Imagine you have two mysterious materials, X and Y. When you try to press material X, it feels rigid and does not change its shape easily. On the other hand, material Y easily changes its shape when you press it. Now, when you mix both materials in water, only material X dissolves completely, while material Y remains unchanged. What can materials X and Y be? Can you identify whether material X is hard or soft? What about material Y? Justify your answer.
Material X is hard and soluble. Material Y is soft and insoluble.
Material X feels rigid and does not change its shape easily when pressed, which indicates it is a hard material. Hard materials are difficult to compress or scratch.
Material X also dissolves completely in water, making it soluble. Examples of such materials include salt or sugar crystals, which are hard to compress but dissolve in water.
Material Y easily changes its shape when pressed, indicating it is a soft material. Soft materials can be compressed or scratched easily.
Material Y remains unchanged in water, meaning it is insoluble. Examples include rubber, sponge, or wax, which are soft and do not dissolve in water.
The properties of hardness/softness and solubility/insolubility are independent of each other, so a material can be hard and soluble (like salt) or soft and insoluble (like wax).
Explanation
The chapter defines hard materials on Page 7 as those which are difficult to compress or scratch, while soft materials can be easily compressed. On Pages 10-11, soluble materials are described as those that disappear when mixed in water, while insoluble materials do not mix with water and remain unchanged. This question combines both properties to test understanding of material characteristics.
Solution Steps
Material X is identified as hard and soluble, while Material Y is identified as soft and insoluble.
Material X is hard because it feels rigid and resists shape change, meaning it is difficult to compress or scratch.
Material X is soluble because it dissolves completely in water, similar to salt or sugar crystals.
Material Y is soft because it easily changes shape when pressed, meaning it can be compressed or scratched easily.
Material Y is insoluble because it remains unchanged in water, similar to rubber, sponge, or wax.
The properties of hardness/softness and solubility/insolubility are independent of each other.