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Distilled water! (again)

Posted: 19 Oct 2006, 10:02
by Ian
Hi all.
I am new to this Website this week, but was interested to read the forum on Distilled Water. This is relevant to me at the moment as our distillation machine seems to be malfunctioning and only produces about 2L per day, but uses about 12-15L per minute for cooling! (Ouch!)

I have found that the local IGA store sells both Distilled water, and Denmineralised water, both for about $1.45 per 2L bottle. (good! Mitre 10 wanted to charge me $3.10 for iL!!)

I have tested both for conductivity with the Streamwatch conductivity probe thingie and got 0 uS for each. (compared to 170 uS for Warragamba tap water) Both give a crystal clear solution when I add AgNO3 (compared do white soup with tap water) but when I tested for pH using the "Precision" pH testing strips, with the four coloured squares to compare, the Distilled water registered as pH 5.5, and the Demineralised came up as pH 5 (compared to Sydney tap water which was spot on pH 7!!)

Can anybody tell me why Distilled water would have a pH of 5.5 instead of 7 and more importantly, does it really matter? (My Chem teacher is planning on doing titrations this term with his senior classes and I want everything to be right.)

Regards
Ian

Posted: 19 Oct 2006, 10:36
by kate1
I've been told that distilled water is slightly acidic because it absorbs carbon dioxide from the air. Our distilled water has a low pH too.

Distilled Water - High pH

Posted: 19 Oct 2006, 10:40
by Robb
Hi Ian,

The thing we have to remember with distilled water is that there are no ions in it as pure H2O.

Having said that because of this there is always absorbtion of Carbon Dioxide from the atmosphere which then dissolves in the Dist. Water to give slight concentrations of Carbonic Acid. This explains the reason behind the slight High pH 5 - 5.5. This is quite normal..

Hope this has stopped any confusion.

Cheers,

Robb....

Posted: 19 Oct 2006, 11:24
by KimFenley
Hi you can adjust the pH with a buffered base solution if you really want ph 7

Kim

Distilled Water

Posted: 19 Oct 2006, 12:29
by Robb
Hi KimFenley,

pH ranges between 5-7.5 maybe 8 will be normal in lost cases. if you are making up accurate solutions make sure there is nothing added to your Distilled Water stock, otherwise this may have an effect of final concentrations.

Just something to keep in mind!

Cheers,

Robb...........

distilled water

Posted: 19 Oct 2006, 14:53
by rp
Hi Ian
I make mine up fresh from my instant deioniser that is attached permanently to the tap (vertex) and I get ph 7 and it does 2 litres in a few minutes.Its great but a little pricey .
Its well worth buying it if you have the money
Rhonda

Re: distilled water

Posted: 10 Feb 2009, 11:44
by nickykinz
I am at a school where we have no still or deioniser. I will need to buy some water but which do I need to buy? Will deionised do everything or will I still need distilled for some things? I bought some demineralised from Bunnings yesterday just to see me through but I think that it was fairly expensive and is the same as deionised.
Nicky

Re: distilled water

Posted: 10 Feb 2009, 12:33
by Robdean
I'm also using demineralised water from Woolworths - just for making solutions such as silver nirate and for senior chem pracs calling for distilled water. Our chem teacher is more than happy with the results. Our last water still was past its use by date and unfixable so for us this is a cost effective solution. I hated seeing all that water pour down the sink when using our dreadfully slow still!

Re: distilled water

Posted: 10 Feb 2009, 13:25
by Sassi
We have a very old still, which wastes a lot of water! First thing I did when I started here was to purchase a proper still. We still have the old one laying about. I shall ask my HOD and perhaps she will agree to donate it to your school... Leav it with me!

Sassi

Re: distilled water

Posted: 11 Feb 2009, 07:00
by sharonm
I've been getting our demineralised water from Big W 4Lt for around $3. They are generally pretty well stocked areound here.

Re: distilled water

Posted: 17 Feb 2009, 23:39
by smiley
I'm sure I said this somewhere last year, but check out your local car battery suppliers. I but demineralised water for 50c per litre, which is the cheapest in town, from our local battery bloke. Way more economical than Bunnings or Big W.

