Science Buddies: "Ask an Expert"

Hi - My daughter is doing the carbon filtration project using granular activated carbon and powdered activated carbon.

She has followed the experimental procedure but the results were not as she expected. Through her research she assumed that the granular activated carbon would remove some contaminants but not as much as the powdered activated carbon would. The results were that with both food color concentrations after using the granular filter, the color of the water changed slightly but rather than getting "lighter", it seems slightly darker and less "clear"/murky. This is most evident with the zero contaminent water which went from clear to slightly darker - it appears from mixing with the carbon.

Is she doing something incorrectly? She used 4 layers of coffee filters as recommended and that doesn't seem to be the issue since the powered carbon filter results were excellent and as expected for the different contaminent concentration types.

To troubleshoot, she tried to double the amount of granular activated carbon from 3grams to 6grams and redid the experience - thinking that increasing the total amount of surface area of carbon in contact with the water would have different results. However, the results were somewhat the same...the color of the water changed but to the naked eye it seems less "clear" and murky which gives it a darker hue.

Any advice you can provide would be extremely appreciated since this doesn't seem to be the expected result that the water would become "more contaminated" after using a granular carbon filter? We also only purchased a limited amount of materials so there is only so many more trials she can conduct before running out of materials and time.

Thank you in advance.

[Administrator note - project directions: https://www.sciencebuddies.org/science- ... king-water ]

Hello,

This sounds like a fun project! I love how your daughter has already revised her hypothesis based on her first round of results and conducted another experiment with more carbon!

I have not don’t this experiment myself but I’m wondering if there may be an issue with the coffee filters. Any chance they are overflowing or not fine enough to prevent the powdered carbon from passing through? Alternatively, could powdered carbon be getting into the bottom of the cups as you are preparing them and the mixing with your filtered solution?

Hope this helps!

Audrey