Explain what bonds must be made or broken and where the electr...

Question

Explain what bonds must be made or broken and where the electrons go when the hydrogen-bonded water between the two amines shown on page 507 reacts to form an amine, ammonium ion, and OH⁻.

Accepted Answer

All right. Hi, everyone. So this question says to refer to the two dimethyl amine molecules hydrogen bonded with water shown below, identify the bonds made or broken and where the electrons go when they react forming an amine, an ammonium ion and hydroxide. So here we have four different answer. Choices proposing whether or not an O and NH bond have been broken or made as well as how many electrons have been transferred if any. So recall first and foremost, right, that dimethyl amine is a neutral amine and therefore a weak base. So the reaction of dimethyl be and water is going to be an acid base reaction specifically in equilibrium because this is a weak base. So water would behave as an acid. So in this case, right, there will be an equilibrium between dimethyl amine and water to produce oops their conjugate acid and conjugate base respectively. Now, the base dimethyl amine gets pronated to produce its conjugate acid, which would be the dimethyl ammonium ion. And so because water is our acid, water would get detonated to yield its conjugate base, which is hydroxide. So, to understand, first of all, the bonds that are being broken and formed because our amen here is a base, right? It is accepting the proton that has been removed from the acid. So therefore, right, a bond between nitrogen and another hydrogen is created during this process. Whereas the acid, specifically water is losing a proton. So a bond between oxygen and hydrogen is therefore broken. So because of this information, I can actually go ahead and eliminate options A and B because both options, A and B propose that it is the NH bond that is broken, which would be incorrect. So to understand how many electrons have been transferred during this process, we have to go ahead and count them for both the acid and the base and their conjugates. So in this case, I'm going to go ahead and copy my reaction here because I'm going to scroll down and proceed with counting how many electrons each species has, right. So here's our reaction. And so first, I'm going to go ahead and count the number of electrons present in the structure of dimethyl amine. No recall that the number of electrons is going to be counted by considering how many valent electrons each atom has. Right. So I would recall the number of valence electrons that carbon nitrogen and hydrogen have and multiply them by their respective amount in the structure of dimethyl amine, right. So carbon, for example, is in group four A and therefore has four valence electrons. So when I multiply this by two because there are two carbons in dimethyl amine, I get a total of eight electrons, nitrogen is in group five A. So it's five electrons multiplied by one nitrogen atom. And that gives me five electrons in total. Whereas hydrogen has only one valence electron modified by seven in the structure of dimethyl amine. And that gives me seven electrons from hydrogen. So when I add everything together, 85 and seven, I get 20 electrons total. So here I'm going to go ahead and proceed with the number of electrons present in the structure of dye methyl ammonium. So the first thing I want to point out here is that dimethyl ammonium has the same atoms as dimethyl amine. So I'm going to go ahead and start off with 20 electrons. However, I do have one extra hydrogen. So I would add one additional electron to give me a total of 21 electrons. But right, because the charge is positive, I would go ahead and actually remove one electron from my total to take into account the charge. So that means that I have 20 electrons still in the structure of dimethyl ammonium. So now I can do the same thing or both water and hydroxide, right. So continuing off with water, I only have two types of atoms. In this case, hydrogen and oxygen. Oops let me actually scroll down a bit there for water. I've got hydrogen and oxygen hydrogen has one valent electron multiplied by two, gives me two in total, an oxygen is in group six A. So that is six valence electrons multiplied by only one oxygen atom in the structure of water. And that gives me a total of six from water. So now when I add everything together, I get that there are a total of eight electrons in the structure of water. So now lets consider hydroxide. Now notice how hydroxide has the same number of electrons as water except for one hydrogen being missing. So therefore, I would take my total of eight electrons in water and subtract one electron from that to account that one hydrogen has been removed. So that would give me a total of seven electrons. However, I do have a negative charge and because I have a negative charge, I'm going to add one electron to my total. So that's one more electron to give me a total of eight still. So notice how throughout the course of this reaction, right, the number of electrons in both the acid and base as well as their conjugates don't actually change. So therefore, we can confirm that no electrons are actually transferred during this process. So with this in mind, if I scroll up one more time to consider our answer choices, the correct answer is going to be option c because 10 bond in water is broken, an NH bond is made and no electrons are transferred. So with all that being said, if you stuck around to the end of this video, thank you so very much for watching and I hope you found this helpful.

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Explain what bonds must be made or broken and where the electrons go when the hydrogen-bonded water between the two amines shown on page 507 reacts to form an amine, ammonium ion, and OH⁻.

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