Understanding Chemical Changes

Chemical changes are fundamental transformations where a substance changes into a new substance with different properties. This involves the breaking and forming of chemical bonds. In contrast, physical changes alter the form or appearance of a substance but not its chemical composition.

Let's analyze the given options to determine which one represents a chemical change.

Analysis of Options

We will examine each option and classify it as either a physical or chemical change.

• Cutting of hair: When hair is cut, its length is reduced, and its shape changes. However, the chemical composition of the hair material (primarily keratin protein) remains the same. This is a physical alteration.
• Greying of hair naturally: Natural greying of hair is a complex biological process. It involves changes in the production of melanin, the pigment responsible for hair color. As melanin production decreases or the type of melanin changes, the hair loses its color. This change in pigmentation involves chemical processes and alterations to the composition within the hair follicle and shaft, making it a chemical change.
• Swelling of resin in water: When resin is placed in water, it absorbs water and swells. This is a physical process where water molecules are absorbed into the resin structure, causing it to expand. The chemical composition of the resin and water remain unchanged. This is a physical change.
• Cutting of fruit: Cutting a fruit changes its size and shape. Similar to cutting hair, the primary act of cutting is a physical process. While exposing fruit to air after cutting can lead to subsequent chemical changes (like enzymatic browning due to oxidation), the cutting itself is a physical change.

Based on this analysis, natural greying of hair is the only option that involves a fundamental change in the chemical composition (pigmentation) of the substance.

Comparing Physical vs. Chemical Changes

Here's a quick comparison:

The process of hair greying involves complex biochemical reactions affecting melanin synthesis and distribution within hair cells, which is clearly a chemical transformation.

Conclusion on Chemical Change Identification

Identifying whether a change is chemical or physical depends on whether new substances with different properties are formed. Cutting and swelling are changes in form or state. Greying of hair involves a change in the chemical substances that give hair its color.

Revision Table: Physical vs. Chemical Changes

Additional Information on Chemical Changes

Chemical changes are also known as chemical reactions. Evidence of a chemical change can include:

• Change in color (like greying of hair or rusting of iron)
• Production of gas (like bubbles when baking soda reacts with vinegar)
• Formation of a precipitate (a solid forming from liquids)
• Change in temperature (heat released or absorbed)
• Production of light

Natural greying of hair demonstrates a change in color due to underlying chemical processes affecting pigmentation.