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Water as a solvent

Water, due to its polarity, acts as a fantastic solvent, especially for polar substances and ions. This is because the positive and negative ends of water molecules are attracted to ions, allowing them to dissolve. This property is crucial for chemical interactions within cells. However, non-polar substances like hydrocarbons do not dissolve well in water and are termed hydrophobic. Created by Sal Khan.

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  • mr pants teal style avatar for user Eleanor
    Why does salty water still taste like salt if the individual Na and Cl atoms are no longer 'working together' as part of a structure? One of the previous articles said that NaCl isn't a molecule, just a module that is repeated to form a crystal - is it the same with all crystals made of single atoms, that the component atoms in the right proportions will taste the same as the crystal?
    (51 votes)
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  • leaf green style avatar for user SeanODBrown
    I thought sodium was explosive in water. Why doesn't it explode if it separates from Chlorine?
    (28 votes)
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    • male robot hal style avatar for user Malay Kedia
      The sodium has already given its electron to the chlorine. So, they form Na+ and Cl- ions. Since they have opposite charges, they develop a bond known as ionic bond.
      Now, when NaCl is added to Water, the the hydrogen bond between water molecules becomes more powerful than the ionic bond between Na+ and Cl- ions, due to the more amount of water in the solution.
      This causes NaCl to separate into Na+ and Cl- ions. But still, the chlorine has not returned the electron to sodium, due to which both of them remain stable. But since they have developed charges on them, the partially positive side of H2O or H atoms get attracted to Cl(which is negatively charged) while the partially negative side of H2O or O atom gets attracted to Na(which is positively charged).
      This causes it to dissolve in water.
      But now, the sodium is already stable, and does not need to react to water to become stable. So no reaction occurs between water and Na+ ion, and no explosion occurs.
      (42 votes)
  • male robot johnny style avatar for user higgsphoton1
    At Sal makes it seem that the sodium chloride had separated, is this what happens in real life (I doubt this), or is it that they are separated for clarity and are actually still joined in their ionic bond.
    (14 votes)
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    • piceratops seed style avatar for user RogerP
      Once dissolved, the sodium ions and the chloride ions separate, and each is surrounded by water molecules. This is known as solvation and this stabilises the ions. The ionic bonds between the sodium and chloride ions are no longer there.
      (19 votes)
  • blobby green style avatar for user Auna Fujitani
    How does Oxygen dissolve in water? O2 is non-polar so it cant bond with H20.
    (10 votes)
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  • piceratops tree style avatar for user Auver
    Why does sodium have a positive charge?
    (4 votes)
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    • starky ultimate style avatar for user briantlegvold
      First off, electrons are negatively charged while protons are positively charged, and elements in general are found in a neutral state with equal numbers of protons and electrons. This means that if an element looses an electron, that element will then have more protons than electrons, and thus be positively charged.
      Now for why sodium is generally positively charged, the easiest way to think about it is that on the far right side of the periodic table you have the noble gases, (Group 8A) helium, neon, argon, etc. These noble gases are inherently very stable and have very little to no reactions with other elements (generally speaking). The point is that all other elements want to be like the noble gases, that is to say that other elements want to have a similarly stable electron configuration. So the halogens (Group 7A) want to gain an extra electron to be more like the noble gas in there same row. On the other end of the spectrum over by sodium in the alkali metals (Group 1A), they have just one more electron than the noble gas in the row above it (i.e. sodium has only one more electron than neon does). This means that it is easier for sodium to loose just one electron to be like neon, rather than gain an extra seven electrons to be like argon.

      I hope this helps.
      (22 votes)
  • leaf grey style avatar for user brok3nwir3
    I feel like there is something missing from this video... I can understand the molecular interactions that Sal is describing, but why does this lead to the salt dissolving; why doesn't the salt keep it's form in water?
    (9 votes)
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  • aqualine ultimate style avatar for user Alexandra Holloway
    In middle school science class I remember learning about physical and chemical reactions. Physical reactions are things like mixing a tablespoon of salt in water, creating "salt water", whereas mixing baking soda and vinegar to make a volcano is a chemical reaction. In both physical and chemical reactions, what is the difference? Sal is drawing salt water like the molecules are joined together. Does this happen in both kinds of reactions? Sorry if my question is a little bit confusing.
    (7 votes)
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  • orange juice squid orange style avatar for user woolsilvi
    Why does salt water taste salty if the ions of the salt molecule have been separated?
    (5 votes)
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  • blobby green style avatar for user annalia.sellers
    What do the little 8's with charges represent. I understand what the charges represent, just not the 8's. I don't even know if they are 8's.
    (2 votes)
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  • orange juice squid orange style avatar for user Tameka Moore
    if salt can dissolve in water can sugar?
    (4 votes)
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Video transcript

