Sciencemadness Discussion Board

Chemical Testing Questions

carlrodeo - 13-8-2023 at 07:51

Hello. I want to test nitrate's (NaNO3) claimed purity of 99% and will test it following the poor man's test in liquid environment. Particularly in mineral water. Here's what needs to be done:

1. Using pipette draw 10 milliliters of water from 1000 milliliters water bottle and pour in a separate container
2. Mix 5 grams of NaNO3 in that container holding 10 milliliters of water
3 Return mixed solution to 1000 milliliter water bottle, close and shake
4. Draw 2 milliliters of water from that bottle and pour into new 1000 milliliter water bottle. Close and shake.
5. Using aquarium testing strips test for 10 PPM / 10mg/L


I wonder why it has to be 1000ml of water. There's PPM measurement in my equipment. The expected target result should match 10 PPM / 10 mg/L in color chart. Meaning if color is not as pronounced as it should be the purity of chemical is less than claimed.

Here are my questions regarding this method:

- Is there a reason why the amount of water has to be 1000ml? Will testing in for example 500ml of water provide not accurate result?

- Why 5 grams of chemical? Why not 3 grams or 20 grams?

- Would mixing 5 grams of chemical in 100 milliliters would be easier and allow for less time for its dissolution than 10 milliliters?

- Is PPM something that can indicate purity? I mean isn't PPM about quantity? The aquarium testing kit refers to PPM and mg/L like it's the same.

- If that test works for 500 milliliters of water are there other parameters that need adjusting?


Thanks

[Edited on 13-8-2023 by carlrodeo]

Cathoderay - 13-8-2023 at 10:45

I don't know where you found that procedure, but it won't work to find the purity of the Na(NO3).
Keep in mind there is only 3.65g of (NO3)- in 5g of Na(NO3), the rest is sodium.
Why mineral water was suggested is very odd, it isn't as pure as distilled water. It prob ably would contain more sodium.

You want to detect 1% or less of impurity in the Sodium Nitrate, that means whatever method you use it has to sensitive enough to do that. How much nitrate is in 1000ml of water isn't the question, those test strips will not help.
Stated in another way, you want to measure how much of 100g is not Na(NO3).
If it was 99% pure then there could be 1g of impurity in 100g of the chemical.
How sensitive is your best scales?


[Edited on 8/14/2023 by Cathoderay]

carlrodeo - 13-8-2023 at 11:23

Quote: Originally posted by Cathoderay  
How sensitive is your best scales?


1000g x0.1g

Rainwater - 13-8-2023 at 16:10

Google precipitation gravimetric. Its under analytical chemistry.

Interesting enough, i remimber reading in one of my books about measuring potassium with the use of sodium hexachloroplatinate.

There where some before steps about removing other cations but specifically for potassium

disolive the hexachloroplatinic acid in water.
Add a slight excess of sodium chloride and dry the resulting solution at 115c.
Extract and recrystallize the newly formed sodium hexachloroplatinate using absolute ethanol(100% dry).
this requires special techniques to prevent water from entering the reaction.

the Na(Pt)salt is soluble in dry ethonol, but the sodium chloride is not.

(A) Weigh a sample of your compound and dissolve it in water
(B) Add a measured excess of the Na(Pt)salt to it.
Dry it again and use pure ethanol to extract the excess Na(Pt)salt
(C) Dry and weigh the extract.

Any potassium cations react in a double displacement reaction with the sodium cations forming
Potassium hexachloroplatinate, which is insoluble in dry ethanol.

Once you have your weights, its simple math.
If you started with 1.0 mol of Na(Pt)salt the recovered 0.5 mol of the salt. You know your sample had 0.5 mols react. If your interested I will try to find the reference about how to remove the other cations that will interfere with this reaction
. Its a thick book. But worth the read. Hope you like calculus.
Oww ya. Platinum salts extremely toxic, Like really toxic. Ant to cheap ether.

