Question

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?

Answer 1

Hint:The pH of any solution measures the hydrogen ion concentration of the solution and the pH values range from 0 to 14, with pH 0 being the most acidic solution while pH 14 being the value for the most basic solution. Milk is converted to curd due to the decrease of pH.

Complete answer:
A.Milk is an emulsion that consists of fat droplets being suspended in the aqueous medium. When the milk coagulates, then curd is obtained. When the pH of milk is at 6 then it gets spoiled easily and gets unfit for drinking. To prevent the milk from being spoilt, the milkman adds a small amount of baking soda to the fresh milk to avoid the milk from getting spoilt by shifting the pH to an alkaline range which is above pH 7.
B.This milk takes take to set curd because the curd is nothing but spoilt milk and when the pH of milk is not in the acidic range and this is due to the reaction of baking soda with the acid of the medium that leads to the liberation of carbon dioxide and thus the acid present in the is neutralized and the curd does not set.

Note:
The pH of normal milk ranges from $6.5$ to $6.7$ at room temperature of 25 $^{\text{0}}\text{C}$. Due to the acidic nature of milk, it cannot be digested by all and hence those people prefer to plant planned milks whose pH value is higher than the pH value of milk and falls in the basic range and are hence more easily digested.