The volume of hydrogen gas given off against time when an excess of zinc lumps is added to 100 cm³ of 1 mol l⁻¹ hydrochloric acid is shown - Scottish Highers Chemistry - Question 20 - 2019

To determine the appropriate graph that represents the volume of hydrogen gas given off when zinc powder reacts with hydrochloric acid, we need to analyze the setup and the differences in conditions compared to the initial scenario.

1. Reaction Dynamics: When zinc powder is added to 50 cm³ of hydrochloric acid, the reaction produces hydrogen gas. Given that zinc is in excess, the volume of gas produced will increase with time until the acid is fully consumed.

2. Expected Graph Behavior: In the original graph, the volume of hydrogen gas increases positively and then levels off, indicating that the reaction is complete. For 50 cm³ of hydrochloric acid, the volume of hydrogen produced will be less, but the initial steep rise followed by a plateau should still be observed.

3. Choosing the Correct Graph: Among the options presented (A, B, C, D), we analyze each to find:

• Graph A shows a linear increase with no plateau, which is not consistent with the expected behavior.
• Graph B also shows a linear rise but does not plateau, again not representative of the reaction completion.
• Graph C depicts a gradual increase followed by a plateau, which aligns with the reaction behavior.
• Graph D shows an initial increase but then a sudden jump, which is unrealistic for this reaction.

Thus, the correct choice that represents the volume of hydrogen gas given off when zinc powder is added to 50 cm³ of 1 mol l⁻¹ hydrochloric acid is Graph C.