Reef Chemistry Question of the Day #147 Heat Dissipation

[Randy Holmes-Farley]

Reef Chemistry Question of the Day [HASHTAG]#147[/HASHTAG]

You come back from vacation to find your alkalinity doser ran out of supplement and the alkalinity is 5 dKH.

In a hurry to make a new batch of alkalinity supplement, you heat a mixture of sodium carbonate and RO/DI water almost to boiling to try to speed the dissolution.

You then realize, however, that you do not want to add the very hot liquid to your doser. You consider three options to cool it for 30 minutes prior to adding it.

Which of the following results in the lowest temperature of the liquid after 30 minutes? In all cases, imagine that it is in a glass container on your kitchen counter and your kitchen is at 70 degrees Fahrenheit.

A. Add one 10 mL ice cube to it, then wait 30 minutes.
B. Wait 15 minutes, then add one 10 mL ice cube which melts within 5 minutes.
C. Wait 25 minutes, then add one 10 mL ice cube which melts within 5 minutes.
D. Just wait 30 minutes.

Total time to measurement is 30 minutes in all cases.

Good luck!






















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[DrayB]

place the container in cold water and change the cold water every few minutes is what i would do....but my answer is c

 

[AllSignsPointToFish]

Do you wait an additional 10 minutes on option B after the cube melts? The premise is for a 30-minute cooling period, but option B doesn't explicitly state an additional cooling period after the cube melts.

 

[wcharon]

I will use option D because you shouldn't raise ALK fast. Also, i was on vacation for several days so the waiting of 30 min will not affect more that was already affected.

Just my 2 cents...

 

[Randy Holmes-Farley]

Do you wait an additional 10 minutes on option B after the cube melts? The premise is for a 30-minute cooling period, but option B doesn't explicitly state an additional cooling period after the cube melts.

I clarified in the question that the total time in all cases is 30 minutes.

 

[jgraz]

Option D

 

[Lenny_S]

Option C
The hotter the liquid compared to the ambient temperature the faster it will cool. By waiting 25 minutes then adding the ice you get the maximum cooling.

 

[redfishbluefish]

Wait one minute! This isn't chemistry.....it's calculus. Boy did I hate calculus....actually the crappy teachers I had. Why can't most math teachers teach? (Sorry to the good ones.)

This one reminds me of the coffee question on one of our exams.....to have the hottest coffee, when do you add the cream? Immediately, when the coffee is poured, or ten minutes later when you're ready to drink it?

Anyway, for the coolest liquid, add the icecube 25 minutes later.....answer C. And if this a "regular" one gallon mix (3785 mls), I surmise (Yes, I've forgot the actually calculus), that 10 ml ice cube will only slightly drop the temperature.

 

[Randy Holmes-Farley]

This one reminds me of the coffee question on one of our exams.....to have the hottest coffee, when do you add the cream? Immediately, when the coffee is poured, or ten minutes later when you're ready to drink it?

The fact that I switched it to a supplement makes it reef chemistry.

 

[heatdissipation]

Thought you were talking to me personally.

 

[heatdissipation]

After 30 minutes I would assume that all options would end up at 70 degrees. But it would depend on how much solution you started with. Would take a lot longer for a gallon to cool than a cup

 

[BNUTTHEHUT]

A

 

[Randy Holmes-Farley]

Thought you were talking to me personally.

I was.

 

[beaslbob]

d

less work and won't precipitate anything.

 

[beaslbob]

Even better just add it to your sump. small amount of hot water will not do anything except very local effects.

 

[zemuss]

Unless your adding multiple ice cubes don't know that just one in any time frame would help.

Also if this ice cube is made with regular water, than your risking cooper getting added to the alk solution.

So D would be my answer

 

[redfishbluefish]

The fact that I switched it to a supplement makes it reef chemistry.

Randy, I stand corrected....you are right....this does make it a chemistry question.

As a matter of fact, as I gave it more thought, it was my local barista who asked the question about cooling coffee. Interestingly, he did want me to include all work and calculations. Boy it sure is tough getting a good cup of coffee these days.....by the time I did all the calculations, my coffee was cold!

 

[beaslbob]

wouldn't it be better to not heat the water to begin with?

Or even just add the sodium carbonate to the sump?

 

[beaslbob]

as long as all the ice melts how does the mixture cool down? None of the heat is exported any faster then if you just did nothing and the mixture cooled down from ambient temperature. Plus the amount of ice is very small compared to the total solution.

Putting the container in ice would suck the heat out of the container and solution.

Putting enough ice to double or triple the solution would lower the average temperature. But again as long as all the ice melted the final temperature should be the same. only the final temperature would be lower then if you hadn't added the ice.

 

[beaslbob]

can we ignore the evaporative effect of condensate on the outside of the container?