Question

1. in photograph a, a coil of zinc metal is in a solution of sulfuric acid. in photograph b, a yellow solution of sodium chromate is being added to a colorless solution of silver nitrate. what clues in the photographs indicate that a chemical change is probably occurring? a. image b. image

Explanation:

For photograph A: Zinc (Zn) reacts with sulfuric acid ($\ce{H_2SO_4}$). The presence of bubbles (gas production) around the zinc coil indicates a gas is being formed, which is a sign of a chemical reaction (Zn + $\ce{H_2SO_4}$ → $\ce{ZnSO_4}$ + $\ce{H_2}$↑). For photograph B: Sodium chromate ($\ce{Na_2CrO_4}$, yellow) is added to silver nitrate ($\ce{AgNO_3}$, colorless). A brown/black precipitate (solid) forms, indicating a new substance (silver chromate, likely) is produced, which is a chemical change (precipitation reaction: $\ce{2AgNO_3 + Na_2CrO_4 -> Ag_2CrO_4↓ + 2NaNO_3}$). Signs like gas production (A) and precipitate formation (B) show chemical changes.

Answer:

In photograph A, the formation of gas bubbles (around the zinc coil in sulfuric acid) indicates a chemical change (gas production is a sign of a reaction, e.g., $\ce{Zn + H_2SO_4 -> ZnSO_4 + H_2↑}$). In photograph B, the formation of a brown/black precipitate (when yellow sodium chromate is added to colorless silver nitrate) indicates a chemical change (precipitation of a new substance, e.g., $\ce{2AgNO_3 + Na_2CrO_4 -> Ag_2CrO_4↓ + 2NaNO_3}$). These observations (gas production, precipitate formation) are clues of chemical changes.