seven-layer-columnA few weeks ago on my 9News segment I featured a Seven-Layer Density column. It’s a colorful way to talk about density in the classroom. Well… we thought we had all of our facts straight, but when we inadvertently put in the experiment write-up that oil and water don’t mix because they have different densities, my email box was flooded with concerned teachers, parents, administrators and more, who wanted to set the record straight. Yes, it’s true, oil and water don’t mix because of their intermolecular polarity, not because of density. I love when people actually get involved with the experiments we are posting and care enough about the information to let me know when it isn’t quite up to par.

So, we had our density problem solved, it would seem the Seven-Layer column had experience its fifteen minutes of fame, but, no… this one just wouldn’t die. The day after my news segment, some of our staff noticed that the vegetable oil and rubbing alcohol layers had switched places! Knowing the great response we received before, we opened it up to our readers for their thoughts on what was happening with our column. Posted below is what you had to say…

15 replies
  1. Cheryl
    Cheryl says:

    As the alcohol in the alcohol solution evaporates what is left is water. This will eventually make the alcohol solution sink down to the water level. Of course by this time the alcohol solution won’t really be alcohol but water. So these are my thoughts on the seven layer density experiment. BTW my daughter did something very similar to this for her science project a few years ago. She had bystanders figure out solution was which by looking at the chart for density and seeing which solutions sank and which settled higher.

    Reply
  2. Mike
    Mike says:

    Likely water has been absorbed by the alcohol layer.
    So the question is how to test this hypothesis?
    We could use a small pipet to remove part of the alcohol layer and measure the density, but we already know the density changed.
    Perhaps we could the color change of cobalt chloride (red = water, blue = no water). I think some silica packing still has the color crystals
    to show this change.

    Reply
  3. Madelon
    Madelon says:

    It would seem the only way for the alcohol to change positions would be for it to change density……if something could be added or subtracted the density could change. If the alcohol is actually a mixture of alcohol and water, then the water and the alcohol could be evaporating from the mixture at different rates, that could change the density. That’s my hypothesis.

    Reply
  4. Ali
    Ali says:

    Hi, I just read about the alcohol and vegetable oils switching spots in your density demo. I am not sure this is a guess, but alcohol evaporates at a faster rate than many other liquids, right? I believe the carbon can’t bond to the hydrogen (not sure if that is exactly right, I thought I read that once somewhere), therefore the gas component in it is evaporating. If that’s the case, wouldn’t the liquid being left behind be more compact and have a heavier density?

    Hope I’m not totally off base, if I am I will need to get a rag to wipe the egg off of my face…lol. I’d love to know the answer.

    Reply
  5. Joe
    Joe says:

    Try putting just vegetable oil and rubbing alcohol in a column and then capping the column. The idea here is to exclude water. I think some water may be diffusing into the rubbing alcohol which is usually a 70% solution of isopropyl alcohol in water, and increasing the density slightly.

    I think you should rethink your opening statement “Everyone knows that vegetable oil and water don’t mix. That’s because the two liquids have different densities.” Oil and water don’t mix because they have different intermolecular forces and the oil molecules cannot force water molecules apart in order to mix. Alcohol and water have different densities and yet they mix quite well because they both rely mainly upon hydrogen bonding to hold them next to their neighbors.

    Reply
  6. Judith
    Judith says:

    OK, when you add alcohol and water, the alcohol fits in beween the water molecules, right? I wonder if the alcohol simply falls between the molecules of the other substances?

    When alcohol and water mix the resulting volume of the two solutions is less than the total of the individual volumes. In this case “one plus one” does not equal two. The reason for this decrease in volume can be attributed to the hydrogen bonds which develop between the alcohol molecules and the water molecules (See “Surface Tension of Water” to see a further explanation of hydrogen bonding). This hydrogen bond pulls the molecules really close to each other and the small water molecules will fit nicely in the spaces between the alcohol molecules.

    Having read the reference above, I have revised my thoughts. How about if the alcohol slips through each of the substance molecules, making temporary bonds as it passes down through the column?

    Reply
  7. Karen
    Karen says:

    Perhaps some of the vegetable oil dissolved into the rubbing alcohol, increasing the density of the new mixture enough that it became denser than the oil. Did something similar happen with the dawn or either sugar and the water layer?

    Reply
  8. Karin
    Karin says:

    Hello Spangler Team!!
    Just a quick thought on why the rubbing alcohol and vegetable oil may have changed places in your density column. Rubbing alcohol typically contains acetone, methyl isobutyl ketone, water and denaturants. Some of these compounds evaporate quickly (the acetone, for example) causing the rubbing alcohol itself to change. Since the major compound in rubbing alcohol is water, it makes sense that the density of the rubbing alcohol as it evaporates would change to be very close to the density of pure water (1.00) and making it more dense than the vegetable oil (density 0.91.)

    Keep the great ideas coming!!

    Reply
  9. Barb
    Barb says:

    My chemistry is quite old and rusty, but I do recall that alcohol loves to pick up water. Perhaps the alcohol is doing that slowly throught the oil layer, which would increase its density. That’s my guess.

    Reply
  10. Todd
    Todd says:

    I am curious…has the volume of either liquid changed? Specifically, is the same amount of oil present as was present before, or is there slightly less oil now then there was before? I’m not sure if it would even be measurable, actually, but If the level of the oil has lessened, that may support my theory, which is as follows and may be completely false:

    The alternative fuel known as E85 is a mixture of ethanol (grain alcohol) and petroleum distillates. The alcohol mixes with the petroleum and bonds to it, creating a slightly more dense, higher-octane fuel. I am curious if perhaps the isopropyl alcohol behaved similarly with some amount of the vegetable oil, bonding to it and creating a denser alcohol/oil mix overall mix, in essence “sinking” the oil/alcohol mix below the remaining pure oil.

    This may be WAAAAAYYYYYYY off, but who knows?

    Reply
  11. amber
    amber says:

    I am desperately trying to help my 7 year old with her science project that I thought would be fairly easy… Guess again. I have never completed a science project in my life. My childhood was a disaster but I am trying to help her.

    I searched and searched for something I thought would be easy to do. To test changes in density of water and how it affects the floatability of an egg.

    Well I added salt and it floated,
    I added sugar it did not
    I added flour it did not
    I added veg oil and it did not.

    So far so good, but now I am trying to help her with her conclusion.

    The only thing we noticed is that the salt seemed to blend into and mix real well into the water, I think this actually changed the density of the water and thats why it worked.

    The sugar didnt mix quite as well and particles were floating to the bottom no matter how much I stirred it, so my guess is maybe this isnt affecting the density as much as I thought it would.

    The flour just made the water cloudy, chunky and ultimately particles floated to the bottom.

    Now the oil, it surely didnt mix at all with the water. It stayed completely on top, it only stuck to the egg when I pulled it out but it in no way made the egg float.

    So my question is, would it be an intelligent answer for her to say that her conclusion is that these other items didnt mix into the water and therefore didnt affect its density???

    When we did her hypothesis she felt the egg would float in all of them because “she thought it would make the water thicker” and it did make it thicker so in that sense of the word the density has changed, right? Oh please help me. I pray someone is listening tonight because I am supposed to turn this in tomorrow morning…

    I really thought this was going to be a no brainer… I guess that speaks volumnes in itself…

    Any smart people out there… please help… Ill be up all night… LOL

    Reply
  12. waleed
    waleed says:

    i want to ask here what will happen if we add alcohol to the water in different concentrations do we have two separated layers and which one is high density and which one is low density .

    Reply

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