Physical vs Chemical Changes

Question 1

A student mixes a clear solution of sodium bicarbonate with a clear solution of acetic acid. Before mixing, both solutions are colorless and at room temperature. After mixing, the mixture bubbles vigorously, the temperature rises about 2°C, and a white solid forms. Which statement best describes what happened?

Accepted Answer

A chemical reaction occurred, producing new substances.

Answer

The substances dissolved each other, forming a homogeneous solution.

Answer

No chemical reaction occurred; the substances simply mixed together.

Answer

Only a physical change occurred because the temperature increased slightly.

Question 2

During electrolysis of an aqueous copper(II) sulfate solution using copper electrodes, copper metal is deposited on the cathode and the solution remains blue. Which statement correctly identifies the type of change occurring at the cathode and an observable sign that a chemical reaction has taken place?

Accepted Answer

Chemical change; metallic copper is deposited as a reddish‑brown solid on the cathode.

Answer

Chemical change; the blue color of the solution fades to colorless, indicating a reaction.

Answer

Physical change; oxygen gas bubbles are observed at the cathode, showing a phase change.

Answer

Physical change; copper ions simply migrate to the cathode without forming any new substance.

Question 3

During the electrolysis of aqueous copper(II) sulfate using copper electrodes, which observation most clearly shows that a chemical reaction has taken place?

Accepted Answer

Copper metal is deposited on the cathode

Answer

The temperature of the solution increases slightly

Answer

The electrical conductivity of the solution improves

Answer

The blue color of the solution remains unchanged

Try three questions

During the electrolysis of aqueous copper(II) sulfate using copper electrodes, which observation most clearly shows that a chemical reaction has taken place?

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