If a single 5-g block of NaCl is placed in water, it dissolves slowly, but if 5 g of powdered NaCl is placed in water, it dis- solves rapidly. Explain.

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Understand the concept of surface area and its effect on the rate of dissolution. The rate at which a solute dissolves in a solvent is influenced by the surface area of the solute exposed to the solvent.

Recognize the difference in surface area between a single block of NaCl and powdered NaCl. A single block has a relatively smaller surface area exposed to the water compared to the same mass of NaCl in powdered form.

Relate the increased surface area of the powdered NaCl to the rate of dissolution. With more surface area exposed, there are more opportunities for the water molecules to interact with the NaCl particles.

Consider the process of dissolution at the molecular level. Water molecules must collide with the NaCl lattice to break the ionic bonds and disperse the ions throughout the solution.

Conclude that powdered NaCl dissolves faster than a block of NaCl because the increased surface area of the powder results in more frequent and effective collisions between water molecules and NaCl particles, leading to a quicker breakdown of the ionic lattice.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Solubility

Solubility refers to the ability of a substance to dissolve in a solvent, forming a homogeneous solution. In the case of NaCl, its solubility in water is influenced by factors such as temperature and the surface area of the solute. A larger surface area allows for more interactions between the solute and solvent molecules, leading to faster dissolution.

Surface Area

Surface area is the total area of the surface of a three-dimensional object. When a solid solute like NaCl is powdered, its surface area increases significantly compared to a solid block. This increased surface area allows more water molecules to interact with the NaCl particles simultaneously, facilitating a quicker dissolution process.

Dissolution Process

The dissolution process involves the breaking of ionic bonds in a solute and the surrounding of solute particles by solvent molecules. For NaCl, water molecules, which are polar, surround the Na+ and Cl- ions, pulling them apart and allowing them to disperse in the solution. The rate of this process is affected by the physical form of the solute, with powdered forms dissolving faster due to their increased exposure to the solvent.

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