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