Difficulty: Medium

Average Score: 73%

Which of the following demonstrates a chemical reaction involving water?

Rationale

Water produces gas when reacting with sodium metal.

This reaction is a clear demonstration of a chemical change, as it results in the formation of sodium hydroxide and hydrogen gas. The evolution of gas indicates a new substance is formed, which characterizes a chemical reaction.

A (Water and oil separate when combined) YOUR ANSWER

This scenario illustrates a physical change rather than a chemical reaction. While water and oil do not mix, they remain chemically unchanged and can be separated without altering their chemical structures. Thus, no new substances are formed in this process.

B (Water boils to produce steam at 100 degrees Celsius) YOUR ANSWER

Boiling water is also a physical change, where the water transitions from a liquid to a gaseous state (steam) due to heat. The chemical composition of the water (H₂O) remains the same throughout this process, indicating that no chemical reaction occurs.

C (Water dissolves sugar) YOUR ANSWER

The dissolution of sugar in water is a physical change. While sugar molecules disperse within the water, they do not undergo any chemical reaction; the sugar retains its original chemical structure. This process exemplifies solubility rather than a chemical transformation.

D (Water produces gas when reacting with sodium metal) CORRECT

This choice accurately describes a chemical reaction, where water reacts with sodium to produce sodium hydroxide and hydrogen gas. The release of gas signifies that new substances are formed, which is a definitive indicator of a chemical reaction taking place.

Conclusion

In summary, the reaction of water with sodium metal is the only option that demonstrates a chemical change, as it results in the formation of new substances through gas evolution. The other choices represent physical changes, where the original substances remain unchanged chemically. Understanding these distinctions is essential in identifying chemical reactions and their implications in various scientific contexts.

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