0 Members and 1 Guest are viewing this topic.

I work at a water bottling plant and I'm just trying to figure out how to test our mineral solutions. I'd appreciate it if anyone can help me with this one.One blend of water uses a sodium sulfate/sodium bicarbonate solution which is injected in RO water at a rate of .75ml per 1 gallon. The mineral solution is made of 96 gallons RO water, 30.72 lbs sodium sulfate and 50 lbs sodium bicarbonate. TDS on RO averages approx 0.8 ppm and the desired TDS on finished product is 12 - 18 ppm. What should the TDS on the mineral solution be to give me the desired result on finished product.

Just to clarify matters, Daltons don't enter into this problem as far as I can see.

84.01 molecular weight sodium bicarbonate,for a concentration at 9.92ppm, weight 370187.04064 grams. 142.04.Molecular weight sodium sulfate, for a concentraion at 6.08ppm, weight 383612.54144 grams.96 gallons uk, Ro water or 437 litres, plus 7.2 liters of soultion, total liquid volume 444.2 litres.

Looking at this another way, Daltons are stated to be one twelth of the atomic massso 84.01 / 12 gives you a dalton number of 7. for sodium bicarbonate,

What should the TDS on the mineral solution be to give me the desired result on finished product.

Quote from: hogied on 08/03/2011 08:26:13 What should the TDS on the mineral solution be to give me the desired result on finished product. So after two days my final answer which could be wrong and probably is, IS:-Your TDS should be for a gallon(uk) of RO water 642.65 grams:- with % ratios of 315.67 grams sodium bicarbonate at 62% and 327 grams sodium sulfate at 38%. Muliplied, that should give you a 96 gallon solution at 16ppm.

Looking at this another way, Daltons are stated to be one twelth of the atomic mass

QuoteLooking at this another way, Daltons are stated to be one twelth of the atomic massNo. Absolutely not. Everything you have written here is the result of a misunderstanding. I'll explain below.

Right. I'm going to go from absolute basics, and work up, to explain to Wybit what he's flailing about trying to understand... then if I get time I'll answer the OP...Firstly... each atom of a particular substance (hydrogen, carbon, uranium, lead, gold) has the same number of protons.Atoms also (mostly, except some hydrogens) contain neutrons. The exact number of neutrons may differ slightly, although not generally by very much. Neutrons and protons weigh, to a reasonable approximation, the same amount. Which makes the maths easier. The weight of an individual proton or neutron is (roughly) 1.66 x 10 ^{-27} kg. This unit of mass is known as a Dalton. So one proton weighs (roughly) 1 Da, one neutron also weighs (roughly) 1 Da. That's all a bit approximate, because, actually, the exact weights of protons and neutrons vary a tiny bit depending on what atom they're in. An atom of hydrogen my be hydrogen-1, hydrogen-2 or hydrogen-3, the atomic number (number of protons) is 1 in all cases, and there may be 0, 1 or 2 neutrons giving an atomic weight of (more or less) 1, 2 or 3 Da. An atom of carbon contains 6 protons, and 6, 7 or 8 neutrons. These are described respectively as carbon-12, carbon-13, and carbon-14 . The definition of the Dalton is 1/12 of the weight of one atom of carbon-12 (which is why I said all the other masses were approximate). Incidentally, weights are often expressed in grams/mole, where one mole of any substance is 6.022 x 10 ^{-22} atoms (or molecules). The mole is a number chosen such that that number of atoms of carbon-12, 1 mole of carbon-12, weighs 12 g. (And thus 1 mole of hydrogen gas, H_{2} weighs about 2 g).The molecular weight given on the periodic table for a particular element is the mass per mole.. it's an average number that tries to take into account the masses and abundances of the different naturally occurring isotopes of the element, thus chlorine is given as having a molecular weight of 35.5 because about 3/4 of naturally occuring chlorine atoms are chlorine-35, and the other quarter are chlorine-37.

