How Does Hot Water Dissolve Salt?

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When hot water is combined with salt, the main interaction is the breaking of different bonds that then results in weak bonds or interactions forming between individual molecules. Discover how heat changes the rate of a reaction, but doesn't change the amount of salt that is dissolved, with help from a science teacher and field biologist in this free video on chemistry.

Part of the Video Series: Chemistry & Biology
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Video Transcript

Hi I'm Brian with Today we're going to discuss how hot water dissolves salt. So the main reaction here that's going on or the main interaction that's going on deals with the breaking of different bonds and then weak bonds or interactions forming between the individual molecules. So we're going to look at what salt, what the bonds of salt and water actually look like and then how they interact and then later we'll discuss what heat might do to factor into the equation. So first, salt as we know it, table salt is such sodium and chlorine. And it's these two elements form ionic bonds with each other which means the electrons are shared unequally. Sodium gives up an electron making it positively charged and the chlorine accepts that electron making it negatively charged. So salt is really just a combination of sodium and chlorine ions that are connected into solid structures. Water on the other hand is a type of covalent bond which means that the electrons are shared and it's a polar molecule so the electrons are shared unequally. Oxygen tends to really like electrons and hydrogen really doesn't hold onto it's electrons too strongly. So the oxygen tends to hog the electrons a bit more in that bond and the net result is that the part of the molecule with the oxygen tends to be partially positively, or partially negatively charged, I'm sorry, and the hydrogen part is partially positively charged because it's given up it's electrons. So now what happens between the two is you have your positively charged sodium and that interacts with the partially negative parts of water, so the oxygen end. And then at the same time, the chlorine ions interact with the partially positive hydrogen water and by interacting with water, the salt ends up being pulled apart and thus dissolves. So heat is just a measure of the amount of kinetic energy in a system and as you increase heat, there's more energy. So you're going to increase the speed at which all these molecules are traveling and interacting. The odd thing about salt is that by increasing the heat, you do increase the rate but you don't change the amount of salt that can actually dissolve in a solution. So heat increases the process but doesn't change how much salt can dissolve. This has been a brief discussion of how salt dissolves in water and heat's impacts on the dissolving.


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