow going back towards our reactant here because we only go through a partial dissociation of our ethyl amine, meaning it's not going to fully dissociate into our products here now for our first product because we form that bond with the proton, we have CH three, CH two, and then now we have NH three where our nitrogen atom will now have a positive charge because it has a total of three bonds instead of Or sorry, it has a total of four bonds instead of the three that I would prefer to have, and it no longer has a lone pair. And this product we should recognize as methyl amine, whereas our second product we should recognize is going to be hydroxide where we now have a minus one formal charge on our oxygen atom because it now has those extra electrons from the bond that it once shared with its second proton or second hydrogen atom here. And so are oxygen atom now has a total of three lone pairs creating our hydroxide product here. And we would recognize this as an ion, whereas methyl amine is also an ion because it has that plus one caddy on charge. And so based on this reaction that we've outlined, we can say that therefore our ethyl amine for part one of our question is a base and we can say it's specifically a weak base because it's not on our list of memorized strong basis and we would say, and it exists in solution because we know it's a weak base, it's not going to fully dissociate. So it exists in solution as an unassociated molecule and a mixture of ions which would be our products that we've outlined on the right hand side of our equation. And so for our final answer, we have our statement here below defining what we mean is and how it exists in a solution. So I hope that everything I went through was clear. If you have any questions, please leave them down below and I will see everyone in the next practice video

Label each of the following substances as an acid, base, salt, or none of the above. Indicate whether the substance exists in aqueous solution entirely in molecular form, entirely as ions, or as a mixture of molecules and ions. (b) acetonitrile, CH3CN

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Key Concepts

Acids and Bases

Ionic and Molecular Compounds

Solubility and Aqueous Solutions