Question

IIydrogen gas will not reduce (1) heated cupric oxide (2) heated ferric oxide (3) heated stannic oxide (4) heated aluminiun oxidc

Short answer

Hydrogen gas will not reduce heated aluminum oxide (Al2O3).

Step-by-step solution

Understanding Reduction by Hydrogen Gas

Hydrogen gas can reduce metal oxides that are less reactive than hydrogen itself in the reactivity series. Metals that are more reactive than hydrogen cannot be reduced by hydrogen gas.

Identify the Metal Oxides and Their Reactivity

List the given metal oxides: CuO (cupric oxide), Fe2O3 (ferric oxide), SnO2 (stannic oxide), Al2O3 (aluminum oxide). Determine their positions relative to hydrogen in the reactivity series: Copper (less reactive), Iron (slightly more reactive), Tin (similar reactivity), Aluminum (more reactive).

Analyze Reactivity with Hydrogen

Hydrogen can reduce metal oxides less reactive than itself. Cupric oxide (CuO) and stannic oxide (SnO2) can be reduced because copper and tin are less reactive or have similar reactivity to hydrogen. Ferric oxide (Fe2O3) can be reduced because iron is slightly more reactive.

Determine Which Oxide Cannot be Reduced

Since aluminum is significantly more reactive than hydrogen, hydrogen gas will not be able to reduce aluminum oxide (Al2O3).

Key concepts

Metal Oxides

Metal oxides are compounds composed of metal atoms combined with oxygen atoms. They form through the direct reaction of a metal with oxygen or other oxidizing agents. Typically, metal oxides have ionic bonds due to the transfer of electrons from the metal to the oxygen. Examples of metal oxides include CuO (cupric oxide), Fe2O3 (ferric oxide), SnO2 (stannic oxide), and Al2O3 (aluminum oxide). Each of these oxides is created when their respective metals react with oxygen, leading to different properties and reactivity levels based on the nature of the metal involved.

Reactivity Series

The reactivity series is an arrangement of metals in order of their reactivity from highest to lowest. It is crucial for understanding various chemical reactions, especially those involving reductions and oxidations. In the reactivity series, metals like potassium, sodium, and calcium are at the top, meaning they are highly reactive. Metals such as gold and platinum are at the bottom, indicating they are least reactive. Hydrogen is included in the series for comparison, and any metal above hydrogen is more reactive, while metals below are less reactive. For instance, aluminum is above hydrogen, making it more reactive, while copper and tin are below it, making them less reactive or similarly reactive.

Chemical Reduction

Chemical reduction involves the gain of electrons by a substance. In the context of reducing metal oxides using hydrogen gas, this process entails hydrogen gas acting as a reducing agent that donates electrons to the metal oxide. This reaction turns the metal oxide into the pure metal and forms water or another compound with the oxygen that was part of the original oxide.
For example, when hydrogen gas reduces cupric oxide:$$\text{CuO}+{\text{H}}_2\to \text{Cu}+{\text{H}}_2\text{O}$$In this reaction, hydrogen gas reduces CuO to copper metal and water. Similarly, hydrogen can reduce SnO2 to tin under suitable conditions. However, since aluminum is much more reactive than hydrogen, it cannot reduce Al2O3. Instead, hydrogen is used effectively to reduce oxides of metals that are less reactive than or similarly reactive to hydrogen itself.