chemistry help needed

[wood1954]

I'm trying to make my own .1N sodium hydroxide solution to do TA testing. From what i can find i should be able to add 2 grams of sodium hydroxide to 500 ml of water. It should be a ph of 14, but i can only get it to 12.9.
It took 24 ml of this solution to get my 30 ml wine sample to 8.2 for a TA of 12g/l. Is my math or process correct? I'm using old distilled water for my solution could that be an issue?

 

[BernardSmith]

I am most definitely not a chemist, but I wonder if the distilled water might be the problem. Did you check its pH? I see from Prof Google that when distilled water is exposed to air the pH can range from 5.5 to 6.9 , so if the water was more acidic, would that prevent the base from hitting 14?

 

[Jim Welch]

not a chemist either but wonder if it is possible the sodium hydroxide could be "weak" so to speak? Just a guess

 

[Rice_Guy]

There is some impurity in the NaOH we used in the QA lab, therefore we always “calibrated” a carboy of alkali for titrations using salicylic acid and weighing to 0.001 gram. Yes carboys, so we had a CO2 trap on the bung since it reacts with alkali.

For home use, your standard error is one drop/ roughly 0.05 gram of solution. For home use the working goal is 0.5 to 0.7% TA. Using a reagent grade NaOH pellet and ignoring the contaminant is good enough for estimated error. ,,,,, Grandpa never had any chemistry and could make acceptable wine. ,,,, My look at running TA is that it gives a reference point on where you are versus the rest of the world of wine. The exact number doesn’t matter as much as understanding what direction tastes are coming from. ,,,, I sin comming from a lab background. There are folks in the Vinters club who are better wine makers than me because they can taste the changes in real time.

I would guess the pH probe/ meter has more to do with a measured pH of 12.9 than the reagent and distilled water. ,,,, humm have I ever measured anything that was 14.0? ,,, , , , NO! ,,, 14 is a theoretical number saying ten to the 14th power. Likewise I have never measured a pH of 0

 

[Hazelemere]

I'm trying to make my own .1N sodium hydroxide solution to do TA testing. From what i can find i should be able to add 2 grams of sodium hydroxide to 500 ml of water. It should be a ph of 14, but i can only get it to 12.9.
It took 24 ml of this solution to get my 30 ml wine sample to 8.2 for a TA of 12g/l. Is my math or process correct? I'm using old distilled water for my solution could that be an issue?

A pH meter can't read to pH 14. 0.1 N sodium hydroxide is pH 13 so your solution sounds ok to use. Old distilled water is fine.

 

[wood1954]

Thanks for all the good answers, i feel better about my results now.

 

[rsportsman]

I'm trying to make my own .1N sodium hydroxide solution to do TA testing. From what i can find i should be able to add 2 grams of sodium hydroxide to 500 ml of water. It should be a ph of 14, but i can only get it to 12.9.
It took 24 ml of this solution to get my 30 ml wine sample to 8.2 for a TA of 12g/l. Is my math or process correct? I'm using old distilled water for my solution could that be an issue?

Should be pH 13, but most pH meters don't do well above 12 anyway so don't worry too much. I get 6.0 g/L TA from your numbers:
(24 mL * 0.1 N / 30 mL sample) * 75 g/eq tartaric acid (not 150 g/mol because there's two protons per molecule; and N is in units of equivalents per L).

 

[wood1954]

Should be pH 13, but most pH meters don't do well above 12 anyway so don't worry too much. I get 6.0 g/L TA from your numbers:
(24 mL * 0.1 N / 30 mL sample) * 75 g/eq tartaric acid (not 150 g/mol because there's two protons per molecule; and N is in units of equivalents per L).

I was wondering about my math. That would explain why this vintage is so much more drinkable.

 

[ChuckD]

Should be pH 13, but most pH meters don't do well above 12 anyway so don't worry too much. I get 6.0 g/L TA from your numbers:
(24 mL * 0.1 N / 30 mL sample) * 75 g/eq tartaric acid (not 150 g/mol because there's two protons per molecule; and N is in units of equivalents per L).

Ok. So I routinely see TA reported as g/L and %. What is 6g/L expresses as %TA? I think I know but I’m questioning my placement of the decimal point.

 

[Rice_Guy]

Some express TA as a percent (gm per 100ml) and others as gm per 1000ml (liter)

 

[ChuckD]

Some express TA as a percent (gm per 100ml) and others as gm per 1000ml (liter)

So as a percent it is .06%?

 

[sour_grapes]

So as a percent it is .06%?

No, 0.6%.

 

[ChuckD]

No, 0.6%.

Ok. So I ran the TA on my rhubarb wine. 10 ml sample with 10ml of distilled water. I used 0.2N sodium hydroxide.

(13ml x 0.2 x 0.75)/10 = 0.195

So TA is 0.19% or 19g/L

Is that correct?

 

[Rice_Guy]

Using a 15ml sample one ml of 0.2 N should represent 0.1% titratable acidity. However you used a 10ml sample. ,,, I get .87% TA.

A clean rhubarb juice usually is 1.25% TA, not a lot of water in your wine.

 

[ChuckD]

Using a 15ml sample one ml of 0.2 N should represent 0.1% titratable acidity. However you used a 10ml sample. ,,, I get .87% TA.

A clean rhubarb juice usually is 1.25% TA, not a lot of water in your wine.

What equation are you using to get .87% from my numbers? Please show your math.

 

[Rice_Guy]

The formula is: TA = volume NaOH * Normality * 75 / ml of sample.

Chuck, I didn’t use a formula last night laying in bed, I sinned. The kit umpteen years ago was designed to give 0.1% TA per ml of 0.2N. I took 2/3 of ml.

A TA of 0.19% would be very low and suggest that this rhurbarb was diluted 1:9 when made which would be very very very thin for a wine. A TA of 19.5% or 195 gm per liter doesn’t make sense.

 

[ChuckD]

The formula is: TA = volume NaOH * Normality * 75 / ml of sample.

Chuck, I didn’t use a formula last night laying in bed, I sinned. The kit umpteen years ago was designed to give 0.1% TA per ml of 0.2N. I took 2/3 of ml.
View attachment 99913
A TA of 0.19% would be very low and suggest that this rhurbarb was diluted 1:9 when made which would be very very very thin for a wine.

That’s the formula I used. So my TA of 19.5g/L is correct. In my head I always want to move two decimal points to report it as a percentage so I think I messed up.

Expressed as % that would be 1.95% TA. There is almost no water in the wine and it tastes like sucking on a rhubarb stalk.

 

[Rice_Guy]

Going back to the original post wood was making 0.1N alkali. I get 0.97% which is believable

 

[ChuckD]

Going back to the original post wood was making 0.1N alkali. I get 0.97% which is believable

But using my numbers for my wine using 0.2N sodium hydroxide in your equation the result is 19.5. I just found a TA calculator on the Vinmetrica website that gives me a result of 19g/L. So i assume I’m on the right track here.

What am I missing? And What is 19g/L expressed as %TA?

Edited to correct my math ( I had 0.75 as the constant in the equation I had originally used).

 

[rsportsman]

19 g/L is 1.9%TA