Re: distilled water

Posted: 18 Feb 2009, 10:27
by MariaC
:D Im very glad this subject has come up cos Im just about to order 40 L of distilled water at a cost of ninety dollars because our distilled water (previously bought) has a pH of 5.5. The chem teacher doesnt want me to use it to make up senior chemicals, is it really a problem???? Also I bought pH buffer tablets to make up some buffers to calibrate our pH probe with, will using distilled water with a pH of 5.5 affect the accuracy of the buffer or will the buffer "buffer" itself!!! :-( :? :oops: Thanks heaps for any imput, I love this site :wub: :wub: Maria

Re: distilled water

Posted: 18 Feb 2009, 10:41
by sunray18
I now get my Distilled water from 'Water to Go' delivered to my prep room for $20 for 4L... works well for me..

Re: distilled water

Posted: 18 Feb 2009, 10:50
by RosalieM
You can get 4L for less than $4 at Big W. $20 is a lot, even delivered! Is Booragul big enough for a Big W? You'd save your science department a lot of money! During the drought I got mine from Blackwoods $20 for 20L but now the dam is full (yay!!) I am back to using the still. Although at the rate the 'waste' water comes out compared to the amount of distilled water we get, the dam may not be full much longer!

Re: distilled water

Posted: 18 Feb 2009, 11:47
by Labbie
Please remember the forum rules, do not name companies.

Thanks

Re: distilled water

Posted: 24 Feb 2009, 09:10
by cheltie
Hi everyone,
We used to have a still but have changed over to a deioniser.
The distilled water would sometimes have a PH of 6 but the deionised water I have just used has a PH of nearly 8. Is this normal? The teachers are a little confused by the readings.
Helen

Re: distilled water

Posted: 24 Feb 2009, 09:37
by rosiegbh
Hi, I also have a question on distilled water.
Is there an expiry date on distilled water? I make it through a still and I am now thinking I should put date on the spray bottles I make up. Is this correct? Does it deteriorate over time like the chemical solutions?

Rosemary :?

Re: distilled water

Posted: 24 Feb 2009, 10:15
by Labbie
good question, should take bets on the answer. :w00t:

Re: distilled water

Posted: 25 Feb 2009, 08:11
by Ian
rosiegbh wrote:Hi, I also have a question on distilled water.
Is there an expiry date on distilled water? I make it through a still and I am now thinking I should put date on the spray bottles I make up. Is this correct? Does it deteriorate over time like the chemical solutions?

Rosemary :?
Surely it would depend on how sterile is the container. Biological contamination would be the only problem. The water itself should last several millennia! :-)

Ian

Re: Distilled Water

Posted: 28 Feb 2009, 21:21
by Robb
MariaC wrote::D Im very glad this subject has come up cos Im just about to order 40 L of distilled water at a cost of ninety dollars because our distilled water (previously bought) has a pH of 5.5. The chem teacher doesnt want me to use it to make up senior chemicals, is it really a problem???? Also I bought pH buffer tablets to make up some buffers to calibrate our pH probe with, will using distilled water with a pH of 5.5 affect the accuracy of the buffer or will the buffer "buffer" itself!!! :-( :? :oops: Thanks heaps for any imput, I love this site :wub: :wub: Maria

Hi MariaC,

In the case here, We need to take into consideration pure chemistry here, pH will fluctuate according to town water sources and the amount of CO2 absorbance from the atmosphere, regardless its going to happen, in some cases CO2 absorbance will balance out pH but most cases this does not happen.

Deionised water acts as a CO2grabber, it see's it in the air and pulls it in, like a hungry crocodile...

I have measured Modulab water which is "Pure Water" in my research days and the change in pH is within minutes. Modulab is H2O nothing else, measuring its resistance and conductivity at the same time is the only indication of its pure water state. Never open a bottle for longer than necesarry with this type of water.

In schools you will never come into contact with it, its just too expensive for the instrumentation and also cost to buy.

As far as buffers go for buffering or calibrating pH probes, only use the tablets if you have a pH probe that can be calibrated either by software or the desk top calibration and Onscreen disply. The tablet will not affect the normal workings of the probe even when the water is at pH 5 - 5.5, naturally enough the water will not be an issue for titrations. Also good argument to use is that pH is also very temperature dependant. This could also be a major contributor.

I hope this brings a good conclusion to your questions..

Cheers,

Robb.....