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Topic: Sodium Fluoride, Calcium Carbonate, and Citric Acid  (Read 1713 times)

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Offline k8.jackson

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Sodium Fluoride, Calcium Carbonate, and Citric Acid
« on: October 05, 2018, 09:29:51 PM »
I am in high school doing an experiment in which I am using limestone (calcium carbonate) to remove fluoride from water. I am creating fluoride concentrations of 10mg/liter, 5mg/liter, and 1.5mg/liter to replicated different concentrations found in drinking water in different areas. However, at such low concentrations I read that calcium carbonate is not very effective at removing fluoride from water so I was planning on using citric acid to create more Ca+ activity. However, for some reason the citric acid messes with the reagents which I use to test fluoride concentrations and the readings suddenly double or triple to amounts that are simply impossible.

First, does anyone have any recommendations as to what to use instead of citric acid that will not affect the reagents (I couldn't find out what the reagents are, but here is the link to where I purchased them: https://hannainst.com/hi739-26-fluoride-high-range-checker-reagents.html). Second, but perhaps more importantly, my friend told me that the combination of these chemicals is creating hydrofluoric acid. I doubt this because I am not using any chemicals like sulfuric acid, however I have little experience in chemistry and I do not want to accidentally create such an acid.

Offline Borek

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Re: Sodium Fluoride, Calcium Carbonate, and Citric Acid
« Reply #1 on: October 06, 2018, 03:39:26 AM »
Citric acid lowers the pH, which can easily interfere with the reagent. Any other acid that will increase solubility of lime will have exactly the same effect.

Low pH and presence of fluorides makes a solution equivalent to solution of hydrofluoric acid (doesn't matter where the ions come from), so there is a grain of truth to what your friend told you. However, at concentrations you are working with I wouldn't worry much.

Sadly, can't help much more, idiots at hannainst site decided to redirect me to my national site without asking me whether I wan't it, or not, so I don't see your page, just the main page :( Perhaps someone located in US will have more luck.
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Offline chenbeier

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Re: Sodium Fluoride, Calcium Carbonate, and Citric Acid
« Reply #2 on: October 06, 2018, 03:49:02 AM »
I am in high school doing an experiment in which I am using limestone (calcium carbonate) to remove fluoride from water. I am creating fluoride concentrations of 10mg/liter, 5mg/liter, and 1.5mg/liter to replicated different concentrations found in drinking water in different areas. However, at such low concentrations I read that calcium carbonate is not very effective at removing fluoride from water so I was planning on using citric acid to create more Ca+ activity. However, for some reason the citric acid messes with the reagents which I use to test fluoride concentrations and the readings suddenly double or triple to amounts that are simply impossible.

First, does anyone have any recommendations as to what to use instead of citric acid that will not affect the reagents (I couldn't find out what the reagents are, but here is the link to where I purchased them: https://hannainst.com/hi739-26-fluoride-high-range-checker-reagents.html). Second, but perhaps more importantly, my friend told me that the combination of these chemicals is creating hydrofluoric acid. I doubt this because I am not using any chemicals like sulfuric acid, however I have little experience in chemistry and I do not want to accidentally create such an acid.

The chemical what you are purchased are standards with different concentration of sodium flourid and a buffer system (TISAB) what is used for ionic sensitive electrodes. So do you have a ISE Electrode for Fluoride?
And one thing is clear pH has an influence.
To precipitate Flouride its better to use calcium chloride.

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