Create multicolored, three-layer density columns in test tubes using sugar, water, and food dyes.
This video is part of the Flinn Scientific Best Practices for Teaching Chemistry Video Series, a collection of over 125 hours of free professional development training for chemistry teachers - elearning.flinnsci.com
ATTENTION: This demonstration is intended for and should only be performed by certified science instructors in a safe laboratory/classroom setting.
video Transcription
as we've gone through the course we try to do a lot of different experiments many experiments were really forced to tell the students exactly what to do very scripted almost what sometimes will be referred to as a cookbook type of experiment and there are very valid safety reasons why we want to know exactly what the students are doing at any given time but there are times I think in chemistry where we can hope in things up of the buzz words might be inquiry or open-ended problem-based whatever term you want to use with this the idea is there a way that we can pose a problem to the students that forces them to apply their understanding of the chemistry concept to solve a problem to produce something forcing her students to think in the chemistry lab it's a very challenging it aspect because they're perfectly comfortable in many cases uh... simply checking off a series of steps that they followed and they may not know why step six happens after step five but they're just following a recipe in the end everything turns out well if they follow the directions well this experiment what I call the test tube challenge will break that mold it requires very little into in the where in terms of worrying about chemistry pick chemicals we're talking about using sugar water in food coloring sugar water and food coloring that's all that they were really need in terms of the chemicals given the price of sugar you're buying five pounds of it on your way into school probably that day you've got plenty of sugar the food coloring not a problem tap water available in most rooms without too much difficulty when my students would come in they might see something such as this on the front demo table and they might saying hey you how did you make that and responses yes so uh... you're not if you've got a chemistry textbook that has the classic density gradient you know the one with the mercury at the bottom in the bolt that's floating I’ll refer to that picture maybe have a picture like that quite a transparency and say take a look at that while sinking floating a density type of gradient but what I try to do is to perhaps show them something like this and then say candidate produce something similar but not being a large graduated cylinder in a test tube now what I’ve discovered many students who are honors level students struggle with the idea of applying the concepts they can manipulate the math they can solve for any missing variable but putting them in open-ended situation and their out of their comfort zone the last very nicely things like so how much sugar did you put in the bottom layer wool aren't you can answer my question all my gosh help can you be math teacher and not answer questions it's important to win over your students it's important to acknowledge please do not ask how white made that because I’m not going to tell you and asking you nicely and they will try multiple times stick to your guns are not going to answer that question what the students are told I want three clear distinct layers day-old blue yellow bread don't care about the colors themselves but it makes sense not to go wad read uh... but you could go blue yellow blue were however you want but I need three liquid layers inside it s too you can you show ger water food coloring and any quickness in your lab drawer anything you guys want to use now that's the open-ended problem but I want you to picture in your mind what can happen if you try to do this open-ended problem if your class like mine can accommodate twenty eight students we typically do experiments with fourteen sets of lab partners ait cannot accommodate fourteen sets of how do you do this coming at me all twice and so I have taken on at the system were al arrange the kids around the room in seven groups of four by can he handle seven sets of questions coming at me I can monitor seven groups of four there are signs of the groups they're showing this showgirl water food coloring I need three liquid layers no solids presence in your final test two at least where I teach many times students like to form larger groups especially on thinking activities you'll have the corporate merger this group of four people suddenly start talking to that group before suddenly you have no why is that the on one side an alliance of eight on the other and then you've got the pdf four kids that you've assigned to a group that maybe they're not even talking to each other they're just hoping to wait out the storm but we work on this tomorrow if nobody gets it if you're fortunate enough to be double blocked I can remember looking out and telling him you have approximately eighty three minutes to go began in terms of the timing so I’ve got seven groups of for strategically placed around the room you can use the lab stations nearest you and here's how we're going to keep them working in a group before what we say in my class we're going to go plus three plus two plus one what that means is the first group to successfully finish with three liquid layers in a test tube three points extra credit for everybody in that group and then they've got a front proceed to the show or they watched the other group still struggle they've got the second group to finish two points extra credit for everybody the third group one point extra credit with seven groups again talking teacher here three of the seven groups art should be thinking we're going to get extra credit on this is