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wait a minute...what's the ph of distilled water

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extrememetal43

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Isn't distilled water supposed to have a pH of 7. A buddy of mine got a new pH tester today and was testing the pH of various things. It came with a buffer solution to 7.01 and he calibrated it accordingly. He tested the pH of 5% white distilled vinegar and it came in at around 2.5 which is pretty accurate.

Then he tested the pH of distilled water and it came in at 5.8. He was like wtf isnt it supposed to be 7. He thought pure water was pH of 7. He tested the tap water it came in around 7.2, then he tested some spring water out of a bottle and it came in at 7.1, He was really confused so he looked it up and some places say it's supposed to be 7 or SLIGHTLY under and other's it said it can be significantly lower due to absorbing CO2 from the atmosphere.

So which is it? and how does this affect extractions...they all call 4 distilled? Should i be concerned of the low pH of it at 5.8?
 
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ya he didn't have the ph 4 buffer solution...he assumed since the ph 7 came out right and the vinegar test was pretty close +/- .1 that it would be relatively close, ph within a few points is fine by him.

while on the subject of ph testers how important is calibration and using the storage solutions?
 
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The doubly distilled water we have in the lab (molecular biology grade) comes out of the machine with a pH of 7. As long as you leave it at room temperature the pH will start falling. Within some time it will get at around 4 and it will be stabilised around this value.

I was very baffled with this phenomenon in the beginning and I couldn't believe the reading of the pH meter. After some searching on the internet I discovered that the most likely source is the dissolving of atmospheric CO2 into the water, as benzyme noted.

and that makes sense, since CO2 + H2O <-> H2CO3, then H2CO3 <-> CO3- + 2H+ (the latter lowiring your pH)

hope that makes sense!
 
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the distilled contains less extra junk still, salts, minerals, etc. so technically it will be easier to grab the deems

carbonic acid is pretty weak and should be overpowered by the common extraction acids and bases
 
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Yeah, the water pH is always going to drop because of CO2 dissolving in it from the air.

This can also happen with some alkaloids. For example freebase mescaline is well known for combining with the CO2 in the air to form mescaline carbonate. Mescaline has a pKa of 9.56. Just leaving it out in the open air for a while will form mescaline carbonate. It will even form in an air tight jar if there was enough CO2 in the jar when the jar was closed. This isn’t a problem though, because you normally don’t vaporize mescaline.

Bufotenine has a pKa of 9.67, higher than that of mescaline, which explains why it also forms bufotenine carbonate when left in the open air. I've heard that bufotenine also oxidizes after this, so you eventually end up with bufotenine N-oxide carbonate, which is said to be slightly hygroscopic sticky black material. Is this true? SWIM has seen old pure amber freebase bufotenine turn nearly black and sort of sticky after prolonged storage without proper protection of air.

It’s really not necessary to use distilled water. You can use the purified drinking water sold at supermarkets that states on the container that it’s a substitute for distilled water. It’s much cheaper than distilled water and nearly the same quality. I tested it myself and the level of contaminants is extremely low, like 0.1 - 0.5 ppm (0.1 - 0.5 mg per liter!) or less. To give you an idea of how pure that is, spring water is usually 50-300 ppm, mineral water is usually 250 ppm or more.

So imagine, if you used simply good quality purified water with only 0.5 mg per liter of contaminants, and you did a typical extraction with say 3 liters of water, at the most your product could be contaminated with maybe 1.5 mg of compounds. That’s it. Most of these would be minerals that are insoluble in non-polar solvents, so it’s more likely that next to nothing from the original water will end up in your end product using an A/B extraction.
 
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damn how many kinds of water are there...distilled, spring, tap, and now purified drinkin water. No big deal just kinda came as a surprise to me i thot its ph would have been 7. It is good to kno for future reference.
 
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what's a buffer? r u saying if there's a slight amount of anything in there it would stay constant.

also, a question about real chemistry profesional lab use, would u use only distilled water at ph7 outa the machine so to say in very complex or certain prosesses? or is it somethin that dont really matter?
 
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I guess thats another reason why it'd be cool to just use 'pure' water in a soxhlet or for extracting spice, because over 90% should be ionized at a pH of 6.68 wasn't it?

EDIT: did your friend rise the pH tester properly after testing the vinegar?
 
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it was rinsed. Ya but in seein that the ph was 5.8 i'm thinkin that there's like absolutely pretty much no acid in at that ph. I mean if something's ph 5.8 i'm thinkin it's just a very lil acid. If u think of the numerics of that scale it's very cool. Cuz very small discrepensies can be catered w differences at small amounts and large amounts could be distinguished at high amounts.
 
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what's a buffer? r u saying if there's a slight amount of anything in there it would stay constant.
Click to expand...
a buffer is typically an acetate/phosphate salt dissolved in DI water. the pH lies between two known dissociation constants of a solute in solution

also, a question about real chemistry profesional lab use, would u use only distilled water at ph7 outa the machine so to say in very complex or certain prosesses? or is it somethin that dont really matter?
Click to expand...

one word: purity.

science is about reproducibility.
 
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benzyme said:
what's a buffer? r u saying if there's a slight amount of anything in there it would stay constant.
Click to expand...
a buffer is typically an acetate/phosphate salt dissolved in DI water. the pH lies between two known dissociation constants of a solute in solution

also, a question about real chemistry profesional lab use, would u use only distilled water at ph7 outa the machine so to say in very complex or certain prosesses? or is it somethin that dont really matter?
Click to expand...

one word: purity.

science is about reproducibility.
Click to expand...

i dont understand a word of that...r u sayin when doin an experiment u gota repeat it so if u use water at ph 5.8 one time u gota use the same the next to be able to do it. Ok and those dissociation constant is that pKa...For example would the pKa of water be 7 and it can flucuate either way a bit and when speaking of spice is that that 8.68 and it can fluctuate within a couple points either way?
 
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Also if you are doing any form of analytical chemistry the impurities in tap or even MilliQ water can show up in instruments.
Thus most use HPLC or MS grade water, but that is really high purity and very expensive.

For plant extractions 69-cent distilled from Wal-Mart should be more than good enough.
 
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You often can't get a accurate PH reading on distilled water.., there's a reason for that relating to it's lack of any disolved solids.. to calibrate my PH pen I just stick it under the tap, and compare the reading with the water quality report available on the internet from my local municipality.
 
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