acid test question

[reisjdmd]

a little long winded, but interesting


01-used two big cans of "chenin" concentrate diluted to 5 gallons[ok]
02-SG measured 1.074 [boo]
03-raised SG to 1.092 with sugar [yeah]
04-used yeastfrom my supplier [ok]
05-fermented to completion with SG 0.992 [yeah]
06-transfer to secondary [logical]
07-taste it; decent but somewhattart [no problem]
08-vinometer 11.2 vol% [yeah]
09-pH is 2.88 [hmmmmm]
10-TA is 0.45 [hmmmmmmmm]


question: i use a bicarbonate method to measure total acid. ostensibly, the 0.45 is trueTA. however, this is the first time i have used this method, and the instructions say that this 0.45 is the tartrate only. they continue that to arrive at malate, i multiply by 1.17. a similar procedure gives me citrate.
i contacted my supplier and he says that the 0.45 is the TA that is used by all wineries, and is tartrate only. my problem is that i cannot imagine a trueTA [all 3 acids]of only0.45 giving me a pH of 2.88. i could imagine thispHbeing due to contribution fromall three acids, butthen i would expect the true TA to be higher. however, if i try to generate a true total TA by taking 0.45 [measured]+ 1.17x0.45 [calculated]+ 1.25+0.45 [calculated] it seems i get a true TA that is non-sense.
any thoughts???? sorry this is wordy!

 

[pelican]

What exactly is a bicarbonate method to measure total acid???

Have you tried to correlate that method's results with say, using the Sodium Hydroxide to neutralize the acid and measure when/where that happens with PH meter? (8.2 I think is the magic number for that, then count the mls of NaOH used, #X mls is .X% TA - but verify as I am going by memory)

If two separate methods of measure arrive at the same result, there you go. If you get two "very" different results, then one is quite likely wrong.

(I am curious on what the bicarbonate method is, because, I like to try new things and also to verify my own results from other methods too)

 

[PeterZ]

Sodium bicarbonate (NaHCO3) is itself a weak base. It is one member of the carbonate family that includes carbonic acid (H2CO3), X bicarbonate (XHCO3), and X carbonate X2CO3. X can be any element in theGroup Iof the Periodic Table, i.e. lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), or francium (Fr). Obviously, we only deal with the sodium and potassium salts.


What form the carbonate takes is a function of pH. I'm working from memory here, so bear with me. Below pH 4.3 the dominant form isCO2 because in aqueous solution H2CO3 decomposes intoCO2 + H2O. They carbonate soda by mixing H2CO3 withwater at the bottling plant.


From pH 4.3 to ~6.4 there is a mixture of CO2 and HCO3-, with the CO2 dominant. From 6.4 to 8.2 the relationship reverses and HCO3- predominates. By pH 8.2 all of the CO2 is gone and CO3-2 is starting to form. HCO3- is still the dominant ion until pH 10.3 when CO3-2 dominates. By pH 12 all of the HCO3- is gone and CO3-2 is the only carbonate family ion left.


Given all of those variables, I think using bicarbonate in the test is unusual. Can you post the test procedure?

 

[reisjdmd]

since i am theonly person in the civilized world that does not have a digital camera, i cannot post pictures. howver, the method i used is a kit i purchased locally. the theory is remakably straight forward, and the method is easy and fast [all parts supplied with kit].
use a test tube with a 2 hole rubber stopper on top. the first hole is connected to a clear plactic hose that goes from the top of the stopper to a upright"scale." there is a trap filled with water in this tube.think of a clear tube that goes to the bottom of an old style thermometer. the waterwill go up the tube just like the red stuff goes up a thermometer. whereas heat pushes up the red stuff, it is carbon dioxide that pushes up the water.remember that the water is connected to the top of the test tube to one of the holes in the stopper.
place about1 tsp baking soda in the test tube. take a 1 cc syringe [tuberculin type or insulin type-comes with kit] and fill it to the 1 cc mark with the test liquid. push the tip of the syringe into the second holeof the rubber stopper. make sure it is a tight fit. quickly squeeze the test liguid into the test tube. bubbles immedicately form. the more acid, the more bubbles. these bubbles force the water column "up the thermometer" to give a final reading. sounds complicated but actually very simple and logical. more acid, more gas, higher column of water.
my originalquestion can be simplifies as follows: is it reasonable that a 0.45tartrate solution [if that is the only acid]can give a 2.88 pH reading??

 

[reisjdmd]

2 quick additionalthoughts


to visualize this, consider the air lock on top of the secondary. the carbon dioxide that pushes the water through the lock is doing the same thing that the test system under discussion is doing. if you had only baking soda in the secondary and if you could quickly squirt acid into the secondary, then you would see the water in the air lock rise, the total rise being proportional to the total acid injected.


also, i'm going to get some pure tartaric acid. i already have acid blend. if i prepare from each a solution that measures 0.45 by this test, i can do pH readings on each and compare the results. takes me back to the undergraduate days of being a chem major. [wow, that was so long ago we still had to take a course in alchemy-taught in latin, by a wizard]

 

[grapeman]

Since you have the pH listed as 2.88 I am assuming you are using a digital meter. Quick question - did you calibrate the meter before the test? If not it could be off.


