WCLN Indicators How They Work Chemistry

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Introduction to Acid-Base Indicators • http://www.BCLearningNetwork.com. • 0:00acid-base indicators are added to • 0:04solutions and show specific color • 0:06changes as the ph of the solution • 0:08changes will start with an example • 0:10called methyl violet indicator when it's • 0:14added to a solution with the ph of zero • 0:16its color is yellow as we gradually • 0:19increase the pH from 0 to 1.6 the color • 0:23gradually changes from yellow to green • 0:25to blue • 0:28when we gradually increase the pH from • 0:301.6 all the way up to 14 the color • 0:34remains blue • 0:37so now we have a line down here join • 0:40that methyl violet changes gradually • 0:41from yellow to green to blue between 0 • 0:45and 1.6 and stays blue at ph is above • 0:481.6 • 0:51so now we'll start with the new • 0:52indicator orange for it is read at a ph • 0:55of 0 as we gradually increase the pH • 0:58from 0 to 1 point for the color stays • 1:02red • 1:05as we increase the pH from 1.4 2.8 the • 1:10color gradually changes from red to • 1:12orange to yellow • 1:15now we'll continue raising the ph we see • 1:18it remains yellow all the way up to 14 • 1:23we now have a line down here showing the • 1:25colors of orange for from ph 0 up to 14 • 1:31now we'll start with a new solution to • 1:33which we've added the indicator thymol • 1:35blue at ph 0 we see thymol blue as red • 1:39as we increase the pH up to 1.2 it • 1:43remains red • 1:45as we gradually increase the pH from 1.2 • 1:4822.8 the color changes from red orange • 1:53yellow • 1:54now will keep on increasing the pH from • 1:572.82 a it stays yellow • 2:01going from a 29.6 it changes from yellow • 2:05to green to blue • 2:07and going up from 9.6 214 it stays blue • 2:14so now we have a record of the many • 2:16color changes that final blue undergoes • 2:18as we change the pH from zero up to 14 • 2:23as well as records for orange for and • 2:25methyl violet • 2:27the acid-base indicator table you are • 2:29given contains the indicators we looked • 2:32at and quite a few more note how the • 2:34information on the table corresponds to • 2:37the colors on the diagrams • 2:42notice the colors of thymol blue at • 2:44lower ph's are near the top and those at • 2:48higher ph's are further down the table • 2:52let's look a little closer at a • 2:54particular indicator will use • 2:56bromothymol blue • 2:58the first color name is yellow this • 3:01means the color of brown family blue is • 3:03yellow if the ph is less than or equal • 3:06to 6 • 3:07the second color name is blue this means • 3:10the color of brown primal blue is blue • 3:12if the ph is greater than or equal to • 3:157.6 • 3:17the two numbers here give us the PH • 3:20range in which the color gradually • 3:22changes • 3:23so between six and seven point six the • 3:26color gradually changes from yellow at • 3:28six to blue at 7.6 halfway between six • 3:33and seven point six is 6.8 it is green • 3:36at 6.8 • 3:38most indicators are organic compounds • 3:41with complex structures here's the • 3:44structure of one form of the indicator • 3:46Rome some all blue • 3:48like all indicators bromothymol blue has • 3:51two different forms and acid form and a • 3:53base form • 3:55the acid form has one more proton and • 3:57the base form the difference is enough • 4:00to alter the structure of the molecule • 4:02enough to change its color • 4:04the two different forms are always • 4:06different colors here is the structure • 4:08of the acid form of braun tamil blue its • 4:11color is yellow • 4:13here's the structure for the base former • 4:15brawn thymol blue its color is blue • 4:19just save us from writing complex • 4:21formulas we can represent the formula of • 4:24the acid form of any indicator by the • 4:26simple generic formula hiin • 4:31and the formula of the base by the • 4:33simple generic formula i am- • 4:37and all indicators there is an • 4:38equilibrium involving a weak acid and a • 4:41weak base • 4:43the acid form of an indicator which will • 4:46call hiin is a weak acid the acid former • 4:50bromothymol blue is yellow but this is • 4:52not true for all indicators each • 4:54indicator has its own specific colors • 4:59the base form of an indicator is the • 5:01conjugate base of the acid form the base • 5:04form of the indicator broth I'm all blue • 5:06is blue

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