Problem 73 - Introductory Chemistry Atoms First

Question

Suppose you have two ionic compounds, A and B. The only significant difference between them is that the ionic bonds that hold the lattice together in compound \(\mathrm{A}\) are stronger than those in compound B. Which compound would you expect to be more soluble in water? Explain your answer.

Step-by-Step Solution

Answer

Compound B is expected to be more soluble in water than compound A. This is because compound B has weaker ionic bonds, which require less energy to break and allow the compound to dissolve more easily in water.

Step 1: Understand the Relationship between Bond Strength and Solubility

When an ionic compound dissolves in water, the ions are separated due to the attractions between the charged particles of the compound and the water molecules. The solubility of an ionic compound in water is dependent on the balance between the forces holding the ions together and the attractions between the ions and water molecules. A strong ionic bond means that more energy is needed to break the bond and dissolve the compound in water, while a weak bond would require less energy to dissolve the compound.

Step 2: Compare the Strength of the Ionic Bonds

In our case, compound A has stronger ionic bonds holding the lattice together than compound B. This means that more energy would be required to break the bonds in compound A than in compound B.

Step 3: Determine Solubility Based on Bond Strength

Since the ionic bonds in compound A are stronger than those in compound B, it would require more energy to dissolve compound A in water. Consequently, compound B, which has weaker ionic bonds, would require less energy to dissolve and therefore is more soluble in water.

Step 4: Conclusion:

Compound B is expected to be more soluble in water than compound A due to its weaker ionic bonds, which would require less energy to break and allow the compound to dissolve more easily.

Key Concepts

Ionic Bonds

Ionic bonds form when one atom donates an electron to another atom, resulting in positively and negatively charged ions that attract each other. This bond is common in compounds formed between metals and non-metals. The strength of these bonds depends not only on the charge of the ions involved but also on the distance between them.
More charge and shorter distances lead to stronger ionic bonds. These bonds are key in determining the properties of ionic compounds, like high melting and boiling points.

• Formed by electron transfer.
• Result in attraction between oppositely charged ions.
• Affect compound properties like hardness and electrical conductivity.

Understanding these bonds is essential to predicting behaviors of different substances, especially when they dissolve in water.

Lattice Energy

Lattice energy is the energy required to separate a mole of an ionic solid into gaseous ions. It is a measure of the strength of the forces between the ions in an ionic solid. The greater the lattice energy, the stronger the forces holding the ions together.
Factors influencing lattice energy include the size of the ions and their charges. Smaller and more highly charged ions result in higher lattice energies.

• High lattice energy indicates strong ionic bonds.
• Reflects the stability of an ionic compound.
• Inversely related to solubility in water.

Knowing about lattice energy helps understand why some compounds remain solid under conditions where others dissolve.

Solubility

Solubility refers to the maximum amount of a substance that can dissolve in a given quantity of solvent at a specific temperature. It depends on the nature of the compound and the solvent used.
For ionic compounds, solubility is greatly influenced by the bond strength within the compound and the attraction between the ions and the solvent molecules.

• Measured in terms of concentration.
• Affected by temperature and pressure.
• Related to the strength of ionic bonds.

Understanding solubility helps predict how substances behave in different environments, which is particularly useful in chemical reactions and industrial applications.

Bond Strength

Bond strength in ionic compounds is determined by the forces pulling the ions together. Stronger bonds mean a compound is less likely to dissolve easily in water. There are several factors affecting bond strength, such as the size and charge of the ions involved.
Greater charges and smaller ionic radii contribute to stronger ionic bonds.

• Influences solubility and melting points.
• Determined by electrostatic forces between ions.
• Stronger bonds require more energy to break.

Knowing about bond strength allows predictions about a compound's physical properties, like its solubility in different solvents.

Water Solubility

Water solubility is the ability of a substance to dissolve in water. This property is crucial for many chemical reactions and biological processes. Water is a polar molecule, meaning it has a partial positive and negative charge, which allows it to interact effectively with other polar substances, like ions in ionic compounds.
When an ionic compound dissolves, these interactions replace the ionic bonds, leading the compound to disperse in water.

• Depends on interaction between water molecules and ions.
• Stronger ionic bonds reduce solubility.
• Highly related to lattice energy and bond strength.

Understanding water solubility is important for chemistry experiments and in designing pharmaceuticals, as it affects how substances are absorbed and transported in the body.