WCLN Titrations Involving Precipitation Reactions Chemistry

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Titrating a sample unknown chloride ion concentration with silver nitrate of known concentration provides a method of finding the chloride ion concentration in the sample. How this titration works is explained here. • http://www.BCLearningNetwork.com. • 0:00titrations can be used to determine the concentration of a specific ion in a • 0:09sample solution you will see how titrations involving precipitation • 0:13reactions work here is a setup for a titration of a solution with an unknown • 0:18concentration of co- or chloride ions this long tube is called a beer at your • 0:25it can also be spelled vur ete this valve called the stopcock is close to • 0:32keep the liquid in the beer at when it's opened lickable grip or flow out of the • 0:37bottom of the burette in this example the burette is filled with . 100 molar • 0:43silver nitrate solution the solution in the beer ad is called the standard • 0:48solution the standard solution has a known concentration in this case is . • 0:54100 molar AGL three standard solution can also be called the titrant in this • 1:01hydration a solution containing chloride ions is added to an Erlenmeyer flask and • 1:07placed under the pier at the solution in the flask is called the sample it's the • 1:14solution with the unknown concentration it can also be called the analyt because • 1:20this solution is being analyzed to find out the concentration of chloride ions • 1:24in it in this titration a few drops of sodium chromate solution are added to • 1:29the solution the sodium chromate solution is known as an indicator in • 1:35this titration it will change color and what is called the endpoint of the • 1:39titration will show you how all of this works will focus on the solutions will • 1:46dissociate AG no.3 into its individual ions which are ag+ and no.3 minus • 1:53science the nitrate ion does not form any precipitates it's a spectator ion • 1:59here so let's delete it from our discussion and tidy up a bit so you can • 2:05think of the solution in the beer at as a source of AG plus four silver ions in • 2:11a titration we briefly open the store • 2:13car the solution in the burette drips into the flask bringing AG plus ions • 2:19with it • 2:25let's take a closer look at what happens in the flask and silver ions are added • 2:30to it now we've zoomed into the flask silver ions preferentially bond to • 2:37chloride ions rather than chrome a diet • 2:40this forms the precipitate silver chloride because silver chloride is • 2:47white the solution turns to a milky yellow color • 2:53as silver ions are added some will temporarily bond to the chromate ions • 3:03this will form the precipitate a g2 cro for or silver chromate silver chromate • 3:10is reddish brown so the solution will turn a slightly reddish color but silver • 3:18preferentially bond with fluoride so as the flask is shaken the silver ions will • 3:24leave the chromate ion and bond with available chloride ions and the radish • 3:29color will go away the solution will turn red momentarily as more Silver's • 3:36added but as long as chloride is still present shaking the flask will make the • 3:41red color disappear added silver ions will continue to bond with remaining • 3:47chloride ions at a certain point all of the available chloride ions have bonded • 3:53with the silver ions since there are no chloride ions left any silver ions are • 3:59added will have to bond to the chrome a diets • 4:05the formation of silver chrome a precipitate will cause the solution to • 4:09turn red again at this point when the flask is shaken the red color will no • 4:16longer disappear • 4:18there are no chloride ions available so the silver will have to remain bonded • 4:22with the chromate we say the solution has turned a slight permanent reddish • 4:27color this is what's called the endpoint of the titration a permanent color • 4:32change of the indicator signals the end point of a titration the equivalence • 4:39point for stoichiometric point of this titration is the point where the moles • 4:43of AG plus added to the flask is equal to the moles of co- that were in the • 4:49original solution in the flat in most titrations if the proper indicator is • 4:55used and the technique is good the equivalence point and the end point are • 5:00very close and they can be assumed to be the same . once we reach the end . we

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