Science & STEM

Souring of Milk Chemical Change: Quick Quiz

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This quiz helps you decide if the souring of milk is a chemical change and spot the difference from physical changes. Answer quick, real-life items and get instant feedback, then try our physical vs chemical change quiz, a broader chemical and physical changes quiz, or dive into chemical change questions.

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1What type of change is milk souring?
2Which microorganism is primarily responsible for souring milk?
3Which compound accumulates in milk as it sours, giving it a tart taste?
4Is the denaturation of milk proteins during souring reversible?
5How does the pH of milk change as it sours?
6Which component of milk primarily coagulates when it sours?
7Which class of reaction best describes the biochemical process of milk souring?
8Which indicator would turn red in the presence of sour milk?
9What laboratory measurement quantifies the total acid content in soured milk?
10Is the fermentation of milk generally exothermic or endothermic?
11After filtering curdled milk, which substance predominantly remains in the filtrate?
12How many moles of lactic acid are produced from one mole of lactose via homofermentative lactic acid fermentation?
Learning Goals

Study Outcomes

  1. Understand Chemical and Physical Changes -

    Grasp the core differences between chemical reactions and physical transformations such as melting and freezing.

  2. Differentiate Chemical vs. Physical Transformations -

    Learn to distinguish examples of chemical change from physical changes by evaluating observable properties and energy shifts.

  3. Identify the Nature of Milk Souring -

    Determine if milk souring is a chemical change by examining evidence like odor, color, and new substance formation.

  4. Analyze Melting and Freezing Examples -

    Break down common melting and freezing processes to understand reversible physical state changes in everyday life.

  5. Evaluate Evidence in States of Matter Transformations -

    Assess experimental clues and select appropriate criteria to confirm chemical reactions or physical processes.

  6. Apply Classification Skills in a Quiz Setting -

    Use your knowledge to successfully complete the physical vs chemical changes quiz and reinforce learning through interactive practice.

Study Guide

Cheat Sheet

  1. Core Definitions of Change -

    Chemical changes yield new substances with different compositions, while physical changes only alter form without changing identity (e.g., melting ice). This distinction is key when you ask "is milk sours a chemical change," because only bond rearrangements count as chemical. (Sources: American Chemical Society, Khan Academy)

  2. Why Milk Souring Is a Chemical Change -

    Souring milk involves bacteria converting lactose into lactic acid, creating new compounds and an irreversible pH shift, so milk souring is a chemical change. This classic example of a chemical change contrasts with physical transformations like freezing. (Sources: University of California Davis, ACS publications)

  3. Mnemonic for Identifying Chemical Changes -

    Remember "BONGO": Bond-breaking, Odor change, New substance, Gas evolution, Order change. Spotting two or more BONGO signs - such as the sour smell and new acid in milk - confirms a chemical change. (Source: Royal Society of Chemistry)

  4. Reversible vs. Irreversible Changes -

    Physical vs chemical changes quiz prep hinges on reversibility: melting and freezing changes are reversible physical changes, whereas milk souring is irreversible. Practice sorting scenarios - like dissolving salt versus burning paper - to sharpen your classification skills. (Sources: LibreTexts, ACS)

  5. States of Matter Transformations -

    Beyond liquid - solid transitions, recall gas→liquid (condensation) and solid→gas (sublimation) are physical changes without new chemicals. Use flashcards or a physical vs chemical changes quiz online to master these states of matter transformations. (Sources: Khan Academy, Purdue University Chemistry)

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Updated Feb 18, 2026