Edit:
Or you could heat the sample until molten, wait for the orange gas to go away, then compare the before and after weights. This will tell you the no2 & no3 content

[Edited on 14-8-2023 by Rainwater]

j_sum1 - 14-8-2023 at 03:14

Both sodium ions and nitrate ions are difficult to determine quantitatively using amateur lab gear. Most salts of both ions are soluble which makes any kind of isolation difficult.
I am not aware of any simple indicators for sodium which pretty much rules out any kind of titration.
Nitrate does have oxidising properties and can be determined qualitatively with some indicators. But getting at a result that is meaningful for you -- that is a hard ask. You would need a very selective reaction and a very pronounced end point

For your reported 99% to be inaccurate you are looking at 0.5% deviation from that. That is one part in 200. Most of the time I am happy if my digital scale gives me that. Never mind a titration.

Sulaiman - 14-8-2023 at 05:17

I would probably try a melting point test (308oC)

Looking at a Sigma Aldritch sample COA for >99.5%
https://www.sigmaaldrich.com/certificates/COFA/V8/V800390/V8...
it appears that calcium, potassium and sulphate ions are the most difficult to remove impurities,
but I don't know how to quantitatively test for them.

Cathoderay - 14-8-2023 at 09:49

Quote: Originally posted by carlrodeo  
Quote: Originally posted by Cathoderay  
How sensitive is your best scales?


1000g x0.1g

OK. So if you were to find a way to separate the impurity with complete efficiency from 10g of the chemical then there might be as much as 0.1g. But your scales probably display +-0.1g so you wouldn't have an accurate measurement. Starting with 100g would give you better accuracy, then it could be 1g +-0.1g. That would be a 10% accuracy of how much impurity.
I'll assume that you didn't get the chemical from someplace like Sigma-Aldrich, so the impurity could be anything except NaNO3, even glass powder or fibers, you don't know at this point.
Most probably the impurity is from the method used to manufacture it and also not just one substance. For instance NaNO2, KCl, NaCl, NaSO4, KNO3, etc.
I think you can see from this and the other posts that what you want to find out is not a simple thing. That's one reason reagent grade chemical like those from Sigma-Aldrich are so expensive.

Texium - 14-8-2023 at 09:56

Quote: Originally posted by carlrodeo  
- Is PPM something that can indicate purity? I mean isn't PPM about quantity? The aquarium testing kit refers to PPM and mg/L like it's the same.
It is... for water, since a liter of water is also 1,000,000 mg.

Regardless, it sounds like a crappy method, and you don't even provide the source of where you got it from. Honestly the simplest way to go about this one would be to just run a reaction with it and see if it works the way that it is supposed to. If it doesn't, that's when you can start questioning the purity of your reagents.

Bedlasky - 14-8-2023 at 13:10

Determination of sodium:

1. Gravimetric determination as NaZn(UO2)2(CH3COO)9.6H2O

https://sci-hub.se/https://pubs.acs.org/doi/10.1021/ja01386a...

https://www.jbc.org/article/S0021-9258(18)76500-9/pdf

2. Gravimetric determination as Na[Sb(OH)6].0,5H2O

https://www.jbc.org/article/S0021-9258(18)87225-8/pdf

3. Indirect chelatometric titration of sodium (titration of zinc in sodium zinc uranyl acetate):

https://sci-hub.se/10.1016/0039-9140(79)80099-5

Determination of nitrate:

1. Ferrometric titration in conc. H2SO4 medium

https://sci-hub.se/https://pubs.acs.org/doi/abs/10.1021/ie50...

2. Gravimetric determination as nitron nitrate

https://www.jstage.jst.go.jp/article/analsci1985/6/5/6_5_757...

I personally have only experience with ferrometric determination of nitrates, which works quite well. However visual indication described in document above don't produce good results, it's quite inaccurate. So you need platinum electrode and do potentiometric titration.

I have an idea to remove nitrite produced in this reaction using sulfamic acid and than titrate Fe(III) or excess Fe(II) - this could allow visual indication. But I didn't test this method yet, so I can't say this is reliable method.