Oh, and the original post.I assume that TDS is total dry solids

I was quoting a scientist I read that stated "one dalton was one twelth the molecular weight of a carbon atom"

That's really great, but how do you work out a dalton? You basically saving that 1 da is 1 au, or hyrdogen weights one dalton.If so what is the dalton for the sulfate and bicarbonate?

Rosy is the Dalton number for sodium bicarbonate 84?

QuoteI was quoting a scientist I read that stated "one dalton was one twelth the molecular weight of a carbon atom"Which was entirely accurate, but that's the definition of a Dalton, and only applies to carbon atoms.

QuoteThat's really great, but how do you work out a dalton? You basically saving that 1 da is 1 au, or hyrdogen weights one dalton.If so what is the dalton for the sulfate and bicarbonate?OK, firstly, you wouldn't describe it as "working out a Dalton", you'd describe it as "working out the molecular weight of the substance" (well, you would if I'm right about the question I think you're asking. But yes, plus-or-minus the exact definition, 1 Da = 1 a.u.So for sodium bicarbonate you'd work out the molecular weight as follows:Formula - NaHCO_{3}(So that's 1 atom of sodium, one each of hydrogen and carbon, and three of oxygen, per formula unit)I'm going to work in moles, because I'm a chemist and it's what I do... One mole of sodium has a mass of 22.99 gOne mole of hydrogen has a mass of 1.00 gOne mole of carbon has a mass of 12.01 gOne mole of oxygen has a mass of 16.00 gSo 22.99 + 1.00 + 12.01 + 3 * 16 = 84 g / moleEquivalently, one molecular formula's worth of sodium bicarbonate has a mass of 84 Daltons.I'll leave the other compound as an exercise for the reader.

I'm going to work in moles, because I'm a chemist and it's what I do... One mole of sodium has a mass of 22.99 gOne mole of hydrogen has a mass of 1.00 gOne mole of carbon has a mass of 12.01 g

One mole of oxygen has a mass of 16.00 gSo 22.99 + 1.00 + 12.01 + 3 * 16 = 84 g / moleEquivalently, one molecular formula's worth of sodium bicarbonate has a mass of 84 Daltons.I'll leave the other compound as an exercise for the reader.

You've been given the weight wanted, and there's no need to invoke the molecular weight or the molar concentration to do the calculation. You're making the whole thing unnecessarily complicated.

Ah, well no.. Sodium dodecyl sulfate is not the same as sodium sulfate. The correct formula for sodium sulfate is Na_{2}SO_{4}.Do you want to try again?

"This is a way of expressing very dilute concentrations of substances. Just as per cent means out of a hundred, so parts per million or ppm means out of a million. Usually describes the concentration of something in water or soil. One ppm is equivalent to 1 milligram of something per liter of water (mg/l) or 1 milligram of something per kilogram soil (mg/kg)."

Just quickly whilst I've got a moment:There are two ways of measuring concentration.. one is by weight-per-solvent, the other by molar concentration. Weight-per-volume is self explanatory, at least in principle. I think this is what is meant here, because it's the sort of thing you see written on the side of mineral water bottles. One ppm or part-per-million is one milligram of whatever the solid (or more generally solute) is per litre of water (since on litre of water weighs 1 kg, at room temperature), and one milligram is one millionth of a gram. So if the water contained 1 mg of sodium carbonate it would be one ppm sodium carbonate.

This is why I said originally that we didn't need to worry about the molecular weights to do the calculations.The molar concentration is to do (in effect) with the number of molecules (of whatever it is) in the solution. As I explained earlier, one mole of a substance is 6.02 x 10^{23} whatever the substance. And a molar concentration, a concentration of 1 M is 1 mole of the solute dissolved per litre. So if the molar mass of sodium bicarb is 84 g/mol, the mass of one mole of sodium bicarb is 84 g and to make a 1 M solution we'd put 84 g of sodium bicarbonate into a container, make up the volume to 1 L and bingo, a 1 M solution. A 1 mM solution has a concentration of 0.001 M (1/1000 of 1 M), so we'd use 84 mg or 0.084 g of sodium bicarb.

the molar mass of sodium bicarb is 84 g/mol

To make a 2 M solution of sodium hydroxide (Mw = 23 + 1 + 16 = 40) we'd use 2 x 40 = 80 g/L.Is this starting to make sense?