on some and one of these thinking type of challenges cut they help migrate the very last group all cash where that's so smart group where the challenge group we can't you can still get a ten out of ten but you're racing against the clock and now you're down to eighty one minutes to go you're racing against the clock you're competing against the other groups for the extra credit but the very last group can still get it ten out of ten so again it should not hurt their grade nafta group gives up well that's a whole nother story but my job once they know what's expected is did know jim along the way and do what i have to do for instance asking questions like while your top layer injured middle layer are mixing how much sugar did you put in the bottom layer and they might say ten grams and if they use the same amount of work sit ten grams around the bottom layer to grahams are in the middle ware and then how much is in the top one gram so the one graham in the two graham layers are mixing okay steelhead ten a lot of they needed to and then you get one in the top two layers how did used to typically these students will self correct only gosh why did we use that we probably are my gosh we had ten in the bottom are we will require are we required to use sugar in everywhere no artist sugar water food coloring ten grams zero grams one graham once we get zero five ten once they figured that out it is a glorious day in the bracken world when you watch them poor and they pour with such emotion that the layers can still mix became shakir pollute we're teaching persistence were teaching problem solving remember i'm walking around the room saying you can use anything you want you let me know if you need the centrifuge i've got the centrifuge i've got microscopes from biology i've gotten a respects available they quickly learned we don't actually need them stopwatch is alright here sometimes you'll have kids run up cuz remember it's plus three plus two plus one i don't know why but i'm getting a stopwatch i am going to stop the other faculty king although stopwatch is tonight i don't know why we need he wouldn't put it out if we do need it right yes he would starring routes if they need them if they're not in the lab drawer i have other equipment that is available do we have to ask you for yes you do and it might be hidden behind the demo table all right joe that's a really good question starring roger behind the demo table go back to their intake why don't you just put a no 'cause every group past ask for it because i'm not just telling them what they need the most critical thing other than beakers test tubes grown meyer flasks the pipette so important to their success and their overall happiness but i will not as i've done here have the equipment that they need out for them they've seen means they've worked with these it's their job perhaps it's already in the lab drawer uh... there we go if a group if i look up and i still have maybe five minutes to go in the group is just on the verge of imploding because they haven't been successful a nice hint say it to the std to the group is heyyy because used everything in your lab drawer i wasn't sure if i got a everything in the lab for the u_s_ might need open up the labs work for a half all my gosh you guys we need an hydroponic which people even get on my car being the main there a minute away from cranking it out now it might seem like and given them all the answers what's amazing is that the plus three plus two plus one concept they're gonna work within your group they're not going to remember the hint like so how much sugar you're putting in each player on my gosh yeah now i understand also so they take tremendous pride in in giving being able to think through a problem and solve it fastest inside had do this something like ten minutes but i'm not gonna tell my students that i'll tell them that the all-time bracken record his twenty one minutes what that guys if you think about it they know that they want to hurry but it also tells them of all the groups that he's had do this the fastest once took twenty one minutes that immediately tells them he's expecting us to take some time on this that that puts them at the s and are able to go after it be ok did we set the new world record with nine and a half minute i think so uh... yeah i'd while in and did not come back the next day did anybody beat our time of nine and a half minutes yesterday in your other classes uh... noel nobody get uh... that that's awesome so they're they're very very proud of their creativity in their problem solving as something that you do have to be aware of when you do it open ended lab like this you're not going to perhaps get the most beautiful results and that's to be expected they are in its very typical in in science brain chemistry we may say hey we made aspirin we were the first ones in the world to make it and we made it in four percent yield k but we crossed the finish line first we're number one typically what happens the group's who then say it while so that works can tweet tweet get and make it better they might give you in eighty percent yield but they're not gonna be the first ones so what i love is the group that gets plus three plus two plus one those groups tend not to make the most beautiful bing bing bing it's like jerry at dane little tiny bang and then adding again when you go me that's three layers you guys are the first ones and so the seventh group the seventh group before at the last ones to finish desires the best-looking one of second period are walking yes three equally spaced lawyers still ten out of ten we'll win the best-looking test two uh... category for our class so i really encourage it it will bring it up a little bit sugar water and food coloring very inexpensive starting materials uh... it is a tremendous amount of time here's one way to actually make it and i want you to think