# experience with pH meter?



## Wayne1 (Nov 26, 2008)

Hello all - I just tried measuring acid with the sodium hydroxide - phenolphthalein method of judging color changes for the first time and couldn't make heads or tails of it! I'm wondering whetherthe pH meter is really as simple as it appears or if I need to work more on the judging-color method- 


http://www.finevinewines.com/ProdDetA.asp?PartNumber=5436


I'm wondering what experience people have had with the meter?


Thanks for any input!!
Wayne


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## grapeman (Nov 26, 2008)

It REALLY is that simple! Just add the hydroxide until you get to 8.2 and you have reached the change point. Make any needed calculations for the test and you are done. SIMPLE


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## Jwhelan939 (Nov 26, 2008)

As appleman said, its perfect!!!


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## gaudet (Nov 27, 2008)

SO basically you would take your regular 15 ml sample, add the indicator then add the NaOH in 1/2 ml increments, stir and check the pH. Repeat until you reach pH of 8.2 then do the calculations with the amount of NaOH used to reach endpoint.


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## grapeman (Nov 27, 2008)

I just str with the checker and get a constant reading that way. It changes very fast. Add more slowly as you get close because it will change from about 7.9 to 8.2 or more in a flash. If you go by the trigger point just subtract the last increment you added.


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## Jwhelan939 (Nov 27, 2008)

dido on appleman. It can be somewhat tricky to get the 8.2. After a few practice shots youll be a pro!


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## Wayne1 (Dec 1, 2008)

Thanks for all the comments - I'm going to ask Santa for this!
Wayne


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## grapeman (Dec 1, 2008)

Hey Waldo, Wayne wants you to give him a pH Checker for Christmas.


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## gaudet (Dec 1, 2008)

I'll take one too Santa....

I've been a good boy most of the year......

*Edited by: gaudet *


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## Jwhelan939 (Dec 1, 2008)

Hey, while your giving gifts, I could use a couple dozen bottles!


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## gaudet (Dec 1, 2008)

Jwhelan939 said:


> Hey, while your giving gifts, I could use a couple dozen bottles!



Empty or full????


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## Jwhelan939 (Dec 1, 2008)

Lol, I'm not particular!!!


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## suprasteve (Dec 1, 2008)

gaudet said:


> SO basically you would take your regular 15 ml sample, add the indicator then add the NaOH in 1/2 ml increments, stir and check the pH. Repeat until you reach pH of 8.2 then do the calculations with the amount of NaOH used to reach endpoint.


I don't believe adding the indicator is necessary anymore, but I'm sure it couldn't hurt either, just trying to save you a couple cents at a time!


But this brings up a question of my own, a pH of 8.2 is close to 7 in the big scheme of pH's, but to be EXACT, shouldn't we only add NaOH until we hit 7, or is that factored into the equation for the titration? Cause when you hit 7 that's when the acid/base reaction is 'even', don't have the right word here but the idea...
Is this another one of those 'it really doesn't change the outcome' things?


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## grapeman (Dec 1, 2008)

The phenylthalene is not needed for the test when using the pH meter.


That is incorrect suprasteve. The pH of 8.2 is over ten timesas basic as 7.0. They aren't even close. 8.2 is the value that is absolutely needed. That is the point at which the phenylthalene changes the color of the solution(even though the phenyl isn't needed when using the pH meter).
Maybe PeterZ can explain the logarythmic thingy to you for pH (all I know is that each full point that the scale moves, you multiply it by 10- move down from 7.0 to 6.0 and it is 10 times as acidic. From 7.0 to 5.0, it is 100 times as acidic).


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## Jwhelan939 (Dec 1, 2008)

Ok, I had no idea I didn't need the phenylthalene to test this way. Will it alter my reading if I added it?


