Reef Chemistry Question of the Day #282: Temperature Effects on Parameters

[Dburr1014]

3 and 4

 

[Rkdunn1]

Reef Chemistry Question of the Day #282

Suppose your coral reef aquarium is chugging along nicely at 80 degrees F.

You withdraw a sample to run some tests, and the temperature drops to 72 degree F before you are ready.

Which of the following parameters will NOT have changed as the temperature changes from 80 to 72 degrees F (only considering the temp change, not anything else that may be happening, such as gas exchange with the air). Note that any change meets the question criteria. For example, an alk change from 7.4 dKH to 7.401 will count, even if it might still be written as 7.4 dKH.

1. Nitrate at 8 ppm
2. The salinity at 35 ppt
3. pH at 8.1
4. Alkalinity at 7.4 dKH

You can pick more than one answer. At least one is correct (no change at all) and at least one is wrong (will change to some extent).

Good luck and don't be shy guessing. This is not an easy one.

Previous question of the day:

Reef Chemistry Question of the Day #281: Alkalinity You May Not See

Reef Chemistry Question of the Day 281 All of the following are incorporated into commercial supplements. Which of the following will not boost alkalinity in a normal reef tank with regular dosing? 1. Calcium acetate 2. Calcium formate 3. Calcium polygluconate 4. Calcium carbonate 5. Calcium...

www.reef2reef.com

Nitrate..

 

[lubeck]

Nitrate doesn’t change. Salinity and ph def change with temperature. I would say alk would change ever so slightly

 

[Randy Holmes-Farley]

For those who have recently replied and may not have seen my answer on an earlier page, it is in the link below.

Reef Chemistry Question of the Day #282: Temperature Effects on Parameters

There are two - SG for salinity and ppt for Alkalinity. EDIT: ppm* not ppt :grinning-face-with-sweat: There’s also meq/L for alkalinity lol

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[AJsReef]

Thanks for the read Randy , interesting stuff!

 

[Kieran McBride]

Continuing the discussion.

3. pH at 8.1


pH does change with temperature. All aqueous fluids do, and potentially to different extents. This effect is in addition to the temperature compensation that pH meters can do and often allow users to dial in. That correction is a correction of the probe response itself to the actual pH. But the actual pH also changes.

One main reason is that all acids and bases in the water will change strength to some extent as temp changes. Even water. In totally pure water, it breaks apart into H+ and OH-,

H2O <---> H+ + OH-

and in totally pure water at about 25 deg C, the concentration of H+ (and OH-) is about 10-7 moles/L. That is how the pH (the negative logarithm of the H+ concentration) of totally pure water comes out as pH 7.

As the temperature is raised, the concentration of H+ and OH- increases (the equation above shifts to the right, probably driven by entropy, being higher on the right with 2 ions vs one molecule on the left, since higher temps favor the higher entropy side of chemical equilibria, but I've not verified that expectation of mine in this particular circumstance). Thus, the pH declines (H+ rises) as temps rise even though the water is not any more acidic (having equal H+ and OH-).

In seawater, there are other acids and bases involved, complicating matters further. Bicarbonate, carbonate, carbonic acid, borate and boric acid, etc. All of these contribute to small changes in pH with temperature of seawater, even with nothing entering or leaving the water.

The exact, summed together and measured changes can be found in the scientific literature if folks are interested.

The temperature dependence of pH in surface seawater

The temperature dependence of pH in surface seawater was investigated as a function of salinity and CO2 composition using the most recent values for t…

www.sciencedirect.com

Taking all this into consideration, how are ICP tests conducted? If I'm not mistaken it's a high temperature plasma solution/gas or whatever the term may be called during the process. Does this process change the actual value of any of the elements being tested or is it even significant enough to be concerned about?

 

[Randy Holmes-Farley]

Taking all this into consideration, how are ICP tests conducted? If I'm not mistaken it's a high temperature plasma solution/gas or whatever the term may be called during the process. Does this process change the actual value of any of the elements being tested or is it even significant enough to be concerned about?

Icp sucks the fluid into the plasma zone. Everything present is broken down into individual elements that are then detected either by the light they emit, or by mass in a mass spectrometer.

They are quantified by comparison to a fluid with a known concentration of the same elements.

The temperature of the fluid being sucked in will have a small effect on the total ions in the volume that gets into the plasma , but as long as the sample and standard are at the same temperature, it won’t appreciably matter what the temperature is.