Help with failed science experiment

[onlyzombiecat]

Dd and attempted an experiment last night and it did not work the way it was supposed to. What did we do wrong?

"Polluting the duck pond"
materials-
small plastic bag and fastener
wax paper, cut into small pieces
felt tip pen
large pan or bowl of water
liquid detergent

Stuff bag with waxed paper pieces. Close bag with fastener.
Draw duck on bag.
Float duck in water.
Add a little detergent.

The duck is supposed to sink (showing that getting detergent in a pond or lake is very bad for ducks).
Our duck would not sink.

I used a store brand liquid dishwashing detergent that claims to be comparable to Dawn. Our water was cool. We added a little detergent to the water and nothing happened. We stirred it in. We added a little more and waited awhile and nothing happened. We added more wax paper to the bag and put it back in the water. We poked at the bag. We applied detergent directly on the bag/duck.
The water was pretty soapy by the time we gave up but the duck still floated.

ETA-
We tried not having the bag tightly closed. We pushed the bag completely under water.
The explanation in the book of why the bag would sink states "The wax paper and plastic are water repellent- just the way a live duck is...a detergent enables water to stick to greasy materials."

[Ruthla]

A plastic bag is going to float in soapy or plain water. However, a wax paper duck will float in plain water for a little while, but sink rapidly in soapy water- the wax on the paper is similar to the waxy coating on duck feathers.

I don't understand why the instructions had you filling a plastic bag, rather than making an origami duck out of waxed paper. Maybe the bag was supposed to NOT be leakproof, so the water gets into the bag either way but the waxed paper keeps the water out of the baggie? Maybe you had the opening on top rather than sitting in the water?

I'd try it again without the plastic baggie, but rather use wax paper by itself to create something ball-shaped- either origami folding, or shape it into a hollow ball and seal with tape, etc.

[Malva]

You should try out different combos with your dd.

Figuring out what went wrong with an experiment is often more interesting than following instructions and getting the expected result.

[onlyzombiecat]

Thanks for the advice.

[Delicateflower]

Originally Posted by Malva

You should try out different combos with your dd.

Figuring out what went wrong with an experiment is often more interesting than following instructions and getting the expected result.

:

The most important part of science is "why?"

[PJsmomma]

I also tell my son that if an experiment fails we learn something too!

You can write it on an observation sheet and then add to it when you try again.

[lezzliet]

Hello,

My son is working on this same experiment for his science fair.  It is not working for us either.  Did you ever get it to work?  How??!! :)

Thank you for any help you can give!

Leslie

[onlyzombiecat]

We gave up and moved on to something else because dd wasn't interested.

I hope someone out there has done it successfully and can tell you how.

[moominmamma]

The "experiment" makes no sense. Plastic bags float partly because they are hydrophobic and repel water, but mostly because they are less dense than water. Detergent will overcome the hydrophobicity, but it won't do anything to change the density. I agree that a wax-paper origami duck would have made more sense to use.

Besides, detergents aren't harmful to ducks because they make them sink -- which seems to be what this demonstration is implying. Typically detergents cause problems for ducks because they alter the chemistry of the water (eg. by adding phosphates) in such a way that they encourage the growth of plants (eutrophication), resulting in algal blooms, decreasing dissolved oxygen as the higher biomass of algae decomposed, with the lower oxygen levels eventually leading to reductions in plant and animal populations that the ducks feed on.

Miranda

[zebra15]

what moom says plus what others have said- the reasons for doing experiments is not to get the 'right' answer but to figure out what is going on and possible other solutions.

Originally Posted by moominmamma 

The "experiment" makes no sense. Plastic bags float partly because they are hydrophobic and repel water, but mostly because they are less dense than water. Detergent will overcome the hydrophobicity, but it won't do anything to change the density. I agree that a wax-paper origami duck would have made more sense to use.

Besides, detergents aren't harmful to ducks because they make them sink -- which seems to be what this demonstration is implying. Typically detergents cause problems for ducks because they alter the chemistry of the water (eg. by adding phosphates) in such a way that they encourage the growth of plants (eutrophication), resulting in algal blooms, decreasing dissolved oxygen as the higher biomass of algae decomposed, with the lower oxygen levels eventually leading to reductions in plant and animal populations that the ducks feed on.

Miranda