Passage III

When a solid metal (M) such as iron(Fe), nickel (Ni) or zinc (Zn) is placed in an aqueous hydrochloric acid (HCI) solution, a reaction that produces H₂ gas occurs:

M + 2HCl → MCl₂ +H₂

Two experiments were conducted to study the production of H₂, in this reaction. The apparatus shown in the diagram below was used to collect the H₂ gas produced in each trial.

As H₂ was produced in the stoppered flask, it exited the flask through the outlet tube and displaced the water that had been trapped in the inverted graduated cylinder. (This displacement occurred because the H₂, did not dissolve in the water.) The volume of water displaced equaled the volume of gas (H₂ and water vapor) collected.

1. The apparatus was assembled, and 25 mL of a 4 moles/L HCI solution was poured into the empty flask.

2. A selected mass of Fe, Ni, or Zn was added to the flask and the stopper was quickly reinserted into the flask.

3. When H₂ production ceased, the volume of water that was displaced from the graduated cylinder was recorded.

The apparatus and its contents were kept at a selected temperature throughout Steps 2 and 3. The atmospheric pressure was 758 mm Hg throughout all 3 steps.

Experiment 1

In each trial, a selected mass of Fe, Ni, or Zn was tested at 30°C (see Figure 1).

Experiment 2

In each trial, 0.30 g of Fe, Ni, or Zn was tested at a selected temperature (see Figure 2).