Which of the following metals does not react with air?
Gold, Platinum
Metal Reactivity: Which Metals Do Not React with Air?
Understanding how metals react with air is a key concept in chemistry, specifically related to the reactivity series of metals. Metals are classified based on their tendency to lose electrons and undergo chemical reactions. Air primarily contains oxygen, nitrogen, argon, and small amounts of other gases like carbon dioxide and water vapour. The reaction of metals with air usually refers to their reaction with oxygen.
Highly reactive metals react quickly and sometimes violently with oxygen in the air, even at room temperature. Less reactive metals might react slowly, often requiring heating, while some very unreactive metals do not react with air at all under normal conditions.
Analyzing the Reactivity of Given Metals
Let's look at the reactivity of the metals mentioned in the options:
- Potassium (K): Potassium is a highly reactive alkali metal. It reacts vigorously and exothermically with oxygen in the air, tarnishing rapidly and potentially catching fire.
- Nickel (Ni): Nickel is moderately reactive. It reacts slowly with oxygen in moist air, forming a protective oxide layer on its surface (passivation) which prevents further reaction. However, it does react.
- Silver (Ag): Silver is relatively unreactive compared to alkali metals or transition metals like nickel. It does not react directly with oxygen in dry air. However, it reacts with sulfur compounds (like hydrogen sulfide) present in the air, causing it to tarnish and turn black (forming silver sulfide). So, while it doesn't react significantly with oxygen, it does react with other components of polluted air.
- Gold (Au): Gold is a very unreactive noble metal. It is located very low in the reactivity series. Gold does not react with oxygen, moisture, or most acids and alkalis in the air under normal conditions.
- Platinum (Pt): Platinum is also a very unreactive noble metal, similar to gold. It is even less reactive than gold. Platinum does not react with oxygen or other components of air under normal conditions.
Evaluating the Options
We are looking for a pair of metals that do not react with air.
- Option 1: Gold, Platinum - Both Gold and Platinum are noble metals and are known for their extreme unreactivity with air (oxygen, moisture) under normal conditions.
- Option 2: Silver, Platinum - Platinum does not react with air. However, Silver reacts with sulfur compounds in the air, leading to tarnishing. While it doesn't react readily with oxygen, it is affected by air components.
- Option 3: Potassium, Nickel - Potassium is highly reactive and reacts violently with air. Nickel is moderately reactive and reacts slowly with air, forming an oxide layer. Neither of these metals fits the criteria of *not* reacting with air.
- Option 4: Gold, Silver - Gold does not react with air. However, Silver reacts with sulfur compounds in the air (tarnishing).
Based on the reactivity analysis, the pair of metals that are most unreactive and do not react with air under normal conditions are Gold and Platinum.
| Metal | Reactivity with Air (Oxygen) | Notes |
|---|---|---|
| Potassium | Reacts vigorously/violently | Highly reactive |
| Nickel | Reacts slowly | Forms protective oxide layer |
| Silver | Does not react readily with oxygen, but tarnishes | Reacts with sulfur compounds in air |
| Gold | Does not react | Very unreactive noble metal |
| Platinum | Does not react | Very unreactive noble metal |
Conclusion on Metals and Air Reactivity
The metals Gold and Platinum are classified as noble metals due to their very low reactivity. They resist corrosion and oxidation in air and moisture, making them valuable for jewellery, coins, and industrial applications where stability is required. Other metals like Potassium and Nickel are more reactive, and even Silver shows some reaction with air components (sulfur compounds), leading to tarnishing.
Therefore, the pair of metals that does not react with air among the given options is Gold and Platinum.
Revision Table: Metal Reactivity Concepts
| Concept | Explanation |
|---|---|
| Reactivity Series | An arrangement of metals in decreasing order of their reactivity. More reactive metals are at the top. |
| Reaction with Air | Usually refers to reaction with oxygen. Can also involve moisture or other gases in air. |
| Noble Metals | Metals with very low reactivity, such as Gold, Platinum, Palladium, etc. They resist oxidation and corrosion. |
| Tarnishing | A form of corrosion that dulls or darkens the surface of a metal. For silver, it's often due to reaction with sulfur. |
Additional Information: Reactivity Series & Noble Metals
The reactivity series helps predict whether a metal will react with substances like water, acids, or oxygen in the air. Metals higher in the series displace metals lower in the series from their compounds. Potassium is at the very top of the series, making it highly reactive. Nickel is somewhere in the middle. Silver, Gold, and Platinum are at the very bottom of the series, indicating very low reactivity.
The noble metals (Gold, Platinum, Palladium, Rhodium, Iridium, Ruthenium) are known for their exceptional resistance to chemical attack. This property is why they are used in conditions where other metals would corrode or degrade. Their inertness to reaction with air is a key characteristic.
Important Questions from Metals
Which of the following is NOT an alloy?
Why are aluminum items such as pressure cookers, saucepans, etc. anodized?
A. To increase their conductivity.
B. To increase their tensile strength.
C. To prevent them from rusting.
D. To make them lighter and shinier.
Which of the following statements is INCORRECT?
Which of the following is combined to form Solder?
Gold is mixed with copper ______.
