How would you show that setting of curd is a chemical change?

Demonstrating that the setting of curd involves a chemical change can be explained with these points:

1. Chemical Transformation:
– Bacteria, like Lactobacillus, introduced into milk initiate a chemical reaction. These bacteria ferment lactose (milk sugar) present in the milk, converting it into lactic acid through a process called fermentation. The chemical equation for this change is:
C₆H₁₂O₆ (lactose in milk) → 2C₃H₆O₃ (lactic acid)

2. Alteration in Composition:
– This conversion of lactose into lactic acid signifies a change in molecular composition, indicating a chemical transformation.

3. Physical Changes:
– Simultaneously, curdling occurs due to the interaction of lactic acid with milk proteins (casein), leading to the coagulation of proteins and the formation of curd—a physical manifestation resulting from the chemical reaction.

To showcase the chemical change in setting curd:

– Highlight the conversion of lactose into lactic acid by bacteria, revealing a chemical transformation.
– Emphasize the modification in milk’s composition through the production of lactic acid.
– Discuss the physical outcome of curdling, demonstrating the link between the chemical reaction and the visible formation of curd.

These aspects collectively illustrate that the setting of curd involves a chemical change due to the conversion of lactose into lactic acid, resulting in alterations in milk’s composition and the formation of curd as a physical manifestation.