Theoritical questions for chemists

[Eyore]

http://www.seafriends.org.nz/oceano/seawater.htm#composition

i put this link up to illustrate what i am getting at

of interest to me is the mmol x valence "statement" and it infering the values are correct. lets ignore the fluoride value lol

1. if i calculate the respective values for a salt (eg potassium chloride or calcium chloride), i find the values for anion and cation to be almost equal.

so my question- i am summising (i believe correctly), that actually the respective mmol x valence to be exsactly equal, and the reason it doesnt calculate exsactly is simply because the molar masses are abbreviated?

in which case does any body have a link which has full molar masses to a lengthier decimal?

I also think its fair to say that the statement " the fact the above values for seawater are very close to a zero value for mmol x valence promotes it must be close to correct" is utter rubbish! because infact you could throw whatever you want in and a zero value will be reached? The same applies to balling recipes in terms of ionic balance ( at the point it is inputted)

consequently is it fair to say then that these "seawater calculators" are to all intents and purposes a theoritical balance of ions and realistically little more, ie its theory not tested??

so what about minor elements measured in picogrammes /litre?? this bit does baffle me, i assume its not tested at those levels, so where do the figured come from for these trace elements?

my last question is regarding impurity in balling salts
if i am correct regarding the salt being perfect anion and cation balance, the same would apply to the impurities i imagine?? so lead would be present with the correct amount of sulphate or chloride?? etc etc

feel free to criticise lol

i am no chemist, but my maths forces me to question these things

[disc1]

Charge balance MUST be maintained. It's the law you know.

If you want more accurate molar masses, google "Periodic Table of Elements" and take your pick. There are literally thousands of different copies of that table on the web. Find the one with the best molar masses and have at it.

[toothybugs]

^^ That, or get more up to date on your sacrifices to the water gods.

Your pick :)

[Randy Holmes-Farley]

As David mentions, there's no way for there to be a significant anion/cation imbalance in seawater.

Of course, there can be huge imbalances among the anions or among the cations. The biggest one that gets messed up easily and which we do not monitor is the chloride to sulfate ratio.

As to the balance, the exact measurements of the ion concentrations will be much more variable than is reflected in the tables of seawater averages. Never are all of them measured on the same sample, so they tie back to total chloride or to total salinity (usually measured by conductivity).

FWIW, many of the ions do not carry the charge one might think. The balance still works out, but, for example, only a small fraction of the carbonate is present as free carbonate. Most of it is ion paired to magnesium (dissolved MgCO3), calcium (dissolved CaCO3), or sodium (NaCO3-).

Also, the charge on many ions varies with pH. Borate, for example.

The table also completely lacks entries for hydroxide, carbonate and H+.

[Eyore]

i think then my assumptions are correct, as david says charge balance must be maintained

i will search for better period tables, the last time i did this the usual molar masses (ie 4 zeros past the decimal) were what i found

i am assuming i am right also in terms of values we use- ie tje figures are shall we say "tweaked" in order that theoretically it adds up

the only question remaining is the minor traces- how do we get these values? is it really tested at sub 0.0000001 mg/l levels?

[Randy Holmes-Farley]

Yes, it must be maintained, at least within those sorts of numbers. Static charge and such messes with that requirement, however. One could charge up a small amount of seawater, but it would be unstable.

FWIW, I doubt anyone tweaked it to add up to zero net charge.

Rather, they collect analyses from lots of researchers to get values for the different ions, corrected for the salinity or chlorinity of the sample actually tested.

Yes, the trace elements are really detected at those low levels, and it can be very challenging, both technically and preventing impurities from the glass ware, etc, from overpowering the low seawater values.

[Eyore]

thanks randy

thanks all

[Randy Holmes-Farley]

You're welcome.

Happy Reefing. :)