Density Lab Day 5: Layering all 4 liquids

The layered liquids

There are some regular "Friday " things that we do, so this left about half the period for the activities so it was a perfect day to let the students layer all the liquids in one test tube. One mistake I made is I did not habe them write their "final" prediction (from yesterdays whiteboard) in their lab notebook.  As a result they had to remember their prediction from yesterday.

The students had to get thbeir supplies and pour the liquids in.  the "prediction" piece is turning out to be a problem because it strengthens the notion that the layers have to do with the order you place them.  some groups predicted wrong and saw the liquids sink und other liquids.  (some of the justifications are precious...because its stronger or because i poured it wrong)  I even saw one group pour the red in before the blue and the yellow and they still got the "correct" layering.  I tried to point out that everyone in the room has the same layers, and in p2, i even showed them what would happen if you put yellow on the bottom, then green, then blue, then red.

I asked them " why did this happen?" and eventually I got density out of them (it is the unit we are on after all!).  Then I said that you can quantify density and asked for prediction (more than, less than) about the density of the liquids.

3rd period, I did not mention their predictions and just said tho add the liquids into the test tube.  this lead to more liquids sinking under other liquids, hopefully leading to them understanding that the order does not matter. Their is the exception of the red and the blue.  I talked briefly about how some fluids mix and some do not (referring to the salad dressing) and tried not to dwell on it.  this only happened to 2 groups, one group, the blue/red layer sunk under the yellow , leaving a small pinkish layer on top. I pointed out that (almost) everyone got the same layers, and asked why.  again, thickness came up and I was able to provide evidence against that because the yellow (thicker) goes on top of the blue (thinner).  When density came up i treated it as a possibility and discussed how we can quantify density and suggested that as possible rout we would want to follow...to gather the evidence for that theory.

I did the "Question of the Day" towards the end of class (after the layering activity above).  Today we did a quick-write, meaning the students write for four minutes straight in a given topic.  The topic was "what do you think about this weeks activities/labs?  What did you like? What would you change? What did you learn?  Below are 2 typical examples.  Note the use of the word "thicker".

I talked with Marie and we agreed that a more natural flow would be to have the students measure the density of the 4 liquids they have been working on.  ( the "poster" says to find the density of the mystery liquids...salt water and baby oil?).  Monday I will do that.