I have a bottle of salt water I collected on a local beach. I want to see what is in it, apart from water and salt. If I boil the whole bottle and wait for it to evaporate, mostly salt will remain. I want to see everything except salt that is still in the pot after I boil the water. Is this possible with common household items and commonly available (and safe) chemicals?

Disclaimer: I know nothing about chemistry.

  • $\begingroup$ How do you know there is anything other than water and salt in the first place? $\endgroup$ – Ivan Neretin Aug 21 '17 at 5:50
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    $\begingroup$ The water is often pretty dirty, supposedly because criminal organizations dump waste at night. I'm curious to see if there is anything visible to the naked eye after evaporating a bunch of jugs filled with water. $\endgroup$ – user51012 Aug 21 '17 at 6:07
  • $\begingroup$ Is there anything visible now, before any evaporating? $\endgroup$ – Ivan Neretin Aug 21 '17 at 6:25
  • $\begingroup$ I'm getting ready to go to the beach right now! I'll report later. $\endgroup$ – user51012 Aug 21 '17 at 6:29
  • $\begingroup$ Sea water contains lots of salts not just sodium chloride. Are you interested in the others? or do you just want to remove the sodium chloride? And you are equating whether household items can replicate what analytical chemical labs with lots of dedicated equipment: that could be a stretch. $\endgroup$ – matt_black Aug 21 '17 at 8:42

You could remove the bulk of the sodium chloride (and most other salts) by evaporation and crystallization. Most of the impurities you are looking for are going to stay in solution or suspension when you filter off the salts.

You could also use dialysis to remove the remaining salts: this requires a bag or length of thin-walled tubing made of a common polymer such as cellulose acetate. Tie off one end (the bottom), put the concentrate from the above step into the tubing, and tie off the top end. Then place it in a bucket of distilled water. The salts and other small molecules will diffuse out into the water, whereas the higher molecular weight materials like toxins will stay in the bag. You may need to change the water in the bucket a few times to get rid of all the salts.

You will still need some chemistry to figure out what substances remain in the bag. With seawater, it could be a very complex mix. However, looking at it with a fluorescent light might show something interesting. Good luck, and hope you get inspired to study chemistry!

  • $\begingroup$ Exactly what I wanted! :) I am inspired to study chemistry already, but right now I have a bit too much on my plate, especially with music software programming (I'm making my own DAW with most of my free time). Chemistry is one of the first things I want to learn when I have more time. $\endgroup$ – user51012 Aug 21 '17 at 19:06

You could use ion exchange resin to remove the salt, I would use DOWEX-50 in the protonated form. I would wash it several times with water to remove the yellow water soluble impurity which is normally on brand new DOWEX-50- I would mix it with the water at the same time. I would then add to the water IRA-67 (weak base resin) in the free base form. I would have washed it first. This combination will remove the sodium chloride from water.

However if I wanted to see what was in the water, then this desalination treatment with resin would be counterproductive.

If I wanted to find out what organics were in the water, then I would extract with diethyl ether or ethyl acetate. The sodium chloride in the water will reduce the amount of the organic solvent which dissolves in the water. It will also sometimes increase the partioning of the organic solute into the organic phase. I would be then wanting to inject the organic extraxct into a gas chromatography machine after dilution with hexane and drying with sodium sulfate.

If I was to want to isolate metals from the water, then I would be looking to do solvent extraction. Depending on the metal I am interested in I would either use 30 % DEHPA in kerosene or 30 % aliquat 336 in toluene.

The DEHPA (Di- 2-ethylhexyl hydrogen phosphate) will extract many divalent metals from the water, depending on the pH it can extract calcium, strontium, barium and lanthanides. I would strip the metals using nitric acid.

The aliquat 336 is able to extract from sodium chloride solution things like copper, zinc, cadmium, iron and cobalt. I would want to strip (back extract) the metals from the aliquat phase into dilute nitric acid, then I would want to use ICPOES or AAS to measure them.

The general idea is that if you take a clean glass bottle and put in it 200 ml of the water sample, 20 ml of the organic phase. You then seal it and shake it. Then take a 15 ml sample of the organic phase to a smaller vial and add 5 ml of the strip solution. This has the potential to increase the concentration of the metals.

The problem is that if I was to use the DOWEX-50 resin on the orginal water sample then it would remove many of the metals which we want to measure using the solvent extraction pretreatment method.

In general if you want to measure things in salt water, I would try to devise methods of recovering the anaylte without needing to remove the common salt.


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