Sciencemadness Discussion Board - Why does my Distilled water have a pH of 5.6 ???

Why does my Distilled water have a pH of 5.6 ???

mayfieldtm - 13-3-2012 at 17:24

I just received a Pocket PIN PH Meter that I purchased on Ebay, Model PH-009.
It came with 2 calibration solutions, ph 4.0 and ph 6.7.
I calibrated it per instructions, and it needed only slight adjustment.
Seems to work great!
However when I check the pH of my Distilled Water that I just purchased at my local Supermarket, I got a reading of pH 5.6!
What do you think? Is my water that Acid or my PH Meter junk or am I expecting too much?
By the way. I mixed the calibration solutions with the same water.
Tom M.

bfesser - 13-3-2012 at 17:40

Dissolved CO2 as <a href="http://en.wikipedia.org/wiki/Carbonic_acid#pH_and_composition_of_carbonic_acid_solutions" target="_blank">H2CO3(aq)</a> <img src="../scipics/_wiki.png" />? Note that your value of 5.6 is equal to the highlighted table value of 5.62 (less 1 <a href="http://en.wikipedia.org/wiki/Significant_figures" target="_blank">S.F.</a> <img src="../scipics/_wiki.png" />

. Don't worry, there is nothing wrong with your pH meter or distilled water. If you have litmus or other pH strips, compare to those.

Quote:

• For vanishing pCO2, the pH is close to the one of pure water (pH = 7) and the dissolved carbon is essentially in the HCO3− form.
• For normal atmospheric conditions ( atm), we get a slightly acid solution (pH = 5.7) and the dissolved carbon is now essentially in the CO2 form. From this pressure on, [OH−] becomes also negligible so that the ionized part of the solution is now an equimolar mixture of H+ and HCO3−.

Pure water, with no gases dissolved into it, will have a pH of 7. Since your water has absorbed CO2 from the atmosphere, forming carbonic acid, your meter will read a pH of ~5.6. This is normal and essentially unavoidable. Try the following experiment: boil a sample of the water, cover & let cool enough to take it's pH, and report back to us with the value.

[aside] Could a mod please move this to Beginnings?

[Edited on 7/9/13 by bfesser]

Arsole - 13-3-2012 at 18:25

Good to know I would not have thought about that.

peach - 13-3-2012 at 19:01

Filtering tap water (mine is 6.5) through ion exchange resins also causes an immediate drop in it's pH to 5.7.

This is also the cheapest and easiest way to produce what could be termed purified water. So another possibility is that it's come from such a filter, rather than been distilled.

A number of places have been told off for selling what is simply filtered tap water as something exotic.

Cola's Dansani being a big name example; although they went for reverse osmosis.

Quote:

It goes something like this: take Thames Water from the tap in your factory in Sidcup, Kent; put it through a purification process, call it "pure" and give it a mark-up from 0.03p to 95p per half litre***; in the process, add a batch of calcium chloride, containing bromide, for "taste profile"; then pump ozone through it, oxidising the bromide - which is not a problem - into bromate - which is. Finally, dispatch to the shops bottles of water containing up to twice the legal limit for bromate (10 micrograms per litre).

- "Things get worse with Coke", the Gaurdian

***That's >3000x the price of tap water.

Quote:

Early advertisements referred to Dasani as "bottled spunk" or featured the tagline "can't live without spunk". These slogans were used seemingly oblivious to the fact that spunk is slang for semen in the UK.

[Edited on 14-3-2012 by peach]

Vikascoder - 14-3-2012 at 00:39

the water you buyed is not actuall pure there are some ions in it which reduces its ph

Endimion17 - 14-3-2012 at 06:06

"Distilled water" might not be distilled at all. Usually there's a fine print saying something like "made using ion exchange". Sometimes, you get ripped off because there is no such info at all.
I buy one brand for which I know for sure that only distilled water is used.

gutter_ca - 14-3-2012 at 07:52

If you heat the water slightly to off gas CO2 your water will be closer to pH 7.

mayfieldtm - 14-3-2012 at 09:54

Thanks all for the responses!

I boiled the water and now get a reading of pH 6.3.
Closer to pH 7.0.

So, now I'm on a quest for a source of better water.
I think soon I'll set up a distiller.

Tom M.

gutter_ca - 14-3-2012 at 11:11

All DI water will readily absorb atmospheric CO2, dropping the pH on exposure to air.

bfesser - 14-3-2012 at 11:33

Quote: Originally posted by mayfieldtm

Thanks all for the responses!

I boiled the water and now get a reading of pH 6.3.
Closer to pH 7.0.

So, now I'm on a quest for a source of better water.
I think soon I'll set up a distiller.

Tom M.

Don't listen to them. It may actually be distilled water. To test it, boil some down to concentrate any ions present. Prepare a little AgNO3(aq.) solution from the unconcentrated water. Add a few drops to a sample of the concentrated water. If a precipitate appears, then you have significant Cl-, I-, Br-, S2-, or other contaminant ions. If no precipitate appears, it's good enough for just about any experimentation you'll do in a home lab.

<hr width="300" />

Quote: Originally posted by gutter_ca

All DI water will readily absorb atmospheric CO2, dropping the pH on exposure to air.

gutter_ca, do you even bother to read a thread before posting? I already explained this (in the second post in this thread!). And, I already told him to do this:

Quote:

If you heat the water slightly to off gas CO2 your water will be closer to pH 7.

[edit: fixed markup typo]

[Edited on 7/6/13 by bfesser]

gutter_ca - 14-3-2012 at 11:52

Obviously, the OP didn't get it. He thinks he needs a "better" water source.

iExplore - 14-3-2012 at 15:11

Quote: Originally posted by peach

[url=http://www.sciencemadness.org/talk/viewthread.php?tid=18221#pid229657]

Cola's Dansani being a big name example; although they went for reverse osmosis.

Quote:

It goes something like this: take Thames Water from the tap in your factory in Sidcup, Kent...

- "Things get worse with Coke", the Gaurdian

***That's >3000x the price of tap water.

In all fairness, if you consider how many kidneys that water has passed through, it's probably some of the purest in the country...

mayfieldtm - 14-3-2012 at 20:30

bfesser wrote...

>>>>>

Don't listen to them. It may actually be distilled water. To test it, boil some down to concentrate any ions present.
Prepare a little AgNO3(aq.) solution from the unconcentrated water. Add a few drops to a sample of the concentrated
water. If a precipitate appears, then you have significant Cl-, I-, Br-, S2-, or other contaminant ions. If no precipitate
appears, it's good enough for just about any experimentation you'll do in a home lab.

>>>>>

Thanks bfesser:
I will do your experiment.
I need to order some Silver Nitrate.

By the Way... the water Lable reads...
"Purified by Steam, Filtered and Ozonated".

Tom M

Tom M.

[Edited on 15-3-2012 by mayfieldtm]