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From their standard reduction potentials, which of the following metals would you expect to dissolve in \(\mathrm{HCl}\) by the reaction \(\mathrm{M}+n \mathrm{H}^{+} \rightarrow \mathrm{M}^{n+} \rightarrow \frac{n}{2} \mathrm{H}_{2}: \mathrm{Zn}, \mathrm{Fe}, \mathrm{Co}, \mathrm{Al}, \mathrm{Hg}, \mathrm{Cu}, \mathrm{Pt}, \mathrm{Au} ?\) (When the potential predicts that the element will not dissolve, it probably will not. If it is expected to dissolve, it may dissolve if some other process does not interfere. Predictions based on standard reduction potentials at \(25^{\circ} \mathrm{C}\) are only tentative, because the potentials and activities in hot, concentrated solutions vary widely from those in the table of standard potentials.)

Step by step solution

01

Understand the Reaction

We are determining which metals can dissolve in HCl by reacting with hydrogen ions (H鈦�) to form the corresponding metal cation (M鈦库伜) while releasing hydrogen gas (H鈧�). This happens spontaneously when the metal is above H鈦� in the electrochemical series.

02

List Standard Reduction Potentials

List the standard reduction potentials for the half-reactions of each metal with H鈦� and compare to the reduction potential of H鈦� to H鈧�, which is 0 V. The standard reduction potentials are Zn(-0.76 V), Fe(-0.44 V), Co(-0.28 V), Al(-1.66 V), Hg(+0.85 V), Cu(+0.34 V), Pt(+1.20 V), and Au(+1.50 V).

03

Identify Metals Above H鈦� in the Series

If a metal has a more negative reduction potential than H鈦� to H鈧� (0 V), it will dissolve in HCl. Compare each metal's potential: Zn, Fe, Co, and Al have reduction potentials less than 0 V, indicating they will dissolve.

04

Verify Results with Potentials

Since Zn (-0.76 V), Fe (-0.44 V), Co (-0.28 V), and Al (-1.66 V) have negative values, they will spontaneously oxidize (lose electrons) in HCl, encouraging the reduction of H鈦� to H鈧�. Metals with positive potentials, such as Hg, Cu, Pt, and Au, will not spontaneously dissolve.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Understanding Standard Reduction Potential

The concept of standard reduction potential ( E掳 ) is central to predicting the behavior of metals in redox reactions. It is a measure of the tendency of a chemical species to acquire electrons and thereby be reduced. Standard conditions for these potentials involve a concentration of 1 M, a pressure of 1 atm for gases, and a temperature of 25掳C. These conditions simplify comparisons.

• For example, the reduction potential for the conversion of hydrogen ions ( H鈦� ) to hydrogen gas ( H鈧� ) is set at 0 V.
• When a metal has a standard reduction potential more negative than 0 V, it suggests a stronger tendency to lose electrons (oxidize) than to gain them (reduce).
• This characteristic is important in determining whether a metal will dissolve in an acid like HCl, where H鈦� acts as a reactant.

Understanding the standard reduction potential allows us to predict the direction and spontaneity of redox reactions.

Metal Reactivity and its Implications

Metal reactivity is linked closely with its position in the electrochemical series. A metal with a higher reactivity will typically have a more negative standard reduction potential. This feature means the metal is more likely to lose electrons and less stable in its elemental form.

• Aluminum ( Al ), with a highly negative reduction potential of -1.66 V, is quite reactive.
• Zinc ( Zn ) and iron ( Fe ) also exhibit reactivity due to their negative potentials, -0.76 V and -0.44 V, respectively.
• Contrastingly, metals like platinum ( Pt ) and gold ( Au ) have positive potentials (1.20 V and 1.50 V), marking them as less reactive and prone to reduction rather than oxidation.

Reactivity not only determines a metal鈥檚 ability to dissolve but also influences its usefulness in applications like galvanic cells and corrosion resistance.

Basics of Redox Reactions

In redox reactions, reduction and oxidation occur simultaneously. One species undergoes reduction (gains electrons), and another undergoes oxidation (loses electrons). The term "redox" is derived from these simultaneous chemical changes. Understanding how these reactions occur is vital for comprehending why certain metals dissolve in HCl.

• Reduction is the process where a molecule, atom, or ion gains electrons, becoming more negative.
• Oxidation involves losing electrons and becoming more positive.
• In the context of the exercise, metals react with HCl when their standard reduction potentials are more negative than 0 V, leading them to liberate electrons that H鈦� ions can accept to form H鈧� gas.

These interactions form the basis of many natural and industrial processes, such as corrosion, combustion, and electrolysis.

Spontaneous Dissolution in Acid

Spontaneous dissolution occurs when a metal reacts with an acid without external influence. In this context, metals dissolve in HCl if they have the necessary reactivity and an appropriate standard reduction potential.

• If a metal's standard reduction potential is lower than 0 V, it spontaneously undergoes oxidation in HCl.
• This process forms metal cations and releases hydrogen gas.
• For instance, zinc and iron easily dissolve as they facilitate the reduction of H鈦� to H鈧�, while gold and platinum resist dissolution due to their positive potentials.

Understanding spontaneous dissolution is crucial in various fields, such as metallurgy and chemistry, where controlling metal corrosion and converting metal ores are regular practices.