The friction generates heat which converts red phosphorus to white phosphorus.
Explanation
The mechanism of a safety matchstick relies on a chemical reaction initiated by friction. The reactive components are separated between the matchstick head and the striking surface to ensure safety and prevent accidental ignition.
Mechanism of Action:
- Composition: The head of the safety matchstick typically contains potassium chlorate (an oxidizing agent) and antimony trisulfide (fuel), along with glue. The striking surface on the box contains powdered glass (for friction) and red phosphorus.
- Reaction Process: When the matchstick is rubbed against the striking surface, the friction generates heat. This heat converts a small amount of red phosphorus into white phosphorus.
- Ignition: White phosphorus is highly unstable and reacts immediately with the potassium chlorate on the match head. This reaction produces enough heat to ignite the antimony trisulfide, which subsequently sustains the combustion of the wood.
Analysis of Options:
- The friction generates heat which converts red phosphorus to white phosphorus. is correct: It accurately identifies the initiating step: the conversion of red phosphorus to white phosphorus due to frictional heat.
- The friction directly ignites the potassium chlorate. is incorrect: Potassium chlorate does not ignite directly from friction; it requires the heat from the phosphorus reaction to decompose and release oxygen.
- The sandpaper on the box creates a spark that lights the wood. is incorrect: The process is a specific chemical chain reaction, not merely a mechanical spark lighting the wood.
- The chemicals on the matchstick react with oxygen in the air spontaneously. is incorrect: Safety matches are designed specifically not to react spontaneously with air; they require the specific interaction with the striking surface.
Key Takeaway:
The ignition of a safety match is triggered when frictional heat converts Red Phosphorus (on the strip) into highly reactive White Phosphorus, which then reacts with Potassium Chlorate.