B(a)P - 14-8-2023 at 14:26

Your best bet will be to test for potential impurities.
Two good places to start will be the answer to the following questions:
- What impurities will be in your sodium nitrate that will negatively impact the reactions that you propose to use it for? Once you answer this you can devise a test for the problematic impurity. This will be the most important question to answer, because as Cathoderay points out it could be nearly anything depending on your source.
- What impurities are typically in sodium nitrate? A good start would be to work out the percentage of insoluble material, which will be a nice easy test. Carbonate would be another likely contaminant, you could test for this using calcium chloride. You can test for chloride using a soluble mercury or silver salt. A lead salt can be used to test for sulfate. You can deal with cations in a similar fashion, though potassium will be a likely contaminant and tricky to test for.
Bottom line is that it really depends on your proposed use for the product. If the test for purity is more or a curiosity/developing lab skills and knowledge, then walking through the process of testing for individual contaminants might also take your fancy. Testing for a suit of individual contaminants is a good excuse to stock your lab with a few more reagents!:-)

Sulaiman - 14-8-2023 at 22:52

Quote: Originally posted by B(a)P  
If the test for purity is more or a curiosity/developing lab skills and knowledge, then walking through the process of testing for individual contaminants might also take your fancy.
This could be a great adventure and extremely educational and useful,
but analytical chemistry is a giant rabbit hole,
I had a look in, and there seem to be two choices;
. gc/ms, xrf, spectroscopy etc.
. shelves full of (usually hard to get, not cheap and then rarely used) reagents and labware, plus years of 'work', then tedious procedures.

I'm just a poor lazy hobbyist, so neither is suitable for me :(
(notice that SM is very much synthesis biased, very few analysis topics)
but don't let me put you off wet analytical chemistry,
I don't think that you should learn/do chemistry without at least a little analytical chemistry.
Plus, I have negligible experience, so my opinion is ignorable :)

wg48temp9 - 14-8-2023 at 23:46

I will answer your questions.

- Is there a reason why the amount of water has to be 1000ml? Will testing in for example 500ml of water provide not accurate result?

1- Why 5 grams of chemical? Why not 3 grams or 20 grams?

2- Would mixing 5 grams of chemical in 100 millilitres would be easier and allow for less time for its dissolution than 10 millilitres?

3- Is PPM something that can indicate purity? I mean isn't PPM about quantity? The aquarium testing kit refers to PPM and mg/L like it's the same.

4- If that test works for 500 millilitres of water are there other parameters that need adjusting?

Answers:
1)-3g or 20g can be used provided the volume of water is adjusted such that the final concentration is 10 PPM / 10 mg/L. Note: the test strips probably measure the concentration of NO3 so you need to take that into account as you're using NaNO3.

2) Probably.

3)PPM is a concentration, it does not directly indicate purity. PPM is usually the same as mg/l.

4) As in answer 1, 500ml can be used provided the mass of NO3 is adjusted such the final concentration is 10 PPM / 10mg/l. Note: If your volume measuring device is a 1l volumetric flask, then using 1l would be convenient.

Note: Aquarium test strips are designed to operate in the presence of impurities in aquarium water and cannot distinguish between sodium nitrate, potassium nitrate or nitric acid. The resolution of the colour comparison by eye with the colour chart is probably only 1 in 10 not sufficient to distinguish between 99 and 98 for example. Then there is the accuracy of measuring the mass of the nitrate to only 0.1g. Using aquarium test strips will not give you a meaningful answer to the question is your NaNO3 99% pure.

carlrodeo - 15-8-2023 at 00:53

Quote:
Answers:
1)-3g or 20g can be used provided the volume of water is adjusted such that the final concentration is 10 PPM / 10 mg/L. Note: the test strips probably measure the concentration of NO3 so you need to take that into account as you're using NaNO3.

4) As in answer 1, 500ml can be used provided the mass of NO3 is adjusted such the final concentration is 10 PPM / 10mg/l. Note: If your volume measuring device is a 1l volumetric flask, then using 1l would be convenient.


@wg48temp9 How do I adjust the proportions of chemical's mass and water properly to not overdo it and not underdo it?

RU_KLO - 15-8-2023 at 10:44

As stated before, maybe you could indirectly meassure (find) purity, by precipitating any impurity.

In "classical qualitative chemistry" H2S scheme - Sodium cation is one of the last (6th group) so any indication before, you will get your impurity.
Note that this is qualitative, not quantitative. It will show that you have an impurity, not the amount.
This will find usefull for K+, Na+ cations, because their are last in the scheme, other cations are in previous groups (Fe+ for example is in group 3), so impurities from further groups (4+) will not be detected.

