Task 4 FAQs

Please contact us to let us know you’re working on the taskWe will contact you right away with any breaking news.

Announcement: Teams need to submit three 100-mL samples of their treated water for testing(the original task stated the amount as one 100 mL)

Task 4: Fluoride Treatment and Removal

Q1: We have not been able to get our calcium sulfate to dissolve. What should we do?

A1: We have not had any trouble getting our sample to dissolve, but if you continue to have difficulty, the suggestion below may help.

The task statement says that the test solution will contain 1.7 grams of calcium sulfate per liter of solution.  According to the literature, the solubility of calcium sulfate in water at 20C is 0.2 grams/100 ml of water (solubilities are always expressed as per 100 ml of water).  This translates to 2 grams/liter, which is more than the task calls for, so one would expect to be able to dissolve 1.7 grams per liter.  So I don’t know why you are having trouble getting it to dissolve.

One issue might be applying heat.  For many compounds, solubility decreases with increasing temperature, and calcium sulfate is one of them.  (It seems counter-intuitive, but that’s the way it is.)  Its solubility at 30C drops to 0.16 grams/100 ml.  You might be able to get it to dissolve by cooling the solution, say, in a refrigerator, and see what happens.  Letting it sit at room temperature may not be cool enough.


Q2: Is there a time limit on how long we can run our experiment?

A2: You may start running your experiment as soon as you are issued an on-site safety permit. The run-time may go until the sample is taken (1:30 PM on Tuesday).

We begin issuing permits around 7:00 pm on Sunday evening, after the Safety meeting and finish for the evening at 8:15 PM. We continue issuing the permits on Monday between 8 am and noon. Priority is first given to teams that have their ESPs approved prior to arrival at the contest, and next, to teams in the order in which they sign up (your team will sign up for a permit inspection when your bench-scale is completely set up).


Q3. Is there a requirement for all 5 gallons to be run through the column before taking the sample?

A3: No. We do not anticipate that your team will need all 18 liters of synthetic solution. We provide more than enough to ensure that you do not need to come ask for more while you are running your bench-scale demonstration.




Please check back regularly for more FAQs.