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Alright, so in this video we're going to continue our discussion on aqueous solutions by talking about electrolytes. So an electrolyte is a substance that contains free ions, and any substance that contains free ion conducts electricity. So basically the free ions act as these charge carriers that can carry an electrical current. And when we talk about electrolytes, generally we have strong electrolytes, weak electrolytes, and non electrolytes. So a strong electrolyte conducts electricity strongly. A weak electrolyte weakly conducts electricity, and a non electrolyte doesn't conduct electricity at all. So basically what it boils down to is, if I have a compound and I dissolve it in water to make an aqueous solution of that compound, will I get a strong, a weak, or a non electrolyte? So we're going to go through a couple scenarios with a couple of different kinds compounds. So suppose we have the following equation. So let's say we have glucose C6H1206 and we dissolve this glucose in water, this is originally a solid, we dissolve this glucose in water and the products that we'll get are just going to be glucose C6H1206. And this is going to be a aqueous now. So upon dissolving the glucose in water, all we've done is just surround each glucose molecule with water molecules. Before they were solid they were packed tightly together, but upon dissolving them in water, they are now aqueous. So now each glucose molecule, like I said, is surrounded by water molecules. So notice that our products side of the equation, the right hand side of the equation, doesn't have any ions in it. So remember an electrolyte has ions, so this is a non electrolyte; So this doesn't conduct any electricity at all. And the process a molecular compounds such as glucose dissolving in water, to become just that molecular compound aqueous, we call that molecular dissolution. So whatever stuff you had just becomes that same stuff but aqueous. That's what molecular dissolution is. So most molecular compounds undergo molecular dissolution when you put them in water, but there are some that don't and we'll go over that in just a little bit. So now suppose I have an ionic compound, such as sodium chloride. So sodium chloride, that would be NaCl, and this is a solid. If I dissolve that in water that's going to give me a Na+ sodium ion, and that's aqueous, and it's also going to give me a chloride ion, Cl-, which is also aqueous. So now our product side of the equation actually has ions in it, and since sodium chloride is a soluble ionic compound it completely reacts to form its products. So when you put sodium chloride in water it completely ionizes into sodium ion and chloride ion. And that's basically what this single reaction arrow means. A single reaction arrow means that whatever our products were these are gone. And whatever our - excuse me - whatever our reactants were, those are gone. And whatever our products are, this is what we have. So a single reaction arrow means we have a complete conversion from reactants to products. Technically there might still some be these minute amount of NaCl that have not yet dissolved, but, it's a good approximation to say that there's a hundred percent conversion between - from - reactants to products. So since we have this one hundred percent conversion from reactants to products, and our products are ions then we can call this a strong electrolyte. And the process of a soluble ionic compound, such as sodium chloride, dissolving into its constituent ions, this is what we call ionic dissolution. So remember back when we were looking at molecular dissolution, molecular dissolution results in a non electrolyte. But ionic dissolution actually results in a strong electrolyte. So now let's go over another scenario. Suppose I have an acid, such as HCl, and I want to put that in water. Well when I put HCl in water, the water actually acts as a reactant. So, we can put water on the left hand side of the equation. And HCl is a gas, H2O is a liquid If I react HCl with water what's going to happen is the HCl is actually going to donate an H+ ion to the water molecule. So an H+ ion actually gets transferred from the HCl to the water. And the products that result from this reaction are Cl- chloride ion, which is aqueous, and hydronium ion, which is H3O+ and that's also aqueous. So again, all we've done was just transfer a H+ ion from the HCL to the water resulting in CO- and H30+. Now since HCl is a strong acid, (so remember that HCl is a strong acid, there are many other strong acids other than HCl, HCl is just one of them) anytime a strong acid reacts with water, you get this complete conversion to Cl- and H3O+. And that's, once again, why I have included the single reaction arrow. Again, technically, there could be some reactant still hanging around but a good approximation is that there's a hundred percent conversion from reactants to products. So if I have a strong acid, or a strong base, and I react it with water that means I'm going to get a complete conversion to these ions, which means that I'm going to to get a strong electrolyte. So let's go over another scenario in which we have an acid reacting with water; but the acid is not a strong acid, it's a weak acid. So, suppose I have a weak acid such as acedic acid, which is CH3COOH, and I dissolve this in water. CH3COOH, that's a liquid. Water is also a liquid. And my products are going to be CH3COO- plus H3O+, and these are both aqueous. Now CH3COO, CH3OOH, that's acedic acid; this is actually a weak acid. So that means that there is not a 100% conversion from reactants to products, there's reactants becoming products but there's also products becoming reactants. And the way that we express this is by using 2 half arrows So remember, when we did the strong acid (HCl) we used a single arrow. But when we do a weak acid, we actually have to use these half arrows because, like I said, you have reactants becoming products, but you also have products becoming reactants. So if this is the case, if you have a weak acid (or weak base) reacting with water, it forms ions, but it doesn't form ions nearly to the extent that the strong acid did. strong acid did. so if a weak acid is dissolved in water than this would result in a weak electrolyte, So if you're trying to do a problem where you have an acid or base and you want to know if it's going to produce a strong or weak electrolyte, you need to know if it's a strong or weak acid. And from there you can determine if it's a strong or weak electrolyte. So, this process where we have, notice the HCl and CH3CooH, those are both molecular compounds. We don't have any metals in there so you have a molecular compound that actually forms ions when you put it into water. And this is what we call molecular ionization. (muttering: let me get a better pen) So molecular ionization, that's when you have a molecular compound that forms ions when you put it in water, that can result in either a strong electrolyte (in the case of a strong acid or base), or a weak electrolyte (in the case of a weak acid or base). So there you go. That is just a general discussion aqueous solutions and electrolytes.

Video Details

Duration: 10 minutes and 37 seconds
Country: United States
Language: English
License: Dotsub - Standard License
Views: 49
Posted by: christineward on Sep 12, 2015


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