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## suprasteve (Dec 1, 2008)

appleman: correct, but a pH of 3.5, which I will say is 'correct' for wine (not really, just humor me on this for example's sake



) isnearly 1000 times more acidic than 8.2 is basic. I learned back in chemistry that phenolphtalein (sp?) doesn't change color at exactly 7 (hence the 8.2 discussed), but comparatively it is close enough to show a change in pH for many situations that don't have to be THAT exact. In my labs we used it to show a switch from acidic to basic, even though the switch (which occurs at 7)really precedes the change in color (which occurs at8.2). I was wondering if the titration kit bases off of 7 or 8.2 for the same reason, didn't know if it takesinto account that small percentage difference or not. I'm kinda leaning towards that 'doesn't affect anything' side since the concentration at 8.2 compared to say 3.5 is probably negligibly different from the concentration from 7 to 3.5. Again, I might be trying to bring waay too much chemistry into the matter


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## JWMINNESOTA (Dec 1, 2008)

Thinking along these lines, remember, while 7 is neutral on the pH scale, we are not titrating the must to find strength, but rather the amount of acid (two totally different test) The reagents will react at 8.2, BUT, it may very well take more, or lessNaOH to reach this point, the amount used is what gives your answer, not the pH, 8.2, that it does so at. *Edited by: JWMINNESOTA *


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## gaudet (Dec 1, 2008)

Makes perfect sense to me now that you put it out there. Why do you need an indicator? (semantics???



) When the pH reaches 8.2 you are done........


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## JWMINNESOTA (Dec 1, 2008)

Most experience people doing a T.A. wont use a pH meter, they go by the color change. It can be hard to determine in red wines, even different results from one person to the next as to when they see the change, pH is a tool to verify it did indeed happen. (It happened at 8.2 even if your eyes didn't detect it)


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## PeterZ (Dec 2, 2008)

If you are using a pH meter you don't need to add the indicator. Phenolphthalein changes color at pH 8.2. Another couple of commonly used indicators, methyl purple and methyl orange, change color at pH 4.3. Used together with a host of equations, they can be used to quantify the concentration ofH+, HCO3- (bicarbonate), CO3-2 (carbonate), and OH- (hydroxyl) ions in an aqueous solution. At pH 8.2 all H+ ions have been eliminated. The quantity offree and combined - but available - H+ ions isthe definition of TA (total acidity).


This is why pH cannot be used to determine TA directly. TA deals with ions that are not considered in pH testing. pH is just the negative log of the free H+ concentration.


I disagree with JW in that I think most commercial wineries are using pH meters to determine TA. They are using calibrated burettes that read to 0.1 ml of titrating solution (NaOH) and probably, as they approach pH 8.2, add the solution one drop at a time. That's how I did it in a lab setting. In the field I used phenolphthalein, because I didn't have all of the stands and holders that are standard in a lab.


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## grapeman (Dec 2, 2008)

I use the type setup Peter describes here. I go fairly quickly adding NaOH until the meter gets above 7.0 and then slow down. The reaction can happen so fast that going from 7.8 to 8.2 can happen with just one more drop. The graduated burette tells me how many mls have been added. And yes, the burette is graduated in tenths of a ml. 


I know I have tested with the visual test several times and verified with the meter. I typically go well past the correct point because I can't distinguish the color chage well. I trust the meter a lot more than my eyes especially if I have recently calibrated the meter.


More than most guys need but here is what I use(except my ph meter is a benchtop model).
http://valleyvintner.com/Merchant2/merchant.mv?Screen=PROD&amp;Product_Code=TE-15-3970&amp;Category_Code=TE






*Edited by: appleman *


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## JWMINNESOTA (Dec 2, 2008)

PeterZ said:


> I disagree with JW in that I think most commercial wineries are using pH meters to determine TA. They are using calibrated burettes that read to 0.1 ml of titrating solution (NaOH) and probably, as they approach pH 8.2, add the solution one drop at a time. That's how I did it in a lab setting. In the field I used phenolphthalein, because I didn't have all of the stands and holders that are standard in a lab.




Your probably correct there Peter, I should of been clear that most people in my industry (dairy) dont use the pH meter. In wine im sure its needed due to the color of the wine,I know I need to use it on my wine even though I run these test daily at work.


Nice set up Appleman, im sure we would all get giddy playing around in your wine making area!


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