Reef Chemistry Question of the Day #276 Evaporation of Organic Carbon Dosing Products

[Randy Holmes-Farley]

Time for a new chemistry question of the day.

Working late one evening, you accidentally left your DIY organic carbon dosing solution uncovered. Note: you live in Arizona and the air is very dry.

By the time you discovered it, some had evaporated.

It initially contained a mixture of 150 mL of vodka (providing ethanol) and 750 mL of vinegar (providing acetic acid).

Compared to the initial mixture, the concentrations of the organics in the remaining solution is most likely to be:

1. Higher in ethanol and higher in acetic acid
2. Higher in ethanol and unchanged in acetic acid
3. Higher in ethanol and lower in acetic acid
4. Unchanged in ethanol and higher in acetic acid
5. Unchanged in ethanol and in acetic acid
6. Unchanged in ethanol and lower in acetic acid
7. Lower in ethanol and higher in acetic acid
8. Lower in ethanol and unchanged in acetic acid
9. Lower in ethanol and in acetic acid

Good luck!


Previous question of the day:

Reef Chemistry Question of the Day #275 Effect of Underwater Pressure on a Balloon

Reef Chemistry Question of the Day #275 Yesterday was a pressure question, so let's go with another... Suppose that you diving on a reef and are 100 feet below the surface. You fill an ordinary latex party balloon with a small amount of air from your tank, expanding it to far less volume than...

www.reef2reef.com

 

[thatmanMIKEson]

No Google i pick Number one...only water evaporates and leaves every other substance more concentrated..? Thats a tuff one with so many multiple choice!


Wait I've also thought I heard one time that moonshine left with the lid off will get water inside and lower the proof..


I'm probably off completely, but I love the question, I can't wait to see the answer later!

Thanks randy, lay down some knowledge on us!

 

[FishTruck]

Ethanol evaporates fastest, then water, then acetic acid.

1. Lower in Ethanol, higher in acetic acid - number 7 is my guess.

 

[TriggersAmuck]

Lower in acetic acid and ethanol. How do I know? Because I extracted the ethanol and drank it trying to solve this problem, and in running out of vinegar while dosing my tank ticked off my wife enough that I had to find a replacement somewhere for cooking! Come to think of it, I'm not feeling too good...................
(But before I passed out I guessed that both would be lower in concentration, which takes a little bit of digging to come to that conclusion, possibly counterintuitive to our usual understanding of other dissolved substances, i.e. salt, which would increase in concentration).

 

[Pistondog]

7

 

[Borat]

7. Lower in ethanol and higher in acetic acid

 

[PeterC99]

What if I didn’t do too well in High School chemistry? I’m still trying to master mixing saltwater.

 

[Pistondog]

7. Lower in ethanol and higher in acetic acid

High 5

 

[Borat]

High 5

5 high!

 

[thatmanMIKEson]

High 5

Only 4 min to change your mind? Whats your hypothesis?

Everyone sounds like they get it but me!

 

[ColoredRock]

Ethanol evaporates fastest

even with the lid on... I dont think my parents bought that one tho when I was growing up.

 

[Azedenkae]

7. Lower in ethanol and higher in acetic acid

 

[moz71]

I agree on the lower ethanol higher acid. Funny as I was getting to the very bottom of bottle my nitrates all of a sudden started rising. Are there certain bacteria that likes one over another Randy? As I am thinking this may have happened.

 

[Bruce Burnett]

9. lower ethanol and lower acetic acid as they both evaporate faster than water.

 

[lubeck]

6

 

[NowGlazeIT]

8?

 

[Reefcare1]

8

 

[Randy Holmes-Farley]

Great job, folks, many people got this one.

And the answer is...

Compared to the initial mixture, the concentrations of the organics in the remaining solution is most likely to be:

7. Lower in ethanol and higher in acetic acid

While it is not always a perfect way to determine the answer, in this case, simply looking at the relative boiling points tells us the relative order of vapor pressure at a given temp, and hence the relative rates of evaporation.

The boiling points are:

Ethanol: 78 C or 173 F
Water: 100 C or 212 F
Acetic Acid: 118 C or 245 F

Thus, when the lid is open, ethanol is coming off faster than water which is coming off faster than acetic acid.

Consequently, the concentration of ethanol is lowering and the concentration of acetic acid is rising relative to the total volume (or relative to the water).

 

[moz71]

Great job, folks, many people got this one.

And the answer is...

Compared to the initial mixture, the concentrations of the organics in the remaining solution is most likely to be:

7. Lower in ethanol and higher in acetic acid

While it is not always a perfect way to determine the answer, in this case, simply looking at the relative boiling points tells us the relative order of vapor pressure at a given temp, and hence the relative rates of evaporation.

The boiling points are:

Ethanol: 78 C or 173 F
Water: 100 C or 212 F
Acetic Acid: 118 C or 245 F

Thus, when the lid is open, ethanol is coming off faster than water which is coming off faster than acetic acid.

Consequently, the concentration of ethanol is lowering and the concentration of acetic acid is rising relative to the total volume (or relative to the water).

Randy thanks so much! I posted a question in my answer but probably didn't see it. I am at the bottom of one of my bottles and notices the nitrates rising again, do certain bacteria feed off each (ethonol and acid) ? wondering if the evaporation caused the nopx working less effectively because the mixture changed?

 

[Bruce Burnett]

Great job, folks, many people got this one.

And the answer is...

Compared to the initial mixture, the concentrations of the organics in the remaining solution is most likely to be:

7. Lower in ethanol and higher in acetic acid

While it is not always a perfect way to determine the answer, in this case, simply looking at the relative boiling points tells us the relative order of vapor pressure at a given temp, and hence the relative rates of evaporation.

The boiling points are:

Ethanol: 78 C or 173 F
Water: 100 C or 212 F
Acetic Acid: 118 C or 245 F

Thus, when the lid is open, ethanol is coming off faster than water which is coming off faster than acetic acid.

Consequently, the concentration of ethanol is lowering and the concentration of acetic acid is rising relative to the total volume (or relative to the water).

Ok I get that, I am not a chemist but my understanding is acetic acid has a mild affinity to hydrogen and at room temp the difference in evaporation of vinegar and water is negligible but long term aetic acid will be higher concentration. Which still makes your statement correct and my answer wrong.