Question

Identify the correct order of acidic strengths of \(\mathrm{CO}_{2}\), \(\mathrm{CuO}, \mathrm{CaO}\) and \(\mathrm{H}_{2} \mathrm{O}\) (a) \(\mathrm{CaO}<\mathrm{CuO}<\mathrm{H}_{2} \mathrm{O}<\mathrm{CO}_{2}\) (b) \(\mathrm{H}_{2} \mathrm{O}<\mathrm{CuO}<\mathrm{CaO}<\mathrm{CO}_{2}\) (c) \(\mathrm{CaO}<\mathrm{H}_{2} \mathrm{O}<\mathrm{CuO}<\mathrm{CO}_{2}\) (d) \(\mathrm{H}_{2} \mathrm{O}<\mathrm{CO}_{2}<\mathrm{CaO}<\mathrm{CuO}\)

Short answer

The correct order of acidic strengths is (a) \( \text{CaO} < \text{CuO} < \text{H}_2 \text{O} < \text{CO}_2 \).

Step-by-step solution

Categorize oxides based on acidic or basic nature

First, identify each substance as a basic or acidic oxide. \( \text{CO}_2 \) is a non-metal oxide and is acidic. \( \text{CuO} \) is a metal oxide of a transition metal and weakly acidic in nature. \( \text{CaO} \) is a basic oxide, as it is an oxide of an alkaline earth metal. \( \text{H}_2\text{O} \) is neutral but can act as a weak acid or base depending on the context.

Determine relative acidity

Rank the substances based on their acidity. \( \text{CO}_2 \) is clearly acidic, while \( \text{CuO} \) is less acidic than \( \text{CO}_2 \) due to its metallic nature. \( \text{H}_2\text{O} \) is generally neutral and less acidic than \( \text{CO}_2 \) and \( \text{CuO} \). \( \text{CaO} \), being a basic oxide, ranks lowest in acidity.

Match with given options

Compare the determined order to the provided options: \( \text{CaO} < \text{CuO} < \text{H}_2\text{O} < \text{CO}_2 \) (option a). \( \text{H}_2\text{O} < \text{CuO} < \text{CaO} < \text{CO}_2 \) (option b). \( \text{CaO} < \text{H}_2\text{O} < \text{CuO} < \text{CO}_2 \) (option c). \( \text{H}_2\text{O} < \text{CO}_2 < \text{CaO} < \text{CuO} \) (option d). The correct order based on acidity is option (a): \( \text{CaO}<\text{CuO}<\text{H}_2 \text{O}<\text{CO}_2 \).

Key concepts

Acidic Oxides

Acidic oxides are usually formed from non-metals and exhibit acidic properties when they react with water. An excellent example of an acidic oxide is carbon dioxide (\(\text{CO}_2\)). When carbon dioxide reacts with water, it forms carbonic acid (\(\text{H}_2\text{CO}_3\)), which is a weak acid. These oxides tend to lower the pH of a solution, making it more acidic.

• Typically derived from non-metal elements.
• React with water to form acids.
• Increase the acidity of solutions.

Understanding the role and behavior of acidic oxides helps explain the acidity order among compounds like \(\text{CO}_2\), \(\text{CuO}\), \(\text{CaO}\), and \(\text{H}_2\text{O}\).
Knowing that \(\text{CO}_2\) is more acidic than the rest is crucial for correctly determining the order of acidic strength.

Basic Oxides

Basic oxides are primarily formed from metals, particularly alkali and alkaline earth metals. A typical basic oxide is calcium oxide (\(\text{CaO}\)), which reacts with water to form a strong base, namely calcium hydroxide (\(\text{Ca(OH)}_2\)).

• Generally come from metals.
• React with water to produce bases.
• Used to neutralize acidic environments.

Basic oxides such as \(\text{CaO}\) lower acidity and are less acidic than non-metal oxides like \(\text{CO}_2\). This characteristic makes them vital in joining the acidity order among the given compounds, with \(\text{CaO}\) having the least acidic nature.

Neutral Substances

Water (\(\text{H}_2\text{O}\)) is often considered a neutral substance. However, its neutrality can shift under specific conditions since it can act as either a weak acid or a weak base. This dual nature is due to the amphoteric behavior of water.

• Usually neutral, but can be amphoteric.
• Acts as a weak acid or base in various reactions.
• Vital part of understanding acidity in chemistry.

In the context of acidic strength, \(\text{H}_2\text{O}\) plays a transitional role, placing it between basic oxides like \(\text{CaO}\) and more acidic substances like \(\text{CO}_2\). This feature ensures water is a less acidic choice in many scenarios.

Chemical Properties

Understanding the chemical properties of different oxides is crucial for determining their behavior and interactions in reactions. Properties such as acidity, basicity, and neutrality rely on the inherent characteristics shaped by the atomic structure and electron configurations of the atoms involved.

• Acidity is dominated by non-metal oxides.
• Basicity is generally due to metal oxides.
• Neutral or amphoteric behavior is seen in substances like water.

These chemical properties define the order of acidity strength across various substances. They assist with predicting the outcomes of chemical reactions involving oxides, like determining the correct acidity sequence among compounds such as \(\text{CO}_2\), \(\text{CaO}\), and others.

Transition Metal Oxides

Transition metal oxides, such as copper(II) oxide (\(\text{CuO}\)), exhibit diverse chemical behaviors due to their unique electron structures. They can possess varying degrees of acidity and basicity, often acting neither as strong acids nor strong bases.

• Contain transition metals with d-electrons.
• Exhibit both acidic and basic properties, often weakly.
• Flexible in reactions compared to strictly acidic or basic oxides.

Copper(II) oxide (\(\text{CuO}\)) is notably less acidic than non-metallic oxides like \(\text{CO}_2\) but more so than basic oxides such as \(\text{CaO}\). This nuanced positioning helps refine the acidic strength order among the compounds evaluated.