Chemistry of Dissolving Table Salt in Water

What happens when sodium chloride (NaCl) dissolves in water?

• It remains solid.

• It forms a new substance.

• It reacts and releases bubbles.

• It breaks into sodium and chloride ions.

Answer explanation

When sodium chloride (NaCl) dissolves in water, it dissociates into sodium (Na+) and chloride (Cl-) ions. This process does not form a new substance or release bubbles, making the correct answer the dissociation into ions.

Which type of interaction stabilizes Na⁺ and Cl⁻ in water?

• Covalent forces.

• Dispersion forces.

• Hydrogen bonding between water.

• Ion-dipole attractions with water molecules.

Answer explanation

Ion-dipole attractions occur when the charged ions (Na⁺ and Cl⁻) interact with the polar water molecules, stabilizing them in solution. This is the primary interaction that keeps the ions dissolved in water.

What energy change happens when NaCl’s bonds break?

• No energy change.

• Energy stays the same.

• Heat is released into the solution.

• Heat is absorbed from the surroundings.

Answer explanation

When NaCl's bonds break, energy is required to overcome the ionic attractions, leading to heat being absorbed from the surroundings. This endothermic process results in a temperature drop in the solution.

What is the total energy change when NaCl dissolves?

• No energy is involved.

• The process is unpredictable.

• Heat is given off, making it exothermic.

• Heat is absorbed, making it endothermic.

Answer explanation

When NaCl dissolves in water, it absorbs heat from the surroundings, resulting in a decrease in temperature. This process is endothermic, as it requires energy input to break the ionic bonds and separate the ions.

Why does NaCl dissolve if breaking bonds needs energy?

• A) Water splits apart.

• B) The process is automatic.

• C) Hydration energy counteracts it.

• D) NaCl does not dissolve in water.

Answer explanation

NaCl dissolves in water because the energy released during hydration (when water molecules surround and stabilize the ions) is greater than the energy required to break the ionic bonds, making the process energetically favorable.

Which best explains the role of water in dissolving NaCl?

• A) Water forms a solid.

• B) Water reacts with NaCl.

• C) It stabilizes the Na⁺ and Cl⁻ ions.

• D) It breaks down into smaller molecules.

Answer explanation

Water stabilizes the Na⁺ and Cl⁻ ions by surrounding them with its polar molecules, effectively separating and dissolving the salt. This is why option C is the correct explanation for the role of water in dissolving NaCl.

Which statement correctly describes NaCl dissolution?

• NaCl remains solid.

• It only releases heat.

• Lattice bonds break apart.

• Lattice bonds break, and hydration occurs.

Answer explanation

When NaCl dissolves, the ionic lattice breaks apart due to the interaction with water molecules, leading to hydration. This process involves both breaking lattice bonds and surrounding the ions with water, making the correct choice 'Lattice bonds break, and hydration occurs.'

What does NaCl's endothermic dissolution suggest?

• No connection exists.

• Hydration is much stronger.

• Both forces are balanced.

• Lattice forces are stronger than hydration.

Answer explanation

NaCl's endothermic dissolution indicates that the energy required to break the lattice forces is greater than the energy released during hydration, suggesting that lattice forces are indeed stronger than hydration.

How would weaker dipoles in water affect NaCl?

• NaCl dissolves faster.

• Lattice bonds weaken.

• Heat release increases.

• The dissolution happens less easily.

Answer explanation

Weaker dipoles in water reduce its ability to stabilize the ions from NaCl, making it harder for the salt to dissolve. Thus, the dissolution happens less easily.

How can a student test if dissolving NaCl is endothermic?

• Observe color changes.

• Measure water volume.

• Check for solid formation.

• Measure solution temperature before and after.

Answer explanation

To determine if dissolving NaCl is endothermic, measure the solution's temperature before and after dissolving. A decrease in temperature indicates that the process absorbs heat, confirming it is endothermic.