Question

The correct order of chemical reactivity with water according to clectrochemical scrics is (1) \(\mathrm{K}>\mathrm{Mg}>\mathrm{Zn}>\mathrm{Cu}\) (2) \(\mathrm{Mg}>\mathrm{Zn}>\mathrm{Cu}>\mathrm{K}\) (3) \(\mathrm{Cu}>\mathrm{Zn}>\mathrm{Mg}>\mathrm{K}\) (4) \(\mathrm{Cu}>\mathrm{Zn}>\mathrm{Mg}>\mathrm{K}\)

Short answer

The correct order is \( \mathrm{K} > \mathrm{Mg} > \mathrm{Zn} > \mathrm{Cu} \) (Option 1).

Step-by-step solution

Understand the Electrochemical Series

The electrochemical series ranks elements based on their tendency to be oxidized, with elements higher in the series being more reactive with water.

List Electrode Potentials

Consult the electrochemical series to find the standard electrode potentials for K, Mg, Zn, and Cu. Generally, potassium (K) has the highest reactivity followed by magnesium (Mg), zinc (Zn), and copper (Cu).

Identify the Correct Sequence

Match the given options with the order obtained from the electrochemical series. The correct order should begin with the most reactive element and end with the least reactive when reacting with water.

Select the Most Reactive Sequence

From the electrochemical series information, potassium (K) reacts most vigorously with water, followed by magnesium (Mg), then zinc (Zn), and lastly copper (Cu).

Verify the Answer

Confirm the correct order as \( \mathrm{K} > \mathrm{Mg} > \mathrm{Zn} > \mathrm{Cu} \). Check the list of given options to find the matching sequence.

Key concepts

chemical reactivity

Chemical reactivity describes how readily a substance undergoes a chemical reaction. In the context of metals reacting with water, it generally involves the element turning into its oxide or hydroxide along with the release of hydrogen gas.
In the electrochemical series, metals are ordered from those that lose electrons most easily (high reactivity) to those that lose them less readily (low reactivity).

• Highly reactive metals include potassium (K) and sodium (Na).
• Moderately reactive metals include magnesium (Mg) and zinc (Zn).
• Less reactive or noble metals include copper (Cu) and gold (Au).

This reactivity impacts industrial applications and safety considerations, as highly reactive metals can react violently with water or air.

standard electrode potentials

Standard electrode potentials (E°) measure the voltage developed by a half-cell in an electrochemical cell. These values are obtained under standard conditions: 298 K temperature, 1 M concentration of ions, and 1 atm pressure.
Electrode potentials indicate the tendency of a species to be reduced; higher (more positive) values mean a higher tendency to gain electrons and get reduced, while lower (more negative) values indicate a higher tendency to lose electrons and get oxidized.

• Potassium (K): Highly negative potential, meaning high oxidation tendency.
• Copper (Cu): Positive potential, indicating it is more inert and less likely to oxidize.

The standard electrode potentials thus help in predicting the direction of redox reactions and arranging the electrochemical series.

reactivity with water

The reactivity with water depends on how easily a metal can lose electrons and form positive ions. This is reflected in its position in the electrochemical series and its standard electrode potential.
Highly reactive metals like potassium (K) and magnesium (Mg) react vigorously with water:

• Potassium (K): Reacts immediately and explosively with water to form potassium hydroxide and hydrogen gas.
• Magnesium (Mg): Reacts more slowly, forming magnesium hydroxide and hydrogen.

Moderately reactive metals such as zinc (Zn) may react with boiling water, while less reactive metals like copper (Cu) do not react with water under normal conditions.

oxidation tendency

Oxidation tendency is the likelihood of an element to lose electrons during a chemical reaction. This tendency can be directly identified from the electrochemical series and standard electrode potentials.
Metals with a high oxidation tendency have a greater propensity to lose electrons and form cations. For instance:

• Potassium (K): High oxidation tendency; easily loses electrons to form K⁺ ions.
• Copper (Cu): Low oxidation tendency; does not easily lose electrons or react with water.

Understanding oxidation tendency helps predict reactivity patterns and is crucial for applications in battery design, corrosion prevention, and material science.