Auto-Ionization

mhm. Now water can react with another water molecule in a process called self ionization or auto ionization. In the process we create H 30. Plus. So hydro nia my on and O H minus hydroxide ion here, one water molecule act as an acid while the other one acts as a base following Bronston Laurie theory acids donate H plus. So this acid donates an H plus. In the process the water becomes O. H minus because it's lost in H Plus, charged ions exist as acquis species within water plus the water. The other water accepts an H plus and becomes H +30 plus a quiz. Now this is the actual reaction that two water molecules reacting with one another to create those two products. Now we can simplify this by just simply saying we have water as a liquid and then we have the creation of H plus ion And O. H.. In reality the water molecule isn't splitting into these ions because that's not how water works. This is just a simplified explanation of what's occurring. Now from these two equations, we should realize that H plus and H +30 plus are equal to one another. The same exact thing H plus is just a simplified representation of the hydro name ion of H +30. Plus, we're going to say here that with these equations, we can talk about an equilibrium expression here, we're gonna say the equilibrium constant for water is called the ion product constant or simply kw just like all other equilibrium constants and equals products over react ints. So whether we're looking at the first equation or the second equation, it really doesn't matter. So in both its products overreacting remember we ignore solids and liquids within our equilibrium expression here we have liquid. So they would be ignored. Here's the liquids that would be ignored. Um If we look at the simple fly simplified reaction, we ignored this liquid. So reactions wouldn't be taken into account at all. So K. W just simply breaks down to just equal to products so it'll be equal to H plus concentration times O H minus concentration. So this is how we get the development of this equation here because of this equation we can draw on comparisons and calculations dealing with H plus concentration and O H minus concentration. If we know one we know the other because K. W. R. I on product constant will serve as a constant within our calculations. Now. With most calculations we're gonna be dealing with it under normal or laboratory conditions. So that means the temperature will be 25 degrees Celsius at 25 degrees Celsius. K. W is 1.0 times 10 to the negative 14 of value. You need to commit to memory now like all other equilibrium constants. It's susceptible to changes when we manipulate the temperature. So K. W just like all other equilibrium constants is heavily temperature dependent. You change the temperature, you'll change with the new kW value will be um If they do change the temperature they would have to give you a new K. W value because there's no way of really knowing. The only temperature that you're supposed to remember is at 25 degrees Celsius. This is the established value for K. W. And remember K. W. Is what connects my hydro knee um ion concentration to my hydroxide ion concentration. Taking these into account will attend to do the two example questions left on the bottom of the page. So click on to the next video and see how I approach example one in terms of relating K W two H plus and O. H minus.

So here it states at zero degrees Celsius. The kw four neutral solution is recorded as 1.2 times 10 to the negative 15 based on what you've reviewed, what can be said in terms of KW And the solution. All right. So, we know that K W is temperature dependent. Like we said up above, we know that at 25 degrees Celsius KW equals 1.0 times 10 to the -14. And here they just told us at 0°C KW equals 1.2 times 10 to the -15. Alright, so if we just think about this neutral solution, so think of it as we have H 20 liquid plus H two a liquid these guys would react with with one another under auto ionization or self ionization to produce H 30 plus acquis and O h minus a quiz Here, the temperature is increasing from 0 to 25°C or temperature increased according to the Chandeliers principle. It states that if we increase our temperature we shift away from heat And here are KW goes from 10 to the negative 15 to 10 to the -14. So our KW has increased K W just like all other case cap, equilibrium constant case is equal to products. Overreact ints So if your kW is increasing, that must mean you're producing more products. So we're gonna say here, if you're kW is increasing its because products are favored. Yes. Okay. And the only way products can be favorite as if we're moving towards them. So we're moving this way towards my products, causing them to increase and again, according to the Chancellor's principle, if we increase the temperature, we're gonna shift away from heat since we're shifting to the right. That must mean that heat is here on the left and if heat is a reactant, that means heat is being absorbed. So this would be an indo thermic process. So, again, this is taking what we've learned in terms of assets and bases in reference to KW. But applying concepts we've seen before with chandeliers principle, again, increasing temperature, decreasing temperature means we're going to apply the rules we've learned about the chandeliers principal looking to seeing if KW increases or decreases, just helps to determine which direction the reaction is shifting. But we still have to apply what we've learned in terms of the chandeliers principle to find out if our reaction is truly exotic, thermic or endo thermic. And recall that what I've said in earlier videos when we're talking about thermal neutral, that means that delta H will be equal to zero. There'd be no real change in temperature and therefore there would be no shifting left or right because you're KW or all equilibrium constants would not change under thermal neutral conditions. And we know that we have enough information to answer the question, we determined it was endo thermic not exa thermic. So based on what we've learned thus far. Look to see if you can attempt example too, if you get stuck, don't worry, just click onto the next video and see how I approach that same question.

So here it states determine the concentration of hydrogen ions for pure water at 50 degrees Celsius. Here again, temperature is changing. So R. K. W will be different from what we're used to seeing Kw now is 5.3 times 10 to the negative 14. Because again, kw is temperature dependent. Changing the temperature changes K. W. From the common number of 1.0 times 10 to negative 14 to a new value. Now here they're telling us that we have pure water. Pure water means that it is neutral, neutral water means that O. H minus concentration is equal to H plus concentration. And since we don't know what either one is, you say they're both equal to ax. They're connected by the equation of KW equals H plus or H +30 plus are the same thing times O. H minus. So both of them are equal to X. So X times X. Gives us X squared And they're both equal to this new value for K. W. since the temperature is not 25°C. So that's 5.3 times 10 to the -14. We're looking for the hydro knee um ion concentration which is H plus. So we just need to isolate X. So take the square root of both sides here when we do that, that's gonna give me my concentration for X. So when I do that I get X equals 2.30 times 10 to the negative seven moller. So since it's neutral, this would be the concentration of H plus as well as O. H minus in this question. But remember at 25 degrees Celsius, K. W. Is 1.0 times 10 to the negative 14. Once you change the temperature, it becomes a brand new value. You'd be given that new value. The only one that you need to memorize is the one at 25 degrees Celsius. So just remember the connection between hydrogen ions and hydroxide ion in in reference in relationship to on the ion um product constant of KW.