I don't think it is likely that you would have that low a pH with that small amount of TA. If it was a really strong acid, maybe- but I don't think you have any strong acid in there. Check the meter if you didn't calibrate it- they can get off quite a bit when not in use.

 

[reisjdmd]

appleman
i agree completely with what you say.you hit the nail on the head. i am concerned about my pH meter. either the meter is off, or my bufffer is outdated. here's what i did, and i hope someone can help me.
i prepared two solutions, each of 0.45 TA. pure tartaric acid and anacid blend.the pH for the tartrate was 2.48; for the blend was 2.88.
i think my meter is off [probably becauseof the buffer]. can someone prepare a 0.45 TA of either pure tartrate or the blend and tell me the equivalent pH readings?
note, i think i used 1/4 level teaspoon/8 ozwaterto get my 0.45 solution. [since doing this, i got my microbalance from taiwan, so in the future i can do actual weights to within 0.1 gramof powder, not volume with kitchen measuring spoons]

 

[grapeman]

I think you need to calibrate the meter. Use two buffer solutions and following the directions calibrate the meter. I use 4.01 and 7.01 solution for mine. You need the two solutions to get it calibrated properly. I don't have my instructions here so I can't check my procedure, but you should follow yours anyway. I don't quite follow what you are trying to accomplish, but I certainly am not a chemist. Maybe if PeterZ sees this he can help.

 

[JWMINNESOTA]

Many "Chenin", or Chenin Blanc, are very high in tartaric acid, if my research is correct, when grown in warm climates and the T.A. is low, it will almost all be tartaric. Would be a good one to sparkle.


http://en.wikipedia.org/wiki/Chenin_blanc


www.chemistry-react.org/fileLibrary/doc/wineinfo.doc

 

[reisjdmd]

appleman
"who guards the guardians" [quis custodiet ipsos custodes]? in other words, who testsyour buffer to make sure it is ok? this is the problem facing all pH meter users. i also use the hungarian packets of pH 4.01 and 7.01, as you do. however, as i recall sitting here in the office, the un-opened packet has a 3 month shelf life; the opened a 2 week life.i am not loathe to purchase the packets on the net, but the S&H costs are kind of steep. therefore, being a natural born scrounge, i try to use the openedpackets i have as long as possible. however, how do i know if the aready opened packet of buffer is still good?? enter the external standard.
if i know what the pH reading is supposed to be of a cheap,standard, easy to make and storesolution, then i can check my pH meter every time i use it [after calibrating with buffer]. my thought is that everyone has pure tartaric acid crystals. these are very cheap and very stable. it takes only a momentto make a 1 cup soultion of 8oz water to which is added 1/4 leveltsp tartaric acid.if i know the pH of this ought to be "X", and if i test it with my meter and get a reading of "X", then all is well. if my meter reading is other than "X", i better use a new buffer or clean the electrode or change the battery. i am asking if a forum memeber that knows his pH meter is accurately calibrated would be so kind as to take 1/4 level tsp of tartaric acid crystals and dissolve them in 8 oz of distilled water and take a pH reading and post the result. what would be even more excellent is if the person could also test the TA of that solution. i think this information would be helpful to all pH meter users as an external reference standard, and it would only be a one time PITA for whoever does it.
hope this makes sense.

 

[grapeman]

I guess I am just not up on all this stuff, not being in the scientific community- chemistry in particular. I buy my buffer solutions in 60 ml bottles. That is plenty to last a year, and it keeps in the bottle for a year. Mine is expired now so I will replace in a while. I wouldn't be able to get the results you are looking for at this time. Maybe PeterZ could, I don't know.


You could get the results one time yourself by getting new buffer solutions. Calibrate the meter at that time and try mixing up the solution and testing yourself. Like you say, this would be a one time thing and shouldn't be that expensive to do yourself. I hope someone else can do it for you, but if not, just buy the small packets, calibrate and run the test. Good luck with it and let us know what you find out.

 

[PeterZ]

Well, I would not do it your way. Too much variability. I would use a graduated cylinder to measure 100 ml of water and add 1 g of tartaric acid to it for the standard. A 100 ml graduated cylinder is pretty easy to come by cheap, but how do you accurately measure 1 g? Go to a gun store and buy a reloader's powder scale for $25 or so. This can measure small quantities in grains (a grain is 1/7000 of a lb.) These scales are accurate to 0.1 grains. 1 gram is 15.4 grains.


Once a lab rat, always a lab rat.