jamesbsmith
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- Jun 29, 2013
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I have been working on a spread sheet which we will be releasing soon which allows wine makers to determine the acidity of their wines by either measuring acidity by titration or reading pH, which then gives the amount of acid / alkali they need to add to reach their desired acid level as well as the amount of campden needed when bottling.
I think that pH can be determined from titration (and visa versa), as long as the type of acid present in the wine / must is known (and if not an approximate value determined).
I believe that I have found out the way you can convert the values, but I just wanted to verify this before finalising and releasing my calcs.
If any of you are any good at chemistry / maths, would you be able to verify this:
pH from Titration
Determine number moles of NaOH present=
ml NaOH used in titration X Strength (M) of NaOH X Volume of Wine / Must
Determine number moles of Acid present=
2 moles NaOH react with 1 mole of malic acid
2 moles NaOH react with 1 mole of tartaric acid
3 moles NaOH react with 1 mole of citric acid
Therefore the main acid type in the wine needs to be known. Divide number of moles of NaOH by this value
To Calculate the pH from moles of a Weak Acid =
pH = -log (square root of ka [H+])
At present I have put the moles of acid in the place of [H+], or should that be moles of acid X 2 (for malic and tartaric), or moles of acid X3 for citric acid
Concentration of Acid from Known pH
By rearranging the formula above, for calculation of pH of a weak acid, to find [H+], the formula becomes=
Concentration of Acid = (10^-pH)^2 / ka
There are more than one ka value for acids which disassociate more than one H+ (i.e. all of the acids which may be present in wine). We are only interested in the first ka, as we are interested in the pH prior to any alkali being added.
The ka's for our three major wine acids are:
Citric Acid 0.00084
Malic Acid 0.000394
Tartaric Acid 0.001047
Again, I am unsure whether the value of [HA] gained needs to be multiplied by the number of moles of acid that would react with our titrated strong alkali NaOH.
Any help / advise on this would be great. The calcs are to accompany the excellent YoBrew Wine Calcs which I cannot take any credit for, but I use all the time and are a genius piece of work!
I think that pH can be determined from titration (and visa versa), as long as the type of acid present in the wine / must is known (and if not an approximate value determined).
I believe that I have found out the way you can convert the values, but I just wanted to verify this before finalising and releasing my calcs.
If any of you are any good at chemistry / maths, would you be able to verify this:
pH from Titration
Determine number moles of NaOH present=
ml NaOH used in titration X Strength (M) of NaOH X Volume of Wine / Must
Determine number moles of Acid present=
2 moles NaOH react with 1 mole of malic acid
2 moles NaOH react with 1 mole of tartaric acid
3 moles NaOH react with 1 mole of citric acid
Therefore the main acid type in the wine needs to be known. Divide number of moles of NaOH by this value
To Calculate the pH from moles of a Weak Acid =
pH = -log (square root of ka [H+])
At present I have put the moles of acid in the place of [H+], or should that be moles of acid X 2 (for malic and tartaric), or moles of acid X3 for citric acid
Concentration of Acid from Known pH
By rearranging the formula above, for calculation of pH of a weak acid, to find [H+], the formula becomes=
Concentration of Acid = (10^-pH)^2 / ka
There are more than one ka value for acids which disassociate more than one H+ (i.e. all of the acids which may be present in wine). We are only interested in the first ka, as we are interested in the pH prior to any alkali being added.
The ka's for our three major wine acids are:
Citric Acid 0.00084
Malic Acid 0.000394
Tartaric Acid 0.001047
Again, I am unsure whether the value of [HA] gained needs to be multiplied by the number of moles of acid that would react with our titrated strong alkali NaOH.
Any help / advise on this would be great. The calcs are to accompany the excellent YoBrew Wine Calcs which I cannot take any credit for, but I use all the time and are a genius piece of work!