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Chapter 18: Problem 121

When aluminum foil is placed in hydrochloric acid, nothing happens for the first 30 seconds or so. This is followed by vigorous bubbling and the eventual disappearance of the foil. Explain these observations.

Short Answer

Expert verified
The initial delay in the reaction between aluminum foil and hydrochloric acid is due to the presence of a stable aluminum oxide layer on the surface of the aluminum. Once the hydrochloric acid breaks through this layer, it reacts with the aluminum, producing aluminum chloride and hydrogen gas. This reaction causes vigorous bubbling, and eventually, the aluminum foil disappears as it completely reacts with the hydrochloric acid.

Step by step solution

01

Identify the chemical reaction

We need to identify the chemical reaction that occurs between aluminum (Al) and hydrochloric acid (HCl). The reaction is as follows: \[ 2Al (s) + 6HCl (aq) \rightarrow 2AlCl_{3} (aq) + 3H_{2} (g) \]
02

Understand the role of the aluminum oxide layer

Aluminum is reactive, but it is covered with a thin and stable oxide layer (Al2O3) that forms when aluminum is exposed to air. This oxide layer protects the underlying aluminum from further reaction with air and other substances. We need to recognize that this oxide layer is the reason nothing happens when the aluminum foil is initially exposed to hydrochloric acid.
03

Examine the initial delay

In the first 30 seconds or so, as the hydrochloric acid comes into contact with the aluminum foil, it will first react with the aluminum oxide layer. The oxide layer is very thin, but it is also very stable, so it takes some time for the hydrochloric acid to break through this protective layer.
04

Investigate the vigorous bubbling and disappearance of the foil

Once the hydrochloric acid breaks through the oxide layer, the aluminum will begin to react with the hydrochloric acid, producing aluminum chloride and hydrogen gas: \[ 2Al (s) + 6HCl (aq) \rightarrow 2AlCl_{3} (aq) + 3H_{2} (g) \] The vigorous bubbling that we observe is due to the rapid production of hydrogen gas. As more aluminum is exposed to the hydrochloric acid and more hydrogen gas is produced, the reaction becomes more and more vigorous. Eventually, all of the aluminum completely reacts with the hydrochloric acid, leading to the disappearance of the foil.
05

Summary

The initial delay in reaction between aluminum foil and hydrochloric acid is due to the stable oxide layer on the surface of the aluminum. Once the hydrochloric acid breaks through this layer, it reacts with the aluminum to produce aluminum chloride and hydrogen gas, leading to vigorous bubbling and the eventual disappearance of the aluminum foil.

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Most popular questions from this chapter

What volume of \(\mathrm{F}_{2}\) gas, at \(25^{\circ} \mathrm{C}\) and \(1.00 \mathrm{~atm}\), is produced when molten \(\mathrm{KF}\) is electrolyzed by a current of \(10.0 \mathrm{~A}\) for \(2.00 \mathrm{~h}\) ? What mass of potassium metal is produced? At which electrode does each reaction occur?

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An unknown metal \(\mathrm{M}\) is electrolyzed. It took \(74.1 \mathrm{~s}\) for a current of \(2.00 \mathrm{~A}\) to plate out \(0.107 \mathrm{~g}\) of the metal from a solution containing \(\mathrm{M}\left(\mathrm{NO}_{3}\right)_{3} .\) Identify the metal.

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