Question

For food storage, what is the advantage of placing a metal lid on a glass jar? (Hint: Why does running the metal lid under hot water for a minute help you open such a jar?)

Short answer

Question: Explain the advantage of using a metal lid on a glass jar for food storage and how running the metal lid under hot water can help open the jar. Answer: The advantage of using a metal lid on a glass jar for food storage is that it creates an airtight seal due to the higher rate of thermal expansion of metals, preventing the entry of air, contaminants, and microorganisms. Running the metal lid under hot water causes it to heat up and expand more than the glass, loosening the airtight seal and making it easier to open the jar.

Step-by-step solution

Identifying the materials and their properties

First, we need to identify the materials involved in this exercise: a metal lid and a glass jar. Metals generally have a higher rate of thermal expansion compared to glass. This means that metals expand more when heated and contract more when cooled compared to glass.

Understanding the advantage of a metal lid on a glass jar

Due to the higher rate of thermal expansion of metals, placing a metal lid on a glass jar creates an airtight seal as the metal lid contracts around the glass jar's opening when it cools down. This advantage prevents the entry of air, microorganisms, and any other contaminants, thus ensuring the food inside the jar is well-preserved.

Explaining the link between heating the metal lid and opening the jar

When the metal lid is placed under hot water, it heats up and expands. Since the metal expands more than the glass, loosening the airtight seal between the lid and the jar. This process makes it easier to open the jar, as it reduces the force required to break the seal between the lid and the jar.

Conclusion

In conclusion, the advantage of using a metal lid on a glass jar for food storage is the ability to create an airtight seal, which preserves the food inside by preventing the entry of contaminants. Running the metal lid under hot water helps to open the jar, as the expansion of the metal due to heating breaks the tight seal, thus making it easier to open.