Problem 15 - Chemistry: The Central Science in SI Units, Global Edition

Question

We have learned in this chapter that many ionic solids dissolve in water as strong electrolytes; that is, as separated ions in solution. Which statement is most correct about this process? (a) Water is a strong acid and therefore is good at dissolving ionic solids. (b) Water is good at solvating ions because the hydrogen and oxygen atoms in water molecules bear partial charges. (c) The hydrogen and oxygen bonds of water are easily broken by ionic solids.

Step-by-Step Solution

Answer

The most correct statement about the process of many ionic solids dissolving in water as strong electrolytes is (b) Water is good at solvating ions because the hydrogen and oxygen atoms in water molecules bear partial charges. This allows water molecules to surround and stabilize dissolved ions, forming hydration shells around them. This process is known as solvation, and it helps ionic solids dissolve in water.

Step 1: (Evaluation of Statement A)

(Statement A claims that water is a strong acid and therefore is good at dissolving ionic solids. This statement is not entirely correct. While water can act as both an acid and a base, it is considered a weak acid or base and does not play the primary role in dissolving ionic compounds.)

Step 2: (Evaluation of Statement B)

(Statement B claims that water is good at solvating ions because the hydrogen and oxygen atoms in water molecules bear partial charges. This statement is correct. Water is a polar molecule, meaning it has a partial positive charge on hydrogen atoms and a partial negative charge on the oxygen atom. These partial charges allow water molecules to surround and stabilize dissolved ions, forming hydration shells around them. This process is known as solvation, and it helps ionic solids dissolve in water.)

Step 3: (Evaluation of Statement C)

(Statement C claims that the hydrogen and oxygen bonds of water are easily broken by ionic solids. This statement is not entirely accurate. When ionic compounds dissolve in water, the water molecules do not break their own internal hydrogen and oxygen bonds. Instead, they use their partial positive and negative charges to stabilize the separate ions, allowing the ionic lattice to dissolve.)

Step 4: (Conclusion)

(Based on the analysis of the three statements, option B is the most correct statement about the process of many ionic solids dissolving in water as strong electrolytes. Water's ability to solvate ions is due to the partial charges on hydrogen and oxygen atoms in water molecules, not because it is a strong acid or because its internal bonds are easily broken by ionic compounds.)

Key Concepts

Strong Electrolytes

When we talk about strong electrolytes, we refer to substances that completely dissociate into ions when dissolved in water. This means all the molecules of the ionic compound separate into their respective positive and negative ions.

Because of this complete dissociation, solutions containing strong electrolytes conduct electricity very well. Examples of strong electrolytes include common salts like sodium chloride (NaCl), potassium bromide (KBr), and strong acids like hydrochloric acid (HCl). These substances are vital in various applications, from biological processes in the human body to chemical manufacturing in industries.

Strong electrolytes are against weak electrolytes, which only partially dissociate in solution, leading to poorer electrical conductivity. Understanding the nature of an electrolyte is crucial in predicting how it behaves in a solution. This knowledge helps in fields such as chemistry, medicine, and environmental science.

Polar Molecules

Polar molecules are molecules that have a net dipole moment due to the presence of polar bonds. These polar bonds result from differences in electronegativity between the atoms involved. In polar molecules, one end becomes slightly negatively charged, while the other takes on a positive charge.

Water is a classic example of a polar molecule. It has a bent shape with oxygen at the center and hydrogen atoms on either side. Oxygen is more electronegative than hydrogen, leading to a partial negative charge on the oxygen atom and a partial positive charge on the hydrogen atoms. This polarity is why water is so effective in dissolving many substances.

When polar molecules interact with ionic compounds, they help stabilize ions in the solution by aligning their charges with those of the ions. This interaction is crucial in processes such as solvation, where the polar nature of water molecules plays a key role in dissolving ionic solids.

Solvation Process

The solvation process is a fundamental concept in chemistry that describes how solvent molecules, like water, surround and interact with solute particles. This process is essential for dissolving substances and is driven by the polarity of the solvent molecules.

In the solvation process, water molecules use their partial charges to attract and stabilize ions from the dissociating ionic solid. This attraction forms a 'hydration shell' around each ion. For example, in the dissolution of salt (NaCl), water molecules surround the sodium ions (\[\text{Na}^+\]) and chloride ions (\[\text{Cl}^-\]), stabilizing them in solution.

This stabilization lowers the energy of the system, making dissolution favorable. The solvation process is crucial not only for simple ionic compounds but also in more complex biological and chemical systems. It explains how substances like sugar can dissolve in water and how reactions occur in aqueous solutions.

Understanding the solvation process helps in grasping how solutions form and why certain substances are soluble in particular solvents, providing critical insights for fields ranging from pharmacology to environmental science.