Problem 11 - Chemistry in 30 days

Question

The position of some metals in the electrochemical series in decreasing electropositive character is \(\mathrm{Mg}>\mathrm{Al}>\mathrm{Zn}>\mathrm{Cu}>\mathrm{Ag}\). What will happen if a copper spoon is used to stir a solution of aluminum nitrate. (a) The spoon gets coated with aluminium (b) An alloy of aluminium and copper is formed (c) No reaction occurs (d) The solution starts turning blue

Step-by-Step Solution

Answer

(c) No reaction occurs.

Step 1: Understanding the Electrochemical Series

The electrochemical series is a list of metals arranged in decreasing order of their ability to lose electrons; that is, their electropositive character. A more electropositive metal can displace a less electropositive metal from its salt solution.

Step 2: Identify the Metals Involved

In this problem, we have copper (Cu) as the spoon and aluminum (Al) in the nitrate solution. The electropostive character order is given as \(\mathrm{Mg} > \mathrm{Al} > \mathrm{Zn} > \mathrm{Cu} > \mathrm{Ag}\). Here, Al is more electropositive than Cu.

Step 3: Predict the Reaction Based on Electronegativity

Since aluminum is more electropositive than copper, aluminum cannot be displaced from its nitrate solution by copper. This means that copper cannot replace aluminum from \(\mathrm{Al}(\mathrm{NO}_3)_3\), so no chemical reaction will occur.

Step 4: Conclusion

Given that copper cannot displace aluminum due to its position in the electrochemical series, nothing will happen when the copper spoon is used to stir the aluminum nitrate solution.

Key Concepts

Electropositivity

Electropositivity refers to a metal's ability to donate electrons and form positive ions. Imagine it as the eagerness of an atom to lose an electron, akin to how some people are more willing to give away their spare change.

In the electrochemical series, metals are organized by their electropositivity, decreasing from the most eager electron donors to the least. This arrangement helps us predict how metals will behave in chemical reactions, especially those involving displacement.

• Electropositive metals, such as magnesium, sit at the top of this series.
• Less electropositive metals, such as silver, are lower down.

The idea is straightforward: the higher up a metal, the more readily it loses electrons.

Displacement Reaction

Displacement reactions involve a more electropositive metal kicking out a less electropositive metal from a compound.

Think of it as a more enthusiastic dancer stepping into the spotlight and pushing another dancer aside. This occurs because the eager dancer—our electropositive metal—can more effectively grab partners, or electrons, from the compound.

• The metal with higher electropositivity (like aluminum) can displace one with lower electropositivity (such as copper).
• However, if the metals are arranged the other way around, no displacement occurs, as the less electropositive metal can't outshine its counterpart.

If you put a copper spoon in aluminum nitrate, no displacement occurs, because copper is not electropositive enough to oust aluminum.

Metal Reactivity

Metal reactivity is closely linked to the electrochemical series and electropositivity.

A metal's reactivity can be thought of in terms of how easily it partakes in reactions, sacrificing its electrons to form new compounds.

• More reactive metals (like magnesium) tend to be more electropositive, losing electrons easily.
• The less reactive metals (like copper) hold onto their electrons more tightly.

Using our copper and aluminum example, copper is less reactive than aluminum, hence why the copper spoon doesn't cause any reaction in an aluminum nitrate solution.

Redox Reactions

Redox reactions, short for reduction-oxidation reactions, are processes where electrons are transferred between substances. These reactions are intrinsic to displacement reactions as well.

In such reactions:

• Oxidation refers to the loss of electrons.
• Reduction is the gain of electrons.

The concept of "OIL RIG" can help you remember this: "Oxidation Is Loss, Reduction Is Gain."

In our scenario with copper and aluminum nitrate, a redox reaction should have involved copper donating electrons (being oxidized) and aluminum accepting them (being reduced). However, this doesn't happen because copper can't displace aluminum due to lower electropositivity. Hence, the copper spoon remains unchanged.