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A milkman adds a very small amount of ba...

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?

Text Solution

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(a) We know that fresh milk is slightly acidic due to presence of lactic acid and its pH is 6. Upon standing, its pH slowly secreases and it becomes sour since more of acid to released. The purpose of adding baking soda or sodium hydrogen carbonate `(NaHCO_(3))` is to make medium slighly alkaline. The base released will neutralise the effect of lactic aid present in milk. This will check the milk form getting sour.
(b) When milk sets as curd, it becomes more acidic and pH decreases. In the alkaline medium, it takes longler time to achieve acidic medium back so that milk may set as curd.
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