Reef Chemistry Question of the Day #165 Salinity of Skimmate

[Taservices]

Seeing as my skimmate isn't even remotely translucent and as far as I'm aware a skimmer won't remove ionic material (except of course the tiny amount of salt in the water that spills over, but that's not the point), I'll have to say conductivity would be the best measure.

Haha, Cory I just noticed. We Grande Prairie folk love our chemistry questions XD

 

[SROPE]

I'll say #2.

 

[TCFletch]

That was a trick question!

 

[Randy Holmes-Farley]

That was a trick question!

Why is it a trick?

 

[beaslbob]

It's always a trick when you don't know the answer

 

[Habib(Salifert)]

None of them. One is IMO the far least worst but then still, a priori, partly inaccurate assumptions would have to be made.

 

[toaster77]

the "salinity" should be very low because ideally skimming should not remove strictly polar molecules such as ions. There will also be lots of insoluble stuff.

 

[Randy Holmes-Farley]

the "salinity" should be very low because ideally skimming should not remove strictly polar molecules such as ions. There will also be lots of insoluble stuff.

But skimmers remove water. Do you think it leaves salts behind?

 

[SROPE]

Could it be possible for them to leave salt behind?

 

[Randy Holmes-Farley]

Could it be possible for them to leave salt behind?

No.

 

[SROPE]

Too bad. I still say #2.

 

[toaster77]

the skimmate should have much higher concentration of organic compounds, certainly any water carried over will still have salts/ions esp through wet skimming. water could also evaporate from the skimmate leading to higher salinity. many of the organic compounds removed will have charges on them as well. the very hydrophobic organic compounds are more likely removed via carbon.

 

[JimWelsh]

None of them. One is IMO the far least worst but then still, a priori, partly inaccurate assumptions would have to be made.

I stand by my earlier answer, based on Randy being the grader of the test. That said, my initial reaction to the question was to wonder how one defines salinity in the context of a skimmate matrix, especially when some people skim quite relatively dry.

 

[cowboy]

I wanna go with conductivity but something keeps screaming hydrometer if you have enough volume, but for fun I wanna go with silver nitrate .1norm and potassium chromate. If my math is correct should be .1*35450****/volume. please correct me if the calculation wrong.

 

[cowboy]

.1*35450*amount of silver /volume for I didn't even think about what I was spelling when I put titration

 

[Randy Holmes-Farley]

And the answer is...2. Conductivity meter (IMO, I've not tried anything except this answer)

When I've seen results from several folks the result came out pretty close to the conductivity of the tank water, which makes sense, although it can also be evaporating and concentrating in the collection cup if you wait long enough. Most organics, even if charged, are too large to contribute significantly tot he conductivity in a seawater-like solution. Even acetate (about the smallest charged organic likely to be present) contributes far less to conductivity than a chloride ion.

Also, organics in a salt solution, whether particles or dissolved molecules, don't reduce conductivity all that much. The ions easily travel around them, unless the concentration of organics is very high. Inorganic particles will behave similarly, not impacting the answer much.

So if the goal is to measure salts in the water, I think a conductivity meter would likely work best.

As to the others...

The dissolved organics in the water will perturb the refractive index and potentially lead to an off reading by a refractometer. Particulates will scatter the light, making the "line" harder to see and less well defined. The color and light scattering may make it hard to see through it at all, depending on the concentration.

A hydrometer will be impacted by the effect of the organics (both dissolved and particulate) and particulate inorganics on liquid density. How big the effect is will, obviously depend on the concentration and what exactly is in the liquid.

Weighing will be off due to the weight of the organics and the inorganic particulates. If you burned off the organics and corrected for lost inorganics as you would for seawater, you still have the problem of inorganic particulates, such as silica and calcium carbonate.

Happy Reefing!

 

[Randy Holmes-Farley]

.1*35450*amount of silver /volume for I didn't even think about what I was spelling when I put titration

That might work, assuming that you could see the endpoint, and that you assumed that the skimmate has about the same relationship between chlorinity and salinity that seawater does.

 

[cowboy]

That's where I am unsure I do not have any formal chemistry training but what I do have is 10 yrs dealing with cement, acid, and water analysis. So with that said I'm really enjoying trying to figure more of the chemistry side of things out. I truely welcome any feed back on an answer that I may give that is wrong. I do welcome any criticism that anyone may be able to provide.

 

[TCFletch]

It's always a trick when you don't know the answer

There should have been a 5th option: "All of the above"

 

[Randy Holmes-Farley]

There should have been a 5th option: "All of the above"

Then you'd be wrong picking it.