Question

Many ionic crystals dissolve in water because (1) water is an amphiprotic solvent (2) water is a high boiling liquid (3) the process is accompanied by a positive heat of solution (4) Water decreases the interionic attraction in the crystal lattice due to solvation

Short answer

Water decreases interionic attraction due to solvation, making ionic crystals dissolve in water.

Step-by-step solution

Understand the nature of water

Water is a polar solvent, meaning it has a partial positive charge on one side and a partial negative charge on the other side. This property makes it very effective at dissolving ionic compounds.

Review the solvation process

When an ionic crystal dissolves in water, the water molecules surround the ions of the crystal. This is known as solvation or hydration. The partial positive charge of the water molecules will surround the negative ions, and the partial negative charge of the water molecules will surround the positive ions.

Analyze the interionic attraction

The attraction between the water molecules and the ions in the crystal reduces the interionic attraction within the crystal lattice. This reduction in attraction allows the ions to separate and dissolve more easily in the water.

Relate to the given options

Among the given options, option (4) 'Water decreases the interionic attraction in the crystal lattice due to solvation' is the most accurate. The solvation process effectively decreases the forces holding the crystal lattice together, causing it to dissolve.

Key concepts

Polar Solvents

Understanding why polar solvents like water can dissolve ionic compounds begins with their structure. Water is a polar molecule, meaning it has a partial positive charge on one side and a partial negative charge on the other. This polarity arises because of the difference in electronegativity between hydrogen and oxygen atoms. In a water molecule, oxygen is more electronegative and pulls the electrons towards itself, creating a dipole. The oxygen end becomes slightly negative while the hydrogen ends become slightly positive. This dipolar nature allows water to interact with and surround ionic substances.

• Polarity is essential for the dissolving process.
• Water's partial charges enable interactions with ionic compounds.

Polar solvents are crucial for various chemical reactions and dissolving processes because they can stabilize different ions, thus breaking down crystal lattices of ionic compounds more effectively.

Solvation Process

The solvation process, or hydration when water is involved, is a critical step in dissolving ionic crystals. When ionic substances such as salts dissolve in water, the water molecules surround the individual ions. This is how the solvation process works:

1. The ions in the crystal are attracted to the polar water molecules.
2. The partial positive charges on the hydrogen atoms of water surround the negative ions (anions).
3. The partial negative charges on the oxygen atoms of water surround the positive ions (cations).
By surrounding and stabilizing these ions, water breaks the ionic bonds holding the crystal lattice together. This allows the ions to disperse evenly throughout the solution.

• Hydration involves the surrounding of ions by water molecules.
• Intermolecular forces play a significant role in this process.

The efficiency of the solvation process depends on the strength of interactions between water molecules and the ions.

Interionic Attraction

Interionic attraction refers to the forces holding the ions together in an ionic crystal lattice. When an ionic compound dissolves in water, these interionic forces must be overcome. Here is why water is effective in decreasing interionic attraction:

1. The polarity of water creates a strong interaction with the ions in the crystal.
2. The solvation process disrupts the electrostatic forces between the ions.
3. When water molecules surround and stabilize individual ions, the ions can move freely apart.
This reduction in interionic attraction is crucial for dissolving the crystal lattice, making the process more efficient:

• Ionic bonds in the crystal are broken by strong interactions with water molecules.
• This makes the ions separate and dissolve in the solution.

Water's ability to decrease interionic attraction plays a pivotal role in making it an excellent solvent for ionic compounds. By understanding how polar solvents and solvation processes work, one can appreciate the reasons behind the dissolution of ionic crystals in water.