hey everyone section 417 we are almost done we are going to be talking about indicators you've used them a couple times in the titrations that we've done indicators basically change color at a certain range and there are a lot of different types of indicators and I'm going to give you just an introduction to them on this video in the next few minutes then we'll go into a bit more detail about them in class tomorrow and in groups in nutshell an indicator consists of two things it consists of a weak acid and it's conjugate base it's it's pair the indicators that are very broad I'm just going to use the symbols I and for indicator so HD is the weak acid or the acid form of the indicators and the base form is IND D minus it's conjugate base it differs by an H+ what makes indicators so special is that the weak acid and the weak base have different colors this could be yellow and this could be blue so whatever form is dominant that's the color that you see if you have more hi n d then you will be yellow if you have more I and D minus then you will be blue so this right here is the fundamental idea of today this is an indicator period an indicator is an equilibrium mixture between a weak acid and its conjugate base that are different colors so this is a weak acid ionizing in water to produce h3o+ and its conjugate base which is in D and the weak acid and its conjugate base are different colors in this case yellow and red if you have more IND D minus if you've shift shed this thing left then you are going to be yellow if you shift this thing right then you are going to be red so whatever way this indicator is shifted that's the color that you see so let's look at that in a bit more detail one more thing if you are 100% in the middle so you're not shifted left and you're not shifted right you're exactly in the middle you have equal parts yellow and red then you will be orange okay welcome to elementary school with the primary and secondary colors yellow and red make orange so you're yellow if you've shifted way left you're red if you've shifted way right and if you're exactly in the middle then you are orange and that's a special uh scenario which we'll get to later called the transition point so how do you shift these things left or right well again here is our overall indicator H IND D indd minus if we add an acid we increase the concentration of h3o it's going to shift left to undo our change and this thing is going to dominate we're going to make more of that and it's going to turn that color maybe it's yellow if I can shift this thing right then I will well how do I do that well to shift it right I need to add a base when I add a base h3o plus is going to decrease in concentration and equili is going to shift right to make more of it and in essence make more h n d minus which will be red so when I add a base it's going to turn red because equilibrium is Shifting right so we have a list of indicators and we can figure out what colors they are at different PHS so if you look on your indicator chart in your data booklet you probably don't have that in front of you I'm just going to pretend you're looking for that right now if you look up Brum crestle green you're going to see it as a um acid form and a base form um you're going to see it uh on one side of the chart at a certain range of a pH on the other side of certain pH so if you add a drop of HCL the acid form of that indicator is going to be present okay and it says in the chart it's going to be yellow if you add a base NaOH well then the base form of the indicator is going to be present and that chart tells us that it's blue so the acid form of Brum Crystal green is yellow the base form of Bram cestal green is blue and what's exactly halfway well yellow and blue makes green your kindergarten teacher will be very proud of you okay there's literally 12 indicators that we're just going to be playing around with what's the acid form what's the color of that what's the base form and what's the color of that what's in the middle is is your mixture that middle point like I said 30 seconds ago has a very specific name it's called the transition point the transition point is when you have equal parts acid form and base form of the indicator and that's molarities the concentrations of those are the same so if you look up on your acid base chart for methyl violet Bram crestle green and indigo Carmine you will see they're all yellows and blues and halfway between a yellow and blue will be green so 99% of our questions will be looking at colors what color is methyl violet in an acidic solution with that certain pH what color is Bram cestal green in a certain pH and what color is indal carbon in a certain pH but there's unfortunately one kicker it's never as simple as you always think it's going to be there's one little special scenario that can occur if you were to write out a Ka expression which you can because this is a weak acid Ka are products over reactants coefficients are exponents and you ignore liquids and solids well if I D equals h d you can cancel those off from your expression when you cancel those off from your expression you get Ka equals h3o well that's just weird what am I where am I going with this well at the transition point of an indicator the KA equals the concentration of h3o well we know this number okay this marity can be calculated which means we can now calculate the kaas of indicators so we're going to do that we're going to actually not do that on the video we're going to do that in class tomorrow because I want to repeat this you can calculate the KA of an indicator so we are going to stop right here make sure you understand that indicators are equilibrium mixtures of weak acids and weak bases with different colors you can shift that equilibrium left and right and that is what changes the color and that's the color that you see that's the end of that section there ladies and gentlemen we'll see everyone tomorrow