TITRATION OF A LACTIC ACID IN A SAMPLE OF MILK
CH3-CHOH-COOH
SCOPE :
The scope of this laboratory experiment is to determine the amount of lactic acid presents in a
sample in order to determine the degree of acidity.
MATERIALS :
• NaOH solution with a known titre (0.4 N)
• Becker
• Burette with sensibility 0.1ml and 50 ml capacity with its support
• 250 ml of fresh milk
• phenolphthalein
METHODOLOGY:• We rinse the burette with titrant (NaOH), we take a known quantity of
milk and we add the indicator (phenophthalein).
• Then we begin to titrate our test substance by adding a more or less large amount of titrant (it depends on the color variation of the indicator.
• We proceed with this methodology until the color variation is constant for more than 30 seconds and very evident.
• We write down the volume of titrant used to reach our equivalent point. We’ll need it for theoretical calculations.
TABLE AND CALCULATIONS :
mole of lactic acid = 4,3*10^-3 [liters]*0,1001[mole/liters]=4,3*10^-4 [mole]
gr of lactic acid = 4,3*10^-4[mole] * 90,08 [gr/mole] = 3,88*10^-2[gr]
EQUIVQLENT POINT [ml] NaOH [0,1001 N] TITRATED VOLUME MOLAR MASS [gr/mol]4,3 4,3 25 90,08
Gr of acid lactic ppm acid lactic (part form million )3,88X10 -̂2 38,77
CONCLUSIONS:
Our sample of milk contains 1,55 gr/l of lactic acid and the S.H. degree > 6 indicates that it’s a good preservation milk.
IV A I.I.S CHEMICAL SPECIALIZATION
TEAM :
•ALBRA INVA
•CARUSO ANDREA
• BENTIVOGLIO TECLA
• MANGANI ILARIA
•CINCI RACHELE
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