Question 6 - Is Curdling of Milk a Physical or Chemical Change? - Questions at the end of the chapter - Chapter 5 Class 7 - Changes Around Us: Physical and Chemical (Curiosit

Last updated at July 13, 2026 by

Q6
Question

Is curdling of milk a physical or chemical change? Justify your statement.

📚 Concept: 5.2 A Substance May Change in Appearance and Not Remain the Same!
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Answer
Curdling of milk is a chemical change .

Justification:

  • When milk turns into curd, a new substance (curd / yogurt) is formed.
  • Curd has very different properties from milk — different taste (sour), different texture (semi-solid), different smell.
  • The change is caused by bacteria (lactobacilli) that ferment milk sugars (lactose) into lactic acid .
  • This is a chemical reaction .
  • The change cannot be reversed — once milk has curdled, you cannot get fresh milk back from it.

→ New substance + new properties + irreversible → classic chemical change.

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