Once you know wich impurity you have, you could do a quantitative test.

Also note that this shows different cation impurity, if your impurity has the same cation, this will not work. (example Sodium chloride or sodium carbonate impurity)

wg48temp9 - 15-8-2023 at 11:26

Quote: Originally posted by carlrodeo  


snip

@wg48temp9 How do I adjust the proportions of chemical's mass and water properly to not overdo it and not under do it?


You suggested a concentration of 10 PPM / 10mg/L. Ideally this concentration would be the mid-point of the range of your test strip

A concentration is a ratio between the solute (NO3) and the solvent (water), expressed (in this case) as the mass in mg of (NO3) divided by the volume of the solvent in ml. (you may need to swot up on fractions and proportional problems)

It complicated in your procedure as it contains an initial dilution to allow the use of grams of the solute rather mg. Instruction 1,2 and 3 produce a concentration of 5g/1000ml (5mg/ml).
It then takes 2ml of that solution (5g/1000ml) and adds it to 1000ml of solvent. Each ml of the 5g/1000ml solution contains 5mg (5/1000= 0.005 = 5mg),so 2ml contains 10mg solute which is added to 1000mg to produce a concentration of 10mg/1000ml or 10 PPM (0.01/1000= 10/1000,000)

In the first dilution procedure 10g of solute could be added to 2l or 2.5g could be added to 500ml, both produce a concentration of 5mg/ml.

Similarly, in the last dilution 1ml of the 5mg/ml solution to 500ml or 10ml could be added to 5,000ml.

Note: strictly for accuracy, you add the solute to less the the required volume and make the solution volume up to the required volume. You should also do the same with final dilution.

Hopefully the above is explanatory for you.


B(a)P - 15-8-2023 at 12:42

As wg48temp9 has stated, the accuracy that you are trying to achieve, less than 1%, is not possible with the standard aquarium tests strips. Even with the best test strips available you may not be able to achieve what you are trying to do. At the dilution you have described your test strip will need a resolution better than 100 ppb. When you account for the error in the measurements that you need to make the resolution will need to be lower. You will need to be able measure the difference between 10.00 ppm and 10.05 ppm, at least. The aquarium test strips that I am familiar with will be in increments of 0,10,25,50 ppm or similar.

Bedlasky - 16-8-2023 at 08:06

Quote: Originally posted by Sulaiman  
This could be a great adventure and extremely educational and useful,
but analytical chemistry is a giant rabbit hole,
I had a look in, and there seem to be two choices;
. gc/ms, xrf, spectroscopy etc.
. shelves full of (usually hard to get, not cheap and then rarely used) reagents and labware, plus years of 'work', then tedious procedures.


That's not true, analytical chemistry is well available for hobby chemists. You don't need expensive machines or exotic reagents at all. For qualitative analysis you need just common reagents, for quantitative analysis some extra glassware and good scales (you usually don't need expensive analytical scales for home chemistry purposes). Analysis of inorganic substances is pretty simple, organic substances are more difficult if you need to find exact formula of the substance, but functional group analysis isn't usually hard.

[Edited on 16-8-2023 by Bedlasky]

Cathoderay - 16-8-2023 at 09:47

Carlrodeo, it somewhat depends on how badly you want to know about the purity.

I'm interested in metal analysis so I am familiar with some inorganic qualitative analysis.
Qualitative analysis asks what is there and Quantitative analysis asks how much is there.

Complete inorganic analysis does require many reagents to check for all the possibilities but you could skip some because they would be so unlikely. For instance it is unlikely that there is much silver, cobalt, chromium or mercury as an impurity in the NaNO3.
Analysis does not require a large amount of any one reagent however. You would be using drops or a few milliliter of those solutions.
You would need a number of test tubes and a centrifuge, etc.

I remember doing some qualitative analysis in high school, I wish I still had the lab manual.
The best videos I have found online is this series by Tyler Johns. You have to overlook his need to talk loudly. It seems he did most of these as an addition to chemistry classes.
https://www.youtube.com/channel/UCHUQV61jHGEl9ntRR6sQdHw/vid...