[Nhcoll-l] Acidity in alcohol

[Margraf Nicolas]

Dear all,

The MHNC is a small natural history museum located in the hearth of the Jura Mountains in La Chaux-de-Fonds, Switzerland. The MHNC team is currently re-conditioning the alcohol collection, changing containers and alcohol using an 80% Ethanol solution. The team was told to check the acidity of the alcoholic solution as acidity is not good for the specimens but had trouble doing so.
Is a 9.6 mg/l acidity expressed as acetic acid too acidic? (12 mg/l in 96% Et-OH diluted to 4/5)
Additional questions:
The alcohol dealer was asked about the acidity of the 96% Ethanol he provides us with. The value he gave us is 12 mg/l of acidity expressed as acetic acid. We tried to calculate the pH based on that value and obtain a value of 4.23. Does that sound right?
We tried measuring the pH of the solution with both pH-paper and a pH-meter and found conflicting values. Is the pH-paper reading valid for an alcoholic solution? Or is the pH-meter value valid for an alcoholic solution?
A pH of 4.23 seems too acidic to preserve specimens so we tried to calculate the amount of Na2CO3 necessary to neutralize the 12 mg/l of CH3COOH and obtain 10.6 mg/l. Is it correct (and sufficient) to add this amount of Na2CO3 to every liter of our 96% Et-OH solution?
Any advice or help would be greatly appreciated.
Thanks,
Sincerely,
N
*****************************************
Nicolas Margraf
Collaborateur scientifique
Musée d'histoire naturelle de La Chaux-de-Fonds
Av. Léopold-Robert 63 - CH 2300 LA CHAUX-DE-FONDS
T +41 (0)32 967 60 71 - mhnc at ne.ch<mailto:mhnc at ne.ch>
www.mhnc.ch


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