Which one of the following statements is true when non-metals are dissolved in water?
They produce acidic oxides.
Understanding Non-metals and Their Reaction with Water
Let's analyze what happens when non-metals or their oxides interact with water. The behavior of non-metals when dissolved in water is primarily related to the nature of the oxides they form.
Nature of Non-metal Oxides
Non-metal oxides are generally acidic in nature. This means that when they dissolve in water, they typically form acidic solutions. Some non-metal oxides, however, are neutral, and a few can be amphoteric.
- Acidic Oxides: These are the most common type of non-metal oxides. Examples include sulfur dioxide (\(\text{SO}_2\)), carbon dioxide (\(\text{CO}_2\)), and nitrogen pentoxide (\(\text{N}_2\text{O}_5\)). When these dissolve in water, they react to form acids.
- Neutral Oxides: Some non-metals form oxides that do not react with water to form acids or bases. Examples include carbon monoxide (\(\text{CO}\)), nitric oxide (\(\text{NO}\)), and nitrous oxide (\(\text{N}_2\text{O}\)).
- Amphoteric Oxides: Very few non-metal oxides are amphoteric, meaning they can react with both acids and bases. For instance, some oxides of phosphorus can show amphoteric behavior.
Reaction of Acidic Oxides with Water
Acidic oxides dissolve in water to form corresponding acids. Here are a few examples:
- Carbon dioxide dissolving in water forms carbonic acid: \(\text{CO}_2\text{(g)} + \text{H}_2\text{O}\text{(l)} \rightarrow \text{H}_2\text{CO}_3\text{(aq)}\) Carbonic acid is a weak acid.
- Sulfur dioxide dissolving in water forms sulfurous acid: \(\text{SO}_2\text{(g)} + \text{H}_2\text{O}\text{(l)} \rightarrow \text{H}_2\text{SO}_3\text{(aq)}\) Sulfurous acid is an acid. Sulfur trioxide (\(\text{SO}_3\)) forms sulfuric acid: \(\text{SO}_3\text{(g)} + \text{H}_2\text{O}\text{(l)} \rightarrow \text{H}_2\text{SO}_4\text{(aq)}\) Sulfuric acid is a strong acid.
- Nitrogen pentoxide dissolving in water forms nitric acid: \(\text{N}_2\text{O}_5\text{(g)} + \text{H}_2\text{O}\text{(l)} \rightarrow 2\text{HNO}_3\text{(aq)}\) Nitric acid is a strong acid.
These reactions show that dissolving common non-metal oxides in water results in the formation of acidic solutions.
Analyzing the Options
Let's look at the given options in the context of our understanding:
They produce basic oxides.
This statement is generally incorrect for non-metals. Basic oxides are typically formed by metals (like \(\text{Na}_2\text{O}\), \(\text{CaO}\)). When metal oxides dissolve in water, they form bases (like \(\text{NaOH}\), \(\text{Ca(OH)}_2\)).
They produce acidic oxides.
Non-metals themselves don't produce oxides *when dissolved in water*. However, the oxides formed by non-metals (like \(\text{CO}_2\), \(\text{SO}_2\)) are acidic oxides, and when these oxides dissolve in water, they form acidic solutions. The option likely refers to the nature of the oxides formed by non-metals and their behavior in water. Considering the typical behavior discussed above, this statement aligns with the fact that non-metal oxides are acidic and make water acidic.
They produce neutral oxides.
While some non-metals do form neutral oxides (\(\text{CO}\), \(\text{NO}\)), it's not true for all or even most common non-metal oxides. The statement "They produce neutral oxides" as a general rule when dissolved in water is not accurate. The question likely refers to the typical or predominant behavior.
They provide hydroxides.
Hydroxides are typically formed when metal oxides or reactive metals react with water (e.g., \(\text{NaOH}\), \(\text{Ca(OH)}_2\)). While some non-metal compounds can form acidic hydroxides (like \(\text{H}_2\text{SO}_4\) can be thought of as a di-hydroxy compound, \((\text{HO})_2\text{SO}_2\)), the term "hydroxides" in contrast to acidic/basic oxides usually refers to bases formed by metals. Also, dissolving non-metals themselves directly in water doesn't always yield hydroxides in the same way metals do.
Based on the characteristic behavior of non-metal oxides reacting with water to form acids, the most accurate statement among the given options is that non-metal oxides are acidic oxides, leading to acidic solutions when dissolved in water.
| Property | Metals | Non-metals |
|---|---|---|
| Nature of Oxides | Basic (mostly) | Acidic (mostly), Neutral, Amphoteric |
| Reaction of Oxides with Water | Form bases (hydroxides) | Form acids (acidic solutions) |
| Example (Oxide + Water) | \(\text{Na}_2\text{O} + \text{H}_2\text{O} \rightarrow 2\text{NaOH}\) | \(\text{CO}_2 + \text{H}_2\text{O} \rightarrow \text{H}_2\text{CO}_3\) |
Therefore, the statement that aligns with the acidic nature of most non-metal oxides and their reaction with water is related to producing acidic oxides or forming acidic solutions.
Revision Table: Non-metals in Water
| Concept | Explanation | Typical Result in Water |
|---|---|---|
| Non-metal Oxides | Oxides formed by non-metals (e.g., \(\text{CO}_2\), \(\text{SO}_2\), \(\text{N}_2\text{O}_5\)) | Form acidic solutions when dissolved (e.g., carbonic acid, sulfurous acid, nitric acid). |
| Acidic Oxides | Oxides that react with water to form acids. | Lower the pH of water. |
| Basic Oxides | Oxides that react with water to form bases (usually metal oxides). | Raise the pH of water. |
| Neutral Oxides | Oxides that do not react with water to form acids or bases (e.g., \(\text{CO}\), \(\text{NO}\)). | Do not change the pH of water. |
Additional Information: Acid Rain and Non-metal Oxides
The concept of acidic non-metal oxides is very important in understanding environmental issues like acid rain. Pollutants like sulfur dioxide (\(\text{SO}_2\)) and nitrogen oxides (\(\text{NO}_\text{x}\)) are non-metal oxides released into the atmosphere from burning fossil fuels. These oxides dissolve in atmospheric moisture (water) to form sulfuric acid (\(\text{H}_2\text{SO}_4\)) and nitric acid (\(\text{HNO}_3\)), which then fall to the Earth as acid rain. This demonstrates the acidic nature of non-metal oxides and their ability to form acidic solutions when in contact with water.
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