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How do I calculate total acid content?

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I need to calculate the total acid content of sauerkraut juice. The main acid in the juice is lactic acid.

I have already done the lab works, but I have difficulties to calculate the acid content by applying the right formula.

In the lab I took 5 ml sauerkraut juice and diluted it to 50 ml with distilled water. Then for the titration I used 0,1 n NaOH, phenolphtalein indicator, and made the titration with 5 ml aliquot. The consumption of the measuring solution was 0,65 ml.

I’d be very grateful if someone could help with the calculation.

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My knowledge of this comes from a far distant past but maybe I can help with the general idea?

The 5 ml aliquot (nice word) required 0.65 ml of 0.1 n NaOH to reach the endpoint

So, the number of equivalents in base = 0.1 x 0.65 E-3 L = 0.065 E-3 equivalents

Since 5 ml → 0.065 E-3 equivalents, 50 ml → 0.65 E-3 equivalents

Mass of lactic acid is 90 g/ mol

Therefor total mass of lactic acid in solution is 0.65 E-3 x 90 = 0.059 g

That seems low but since you started with 5 ml of juice and then diluted it, it might be OK

I would like to calculate it as a percentage of the 5 ml but I am unsure of the weight of 5 ml of s juice.

Maybe you know?

I would hazard a guess it is about the same as other juices and from here I gather that would be 5.2 g

So, % = 0.059 g / 5.2 g x 100 = 1.13%

Disclaimer: as a marine engineer, chemistry isn’t my strong suit and I advise you to double and triple check what I wrote to see if it makes sense to you.

And, Welcome to our forum,

Ocean

Edited by OceanBreeze
clear up unit conversion ml to L

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