A milkman adds a very small amount of baking soda to fresh milk.
(a) Why does he shift the pH of the fresh milk from 6 to slightly alkaline?
(b) Why does this milk take a long time to set as curd?
Solution 1
(a) The milkman shifts the pH of the fresh milk from 6 to slightly alkaline because in alkaline condition, milk does not set as curd easily.
(b) Since this milk is slightly basic than usual milk, acids produced to set the curd are neutralized by the base. Therefore, it takes a longer time for the curd to set.
Solution 2
(a) Usually, milk is acidic, with a pH of 6. The milkman has added a very small amount of baking soda to the milk to make it alkaline, so that it will not become sour with the formation of lactic acid. The alkaline medium prevents the milk from changing into curd. This is the reason why the milkman has shifted the pH of fresh milk from 6 to slightly alkaline.
(b) The milkman has made the milk alkaline by adding baking soda. The alkaline medium of milk slows down the transformation of the milk into curd. The lactic acid produced undergoes neutralisation, so the milk takes a long time to set as curd.
