To evaluate the statements regarding dissolution rates:
I. Stirring slows down (decreases) the rate of dissolution.
This statement is false. Stirring generally increases the rate of dissolution because it helps to distribute solute particles more evenly and allows fresh solvent to come into contact with the solute.
II. Grinding solids increases their surface area of contact.
This statement is true. Grinding solid materials reduces their particle size, which increases the surface area available for interaction with the solvent, enhancing the rate of dissolution.
III. Heating slows down (decreases) the rate of dissolution.
This statement is false. Heating typically increases the rate of dissolution for most solids in liquids because it increases the kinetic energy of molecules, allowing them to interact more effectively.
IV. Grinding solids speeds up their rate of dissolution.
This statement is true. As previously mentioned, by increasing the surface area of the solid, grinding enhances the interaction with the solvent, thereby increasing the rate of dissolution.
Based on the evaluations:
- Statement II is true.
- Statement IV is true.
- Statements I and III are false.
Therefore, the correct responses are: B II and IV