Understanding Metal Reactivity with Water

The reactivity series of metals is a list of metals arranged in order of their decreasing reactivity. A metal's reactivity can be determined by how easily it loses electrons and forms positive ions. One way to observe and compare the reactivity of metals is by their reaction with water, which can vary depending on the temperature of the water (cold water, hot water, or steam).

Different metals react with water differently:

• Highly reactive metals (like potassium, sodium, calcium) react vigorously with cold water.
• Moderately reactive metals (like magnesium, aluminium, zinc, iron) react with hot water or steam.
• Less reactive metals (like lead, copper, silver, gold) do not react with water or steam under normal conditions.

Analyzing the Reactivity of Given Metals with Water

Let's consider the reactivity of the specific metals given in the options: Zinc (Zn), Iron (Fe), Lead (Pb), and Copper (Cu).

• Zinc (Zn): Zinc reacts with steam to form zinc oxide and hydrogen gas. This reaction is slower than that of more reactive metals with cold water. The equation is typically represented as: \(\text{Zn(s)} + \text{H}_2\text{O(g)} \rightarrow \text{ZnO(s)} + \text{H}_2\text{g)}\)
• Iron (Fe): Iron also reacts with steam, though even more slowly than zinc, to form iron(II,III) oxide (magnetite) and hydrogen gas. The reaction requires prolonged heating of iron in steam. The equation is: \(3\text{Fe(s)} + 4\text{H}_2\text{O(g)} \rightarrow \text{Fe}_3\text{O}_4\text{(s)} + 4\text{H}_2\text{g)}\)
• Lead (Pb): Lead's reaction with water is very limited. While sometimes listed as reacting slowly with hot water or steam, its reactivity is considerably less than that of zinc and iron with steam. Lead quickly gets coated with a layer of lead oxide or lead carbonate in air and water, which protects it from further reaction. For practical purposes in comparing with Zn and Fe's reaction with steam, Lead's reactivity with water is much lower.
• Copper (Cu): Copper does not react with water or steam under normal conditions. This is why copper pipes are widely used for plumbing.

Determining the Correct Reactivity Order

Based on the reactivity with water (specifically steam for these metals), we can arrange them in decreasing order of reactivity:

• Zinc reacts with steam.
• Iron reacts with steam, but generally slower than zinc.
• Lead reacts very slowly with hot water/steam, much less readily than iron and zinc with steam.
• Copper does not react with water/steam.

Therefore, the order of decreasing reactivity with water is Zinc > Iron > Lead > Copper.

Summary Table of Reactivity with Water

Comparing the reactivity, Zinc is more reactive with steam than Iron, which is more reactive than Lead with hot water/steam, and Copper shows no reaction. This establishes the correct reactivity series with water among these metals as Zinc > Iron > Lead > Copper.

Revision Table: Reactivity Series Key Points

Additional Information on Metal Reactivity

The position of a metal in the reactivity series is determined by various factors, including its enthalpy of atomisation, ionization energy, and hydration energy of its ions. Metals higher in the series have a greater tendency to lose electrons and are stronger reducing agents.

The reactivity series is useful for predicting the outcome of displacement reactions. A more reactive metal can displace a less reactive metal from its salt solution or oxide.

For example, Zinc is above Iron in the reactivity series, so Zinc can displace Iron from Iron(II) sulfate solution:

\(\text{Zn(s)} + \text{FeSO}_4\text{(aq)} \rightarrow \text{ZnSO}_4\text{(aq)} + \text{Fe(s)}\)

However, Copper is below Iron, so Copper cannot displace Iron from Iron(II) sulfate solution.

Understanding the reactivity series helps in various chemical processes, including extraction of metals, preventing corrosion, and designing experiments involving metal reactions.