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Old 01-22-2013, 04:14 PM   #11
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That's partly why I said I shouldn't be but, reverting to a former life as an electrical engineer I'll note that it's 'only' a 1.65 dB shift.

I went to a lot of trouble in my spreadsheet to pay attention to temperature. It reflects the dependence on temperature not only of pKw but also the pKa's and pKs's for any acid we use wherever I could find data. There was a reason I took that trouble but I guess we forget as time passes.

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Old 01-22-2013, 04:30 PM   #12
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This brings up the question of temperature and how it affects things. If we assume that all mash pH and water chemistry discussion centers around pH measurements at standard temperature (25 C) we should always be using a pKw of 14. Is this correct?

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Old 01-22-2013, 06:45 PM   #13
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The polynomial I have, pKw = 4471/K -6.0875 +0.01706*K says that it hits 14 at K = 279.99 (24.8 °C). That's a bit warm for lab/room temperature (76.7 °F). My concept of room temperature is more like 20 °C and I believe that ASHRAE's defintition. I have noticed, however, that when you check into a hotel room anywhere else in the world the thermostat seems most likely to be set for 21 °C.

I have always used 20 °C unless I have special reason not to and that is probably because the ASBC Plato table is for 20°C/20°C specific gravities. Plus the pK values one typically sees for carbonic acid match 20°C (but are very little different for 25°C).

If you look up sucrose on Wikipedia it gives the solubilty at 25 °C but ICUMSA defines the standard sucrose soultion at 20 °C and all its formulae (for density and refractive index) are Taylor series expansions around 20 °C. OIML's ethanol formula is also expanded around 20 °C. Anton Paar's densitometers ship set for 20 °C. etc. If you look in the CRC Handbook you'll find lots of SG data referenced to 25°C and lots to 20°C and some to lower temperatures. Glacial acetic acid is called glacial because in the days it was named laboratory temperature was closer to 17 °C than 20 (I guess scientists were more rugged then). Also, referring again to electrical engineering, noise figure calculations are referenced to 290 K (17°C) supporting the idea that lab temperature was 17 °C years back.

My impression of all this is that in the middle of the 20th century 25°C became the 'standard' temperature but that more recently it has fallen back to 20 as almost everything coming out these days seems to be based on that number.

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Old 01-22-2013, 10:35 PM   #14
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Thanks for this detailed response. I also find 25 C a bit warm for room temp. But I'm using it as the standard temp for my pH measurements. The mighbe a few cases where the 5 C difference matters, but for the most part we should be fine.

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Old 01-25-2013, 06:49 PM   #15
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Well, I just bottled my first batch where I actually KNEW what the pH level was. I did Orfy's mild recipe and came in right around 5.4 without any modifications. That however puts my calcium level just a little low. I'll try some calcium chloride and a little lime next time around. I don't want to drive the pH lower so I figure I'll need a little lime. Hydrometer sample seemed to have nothing unpleasant about it.

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Old 02-01-2013, 07:55 PM   #16
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Quote:
Originally Posted by Kaiser View Post
the pH of tap water should not be that high. I think 9.5 is the highest that the EPA allows.

And yes, the drop kits have an inherent error which is particularly noticeable when you need only a few drops. You could increase the precision by taking twice the sample volume and dividing the drop count by two. But that doesn't get rid of the systematic error caused by drop sizes that are not the same size as intended by the manufacturer.


Kai
I never did get an answer from the city but I did finally track this down. It is from 2011 and is just labeled "typical". Since it is reservoir water I know it changes.

This is ugly going from postscript to spreadsheet to web page but I'm not going to obsess to much.
Code:
The following analysis is typical of the treated water from our plant
PH			10.69	
Turbidity			0.11	NTU 
Alkalinity-Total		43	mg/I as CaCO3 
Alkalinity-Phenolphthalein	31	mg/l as CaCO3 
Alkalinity-Hydroxide		19	mg/l as CaCO3 
Alkalinity-Carbonate		24	mg/l as CaCO3 
Alkalinity-Calcium Carbonate Stability			11	
Hardness-Total			94	mg/l as CaCO3 
Hardness-Non carbonate	         51	mg/l as CaCO3 
Chlorine Residual-Total		1.8	mg/I 
Chlorine Residual-Free		0	mg/I 
SOlids-Total			254	mg/I 
Conductivity 			521	umhos/cm 
Threshold Odor Number 			1
Just put this here to answer the high pH question. Yeah, it is real. These numbers (not all shown here) put into your new online calculator got me to about .03 pH reading though. But, that is another story for the other thread.
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