Determination of %age acidity in milk

Titration

  • Equal volumes of acids and alkalis of the same strength will exactly neutralize each other.
  • The point of neutralization is determined by means of an ‘indicator’.
  • It gives one definite color in an alkaline medium and another color in an acid medium.
  • The indicator generally used is phenolphthalein which is colorless in acids and pink in alkali.
  • In finding the percentage of acid in milk, it is necessary to know the weight of the milk taken and the strength of alkali solution used.



  • The weight of milk by balance or by multiplying the specific gravity of milk by the number of ml of milk taken.
  • The strength of alkali used is tenth normal or decinormal (expressed as N/10).
  • 1 ml of N/10 alkali (NaOH) solution would just neutralize 0.009 g of lactic acid1To find out the percentage of acidity in milk when N/10 alkali is used, the number of ml of N/10 alkali necessary to neutralize the the acid in the amount of milk taken is multiplied by 0.009 and the product is divided by the weight of milk taken in grams and the quotient multiplied by 100.

 Calculation


The following formula represents the calculations
 
Now, supposing 1.7 ml of N/10 alkali solution were used to neutralize the acid in 10g of milk, the percentage of acidity in the sample of milk will be as follows:


Apparatus and reagents


  • Burette with a clamp and stand
  • Pipette
  •  Alkali solution (N/10 sodium hydroxide)
  •  Phenolphthalein solution (as an indicator)

 

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