Could you give me a link to the calculator? Might help me explain what it's asking for!

16 ppm is only 16 mg if you're making 1 L of solution, because 1L water = 1 kg water = 100 g = 1,000,000 mg, so you've got 16 "parts solute" per million "parts solvent". If you're talking, as here, about mass-per-mass, you simply don't need to think about the molar concentration, and thus the molecular mass (in units of Daltons or any other unit) just doesn't come into it. There's no need to consider it.

100 g = 1,000,000 mg

The molar concentration is, numerically, completely different to the concentration expressed in ppm weight-for-weight. You're trying to conflate two unrelated things!

To make a 16 ppm solution, we take 16 mg of stuff, here sodium bicarb, and dissolve it in 1 L water (1000000 mg water).To make a 16 mM solution (millimolar, 0.001 M) we want 0.016 moles of sodium bicarb per litre. 1 mole of sodium bicarb has a mass of 84 g, so 84 x 0.016 = 1.34 g, we dissolve 1.34 g of sodium bicarbonate in our 1 L of water.

(millimolar, 0.001 M)

1 mole = 1000 millimoles, 1 millimole = 0.001 moles

"It's not me it's the calculator, it demands Daltons, I try to tell it, but it wont listen,"get a better calculator.OK, I guess I should have done this earlier before Wiybit wasted so much of his time.The question is "I work at a water bottling plant and I'm just trying to figure out how to test our mineral solutions. I'd appreciate it if anyone can help me with this one.One blend of water uses a sodium sulfate/sodium bicarbonate solution which is injected in RO water at a rate of .75ml per 1 gallon. The mineral solution is made of 96 gallons RO water, 30.72 lbs sodium sulfate and 50 lbs sodium bicarbonate. TDS on RO averages approx 0.8 ppm and the desired TDS on finished product is 12 - 18 ppm. What should the TDS on the mineral solution be to give me the desired result on finished product. "OK, the water starts with about 1 ppm of TDS and they want about 15 ppm so they need to add about 14 ppm.They plan to do that by adding 0.75 ml/ of solution per gallon.I guess its a US gallon. that's 3.79 litres.0.75 ml in 3.79 litres is a dilution of about 5050 to one so the solution added needs to be about 5050 times 14 ppmThat's about 7% w/vSo Just to check.Start with a solution containing 7% of whatever. That's 7 g in 100 ml or 7000 mg in 100 ml or 70 mg in 1 mlTake 0.75 ml of it so 52.5 mgDissolve that in 3.79 litres 13.85 mg/ litre i.e 13.85 ppmThere's already 0.8 mg/l present so that makes a total of 14.65 mg / litreThat's nicely in the middle of the range (12 to 18) they asked for.See, no Daltons and no moles. Barely any maths and certainly not several postings and several pages of stuff.If you want that in UK gallons then it's 7*4.54/3.79about 8.4%Of course, it depends on how you measure TDS too.

0.75 ml in 3.79 litres is a dilution of about 5050 to one so the solution added needs to be about 5050 times 14 ppm That's about 7% w/v

"One last thing the equasion I placed in my last post, what would that achieve in a uk gallon mix if you did it, in terms of ppm, adding 3.780 grams of sodium bicarbonate, what would that raise the ppm to, if it was plain RO water as I assumed, no ppm present?"OK3.78g in 1 gal3.78g in 4.54 litres0.83 g/litre830 milligrams/ litre830 ppmNot close.Why do you keep talking about daltons, molarities and moles?

Try the calculator here ...sorry, you cannot view external links. To see them, please REGISTER or LOGIN(It's the one you cited.)

Put in 3.78g in 1 Imp gallon and it tells you that it's about 800 ppm.Put any number you like in the molecular mass box ( and any units). It even gives the right answer in ppm when you put a negative molar mass (which is, of course, impossible) because it doesn't need to know it.