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Chemistry Determining the concentration of ions in ppm

  • Thread starter rwooduk
  • Start date
729
47
Homework Statement
It's in a paper I am reading (not homework)
Homework Equations
ppm = (mass of solute ÷ mass of solution x 1,000,000
I'm a little confused by a basic statement in a paper I am reading. It says that calcium chloride (1 M) and sodium carbonate (1 M) i.e. equimolar, have "a predetermined concentration of 3500 ppm of Ca2+"...

Untitled.png


I understand that the mixing of these two will cause a precipitation reaction, but don't understand how the ppm of calcium ions was determined, was it measured / calculated somehow? Why would there be Ca2+ in the sodium carbonate solution? The statement seems a little confusing.

Thank you in advance for any help understanding this.

EDIT paper is Calcium carbonate scale formation in pipes: effect of flow rates, temperature, and malic acid as additives on the mass and morphology of the scale
 

mjc123

Science Advisor
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It says they are equimolar; that is the molar concentrations of sodium carbonate and calcium chloride are equal to each other; they are not necessarily equal to 1M. 3500ppm Ca2+ is 0.0875M. There is no Ca in the sodium carbonate solution - there can't be; the statement must mean that the (equal) molar concentration was chosen to give 3500ppm Ca2+ in the calcium chloride solution. It is a little awkwardly expressed, I agree.
 
729
47
It says they are equimolar; that is the molar concentrations of sodium carbonate and calcium chloride are equal to each other; they are not necessarily equal to 1M. 3500ppm Ca2+ is 0.0875M. There is no Ca in the sodium carbonate solution - there can't be; the statement must mean that the (equal) molar concentration was chosen to give 3500ppm Ca2+ in the calcium chloride solution. It is a little awkwardly expressed, I agree.
Thank you mjc. So, then I guess that the ppm was calculated by using the mass of calcium chloride required to give 1 M solution divided by the mass of solution, would that be correct?

Also, it says...

Untitled.png


So, that would be equimolar right?
 

mjc123

Science Advisor
846
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So, then I guess that the ppm was calculated by using the mass of calcium chloride required to give 1 M solution divided by the mass of solution, would that be correct?
No. First, it is ppm of calcium, not calcium chloride. Second, I have already told you that 3500 ppm Ca corresponds to a molarity of 0.0875M, not 1M.
So, that would be equimolar right?
Yes. You didn't tell us this before. Is there any more information you're hiding? It's not clear to me now what's going on, or what the 3500ppm refers to. It can't be the stock solutions if they are 1M. Are the stock solutions diluted before being mixed? Your quote suggests not. Is 3500ppm the concentration of Ca2+ after mixing the solutions? I wouldn't have thought so; CaCO3 is not that soluble. I'm really confused now.
 

DrClaude

Mentor
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Reference, please.
 
729
47
Apologies for the confusion and thank you for the further help with this. The paper is Calcium carbonate scale formation in pipes: effect of flow rates, temperature, and malic acid as additives on the mass and morphology of the scale

The excerpts from the paper which I uploaded as images are from Section 2.1.

 

mjc123

Science Advisor
846
394
Hmmm. It's still not quite clear. It looks like 3500 ppm is the concentration of Ca2+ in the mixed solution. The initial concentration would be 0.5M (20,000 ppm), and I would expect the concentration after complete precipitation to be lower than 3500, but this is a flow system, and deposition is slow, so maybe 3500 ppm is a dynamic steady-state value. They could have been clearer. (For example, the wording literally implies that the sodium carbonate solution was made from calcium chloride crystals!)
 
729
47
Hmmm. It's still not quite clear. It looks like 3500 ppm is the concentration of Ca2+ in the mixed solution. The initial concentration would be 0.5M (20,000 ppm), and I would expect the concentration after complete precipitation to be lower than 3500, but this is a flow system, and deposition is slow, so maybe 3500 ppm is a dynamic steady-state value. They could have been clearer. (For example, the wording literally implies that the sodium carbonate solution was made from calcium chloride crystals!)
Thanks mjc for taking the time to read the section of the paper. Yes, I was quite confused by their description. Your interpretation has been a great help. Thank you.
 

chemisttree

Science Advisor
Homework Helper
Gold Member
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Actually, the paper merely states that the test solution was prepared from a stock 1M solution to a final concentration of 3500 ppm Ca+2. That would mean that the test solution would be at 7000 ppm Ca+2 and the CO3-2 solution would be at whatever ppm CO3-2 would be equimolar with that.
 

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