about possibly in your own classroom compare we can given the cookbook version you could probably time that you say the wall finishing eighteen and a half minutes why because they're all following the exact same set of directions there's not as much making if you tell them for instance zero grams of sugar into ten milliliters add five grams of sugar into ten mil leaders and ten grams of sugar into ten milliliters of water there's not a lot of thinking involved to give you an idea i've watched students tried the cookbook approach my first year of teaching that's the way i did it what some of them did is they work i added the ten grams of sugar home no handed red food coloring to act dump it out but says it needs to be blue it's not the students' fault they're not able to distinguish what is important with what is not important and sometimes what we've been following the honors kids who were the ones who are going to get it right would immediately dump that out because they're saying it's not gonna look right in it's not going to work because it needs to be blue on the bottom the student who may never sold for the missing variable properly probably has the ability to look at that and so it doesn't really matter what color it is it simply just to show the different layers so i'm glad you having to be the referee within the group where they had this discussion and and the weaker student is saying okay i may not be able to calculate the density of those three but i know first i wanna use an i drop ur and legal yes because the understands will calculate the density values they will because they've done again steve liquids lab courage if you don't calculate devoutly against students who don't even bring a calculator to class for drawing right here's what i'm this deal uh... i'm going to take the stuff with the most sugar and i'm gonna put that in and again there's not a lot of thinking involved if this is how we're doing i'm gonna go to the medium density and again let them figure out at its slowly and drop twice let them figure it out trooper water and food coloring when i'm hoping to create is a classroom where they view the lab idea is a parcel it's not an illustration of density work every single density gradient looks the same because they take a tremendous amount of pride even in checking back the next day hated it all mix and if you've ever had the misfortune of thinking you're gonna teach something on monday that they'll remember on tuesday and they show up acting as if they weren't even there an activity that they actually remember the second day and you think while i didn't even know that you would remember doing it in your check wanting to check to see if it's mixed so here we go with me third layer there while the students are working on this i do like to play music in my classroom and i think music and do a number of things that can really late in the mood when the race is on tenia breaks up the new silence and this or that i love the plays by the archie sugar sugar um... and and boy i'll tell you what i would go to any of the uh... online things itunes whatever you want and search under sugar or sweet and the fact that you thought i had kenneth dot music for the event uh... in many cases has has my students is thinking as this like your entire life and how did you actually come up yes and know where you're going to struggle and i've got the soundtrack available for the experimental my gosh uh... but we do win him over we're gonna win them over in the matter unit and this activity which does its heavy on the thinking make no mistake about it uh... many times teachers when they try this will say ponder this'll take five minutes and winds up taking fifteen minutes because again it's possible to do it you saw i mean you could even say let me make the three solutions for the students in advance if you want to take five minutes and you want to do all look the same there's a way to do that but i really think there's real value and letting them deep figure out the importance of the layering the amount of sugar the food coloring it's probably best not to have read and read and read it uh... that they've got i think a little bit about what colors they wanna use uh... lots and lots of fun it's also important to compliment them especially if you held uh... some low achieving students the students as you assign the kids to the seven different groups the student that you hoped would participate and if that student contributed in really lead their group you know the surprise while i wasn't sure that whittle johnny was going to be able to do this and johnny was the thinker of the group that students is going to get a phone call that night and i can tell you it'll terrified their parents all my gosh teacher called our house little johnny will say i never had a teacher colour house before thought for sure i got in trouble was i suspended or what they do no well jenny wild his entire group and i'll tell you what it solely september and i cannot wait to see what johnnie can do when the chemistry class gets harder that one minute phone call two or three years later after they've div no longer have your class or in some cases ten years later hey mister bracken in a graduation party mister bracken member when you called my house after that test-tube thing with the layers that scared by parents so much that is the only time anybody's ever called my house for a positive thing if you do that if you can catch your students doing something right you own them they will do anything you can get in the hardest open-ended problem and their confidence is sky-high and builders do whatever you ask them so i would encourage you to keep that in mind even is that post lab type of thing anne ten minutes to make some phone calls tonight about the uh... the ones who really surprising self test tube challenger fun fine density open-ended type of lab activity