- [Voiceover] We've already talked about the notion that a water molecule has polarity to it. One end has a partially negative charge, and the other end has partially positive charges. And we've talked about how this leads to hydrogen bonds, and we alluded to the fact that maybe these hydrogen bonds give us all sorts of neat properties of water. And what I want to talk about in this video is one of those very important properties, and that's water's ability to be a solvent Water's ability to be a solvent. And this means that it's easy for certain things to be dissolved inside of water. And that's super important, because that's how a lot of the chemistry occurs, by things getting dissolved in water and then interacting and bumping with other things. And this is actually what's happening inside of cells, in the cytoplasm. The cytoplasm, which is mostly water, is a solvent which allows a bunch of interactions to happen between different types of molecules. But let's think about why water is a good solvent, and what types of things it can dissolve easily and what types of things it might not be able to dissolve so easily. So the key feature that makes water a good solvent, or at least a good solvent for a large class of molecules, is its polarity. If I were to take some sodium chloride, often known as table salt, so let me... So if I were to take sodium NaCl, sodium chloride. Sodium chloride, the sodium and chloride are attracted by ionic bonds. The sodium right over here has a positive charge, it has an electron stripped from it, and the chloride has a-- let me write that in a different color. So the sodium has a positive charge, because it has an electron stripped from it, and the chloride, it is an anion, it has a negative, it is a negatively charged ion, because it gains an extra electron. But they are attracted to each other. This has a positive charge, this has a negative charge. This is called an ionic bond. But if you put sodium chloride in water, something very interesting happens. This is something that we've all experienced. Take some table salt and put it in water and see what happens. It will dissolve. And why does it dissolve? Well, let's draw it out. So this is the sodium right over here. So that's the sodium. It has a positive charge. It has a positive charge. And then this is the chloride right over here. It has a negative charge. What's gonna happen if you put it inside of the water? Let me do that negative charge in the green. What's gonna happen when you put it inside of water. Well, you can imagine. The negative ends of the water molecules are going to be attracted to the sodium ion. So it's going to look something like this. So you have the oxygen, oxygen, oxygen, oxygen, oxygen, I'm clearly not drawing things to scale, but this'll just give you the idea. This end of the water molecule all has a partially negative charge. Partially negative charge. So it's going to be attracted to the positive sodium ion. And then the hydrogen ends, the hydrogen ends, are going to have a partial positive charge, and then they're going to be repelled. They are going to be repelled from the positive sodium ion. So it's gonna look something like this. And it's gonna look something like this. And you're gonna have partial positive charge on the outside. Partial positive charge on the outside. And now these hydrogens over here, this will just interact with water the way that it would typically, with the hydrogen bonding, the molecules just flowing past each other. So the fact that the sodium ion here, it's an ion, it has charge. It is able to dissolve in the water very easily, because it is attracted to the partially negative ends of the water molecule. Now, a similar thing is going to happen with the chloride ion. And we call a negative ion an anion. So over here, over here, and actually let me get some, let me move it over a little bit so that I have some space. So the chloride anion, let me move it over a little bit. So right, or maybe I'll move it over here. So the chloride, the chloride anion, let me see, I'm having trouble with my selection tool. Alright. So there we go. The chloride anion has a negative charge that's going to be attracted to the positive end of the water molecules. So you could imagine something like this. So the hydrogen ends, the hydrogen ends, are going to be attracted to it, they have a partially positive charge. They have a partially positive charge. And of course you have the oxygen end that has a partially negative charge. It has a partially negative charge. And I could draw more of these. Hydrogen, hydrogen, attracted there, you have the oxygen over, let me do that, I wanna keep my colors consistent. The oxygen right over there, we have the hydrogen, once again this isn't drawn to scale. Hydrogen, it is bonded to the oxygen. And so once again, you can form this, so you could almost imagine this shell of water molecules is going to be attracted to it, it's going to be attracted, or I guess you could say the partially positive end, which is where the hydrogen atoms are, is what's going to be attracted to this negative ion. So this is partial positive over here. And then on the partially negative side, outside of this shell, you can imagine it's just gonna interact with the water just the way any water molecule would, and so it's gonna be able to flow very easily. So you probably see something interesting here. If something has charge, if it's an ion, or if something has some polarity, it's very easy to dissolve it inside of water. And in this case, and just to have some terminology here, in this case, water is the, water is the solvent, so water is the solvent. So the solvent is water. And the thing that's being dissolved in the water, we call that a solute. So we call this the solute. So the sodium chloride. That is, you could use sodium chloride as a solute, or you could say that the sodium ions are a solute and so are the chloride ions. That is also considered to be the solute. And so you say, well what kind of things dissolve well? Well, things that that have charge or that are polar. And things that are charged and polar and tend to dissolve well in water, there's another word we use for them. We say that they are hydrophilic. So we could say that this right over here is hydrophilic. And if you look at the word root, hydro is referring to water. So hydro is referring to water. And philic means loving. So this literally means water loving. Water loving. Hydrophilic. And so you might be asking, okay, everything we've talked about, you know, we've seen water molecules, that's polar, we're looking at charged ions, okay we could get that, we can get why they'd be hydrophilic, they can incorporate themselves well into the water, but what are examples of things that would not incorporate themselves well in water? Well, in general, things that don't have charge, or that aren't polar, aren't going to be able to dissolve in water all that well. And a good example is hydrocarbons. So if you took some hexane. And hexane is a major constituent of car gasoline. So hexane, hex the prefix means six carbons. So let's see, one, let me do this in another color. So we have one, two, three, four, five, six carbons. So one two three four five six carbons. And then all the other bonds are with hydrogens. So let me draw this as well as I can. Carbon, at least typically, forms four bonds. So hydrogen, hydrogen, hydrogen, hydrogen, hydrogen, hydrogen, hydrogen. This right over here is hexane. This thing has no polarity to it. It doesn't form hydrogen bonds, it doesn't have any polarity. And so if you were to take hexane and throw it into water, it's not going to dissolve that well. It's actually going to kind bead up. And you would see that if you actually threw some gasoline inside of water. So things like hexane we would call hydrophobic. Hydrophobic. So this right over here is hydrophobic. Hydrophobic. It'll literally ball up to avoid getting in touch, to minimize its contact with water. Because the water is attracted to itself, and it is not so attracted to this stuff right over here. And hydrophobic? You still have hydro, meaning water, and then phobic, it means fearing. So this right over here is water fearing. That's why it's hard to mix things like water and oil or gasoline and water.