Properties of Water- The Universal Solvent: Videos & Practice Problems

Water is known as the universal solvent due to its ability to dissolve various solutes, such as salts and biological molecules. Solvents, like water, are present in larger amounts and facilitate the dissolution of solutes, which are typically found in smaller quantities. Solutions can be classified as homogeneous, where components are evenly distributed, or heterogeneous, where they are not. Additionally, substances are categorized as hydrophilic, which dissolve easily in water, or hydrophobic, which do not mix well with water, impacting biological interactions and processes.

Properties of Water- The Universal Solvent

Water is often referred to as the universal solvent due to its remarkable ability to dissolve a wide variety of substances, which is essential for many biological processes. In this context, it is important to understand the distinction between a solvent and a solute. The solvent is the substance that performs the dissolving, typically present in larger quantities, while the solute is the substance that is dissolved, usually found in smaller amounts.

For example, when table salt (sodium chloride, NaCl) is added to water, the water acts as the solvent, and the salt is the solute. Sodium chloride consists of sodium cations (Na⁺) and chloride anions (Cl^-) that are held together by ionic bonds. However, when salt is introduced to water, these ionic bonds are disrupted. The water molecules surround the sodium and chloride ions, preventing them from recombining into solid salt. This interaction illustrates how water molecules form a hydration shell around the dissolved ions, facilitating the dissolution process.

The resulting mixture of solute and solvent is known as a solution. Specifically, when water is the solvent, the solution is termed an aqueous solution. The term "aqueous" derives from the Latin word for water, highlighting the role of water in these solutions. Understanding these concepts is crucial as they lay the foundation for exploring how water interacts with various biological molecules, including proteins, nucleic acids, and carbohydrates, in subsequent lessons.

A solution in which water is the solvent is called a(n) _______________ solution.

• A. Polar.
• B. Aqueous.
• C. Hydrophobic.
• D. Complete.

Answer: (B)

The substance in a mixture that is dissolved is called the:

• A. Solution.
• B. Solvent.
• C. Solute.
• D. Aqueous solution.

Answer: (C)

What is the charge of the solute molecule in the image below based on the polarity of water?

• A. Positively charged.
• B. Negatively charged.
• C. Uncharged.
• D. Non-polar and hydrophobic.

Answer: (B)

Homogenous vs. Heterogenous Solutions

Understanding the distinction between homogeneous and heterogeneous solutions is fundamental in chemistry. Homogeneous solutions are characterized by a uniform composition, meaning that the components are evenly distributed throughout the mixture. The prefix "homo" signifies "the same," indicating that every part of the solution is identical in composition. For example, when two solutes, such as blue and red particles, are mixed thoroughly in a beaker, they create a homogeneous solution where the colors are uniformly blended.

In contrast, heterogeneous solutions exhibit an uneven distribution of components, where different parts of the mixture can be easily distinguished. The prefix "hetero" means "different," highlighting the lack of uniformity. In a heterogeneous solution, the blue and red solutes may settle in distinct areas of the beaker, with one color concentrated at the top and the other at the bottom, making it clear that the components are not evenly mixed.

Recognizing these differences is crucial for various applications in science and industry, as the properties and behaviors of homogeneous and heterogeneous solutions can significantly impact chemical reactions and processes. As you continue your studies, practicing the identification of these types of solutions will enhance your understanding of mixtures and their characteristics.

The components of a heterogenous solution are ________________ distributed throughout.

• A. Equally.
• B. Unequally.
• C. Uniformly.

Answer: (B)

Hydrophilic vs. Hydrophobic

Understanding the distinction between hydrophilic and hydrophobic substances is essential in the study of chemistry and biology. Water, known as the universal solvent, can dissolve many substances, but it is selective in what it can dissolve. Hydrophilic substances, which means "water-loving," easily dissolve in water due to their affinity for it. The term hydrophilic derives from the Greek words where "hydro" means water and "philic" means loving. Typically, polar and charged substances, such as salts and ions, fall into this category. For instance, when sodium chloride (NaCl) is added to water, the sodium ions (Na⁺) and chloride ions (Cl^-) interact favorably with water molecules, leading to dissolution.

In contrast, hydrophobic substances, meaning "water-fearing," do not dissolve in water. These substances are generally non-polar molecules, which do not interact well with water. Common examples include fats, oils, and waxes. When vegetable oil is mixed with water, it does not blend; instead, it separates, demonstrating its hydrophobic nature. This separation occurs because the non-polar oil molecules do not form favorable interactions with the polar water molecules.

In summary, the key difference lies in the molecular structure and polarity of the substances: hydrophilic substances are typically polar or charged and readily dissolve in water, while hydrophobic substances are non-polar and resist mixing with water. This fundamental concept is crucial for understanding various biological processes and the behavior of different substances in aqueous environments.

Hydrophobic molecules:

• A. Are polar covalent molecules.
• B. Easily dissolve in water.
• C. Are nonpolar water 'fearing' molecules.
• D. Are nonpolar water 'loving' molecules.

Answer: (C)

Here’s what students ask on this topic:

Why is water considered the universal solvent?

Water is considered the universal solvent because it can dissolve a wide variety of substances. This ability is due to its polar nature, where the oxygen atom has a partial negative charge, and the hydrogen atoms have partial positive charges. This polarity allows water molecules to surround and interact with various solutes, such as salts and biological molecules, effectively breaking their bonds and dissolving them. This property is crucial for many biological processes, as it enables the transport and reaction of different molecules within living organisms.

What is the difference between a solvent and a solute?

A solvent is a substance that dissolves other substances, known as solutes. In a solution, the solvent is typically present in a larger amount, while the solute is present in a smaller amount. For example, in a saltwater solution, water acts as the solvent, and salt (sodium chloride) is the solute. The solvent facilitates the dissolution process by surrounding the solute particles and breaking their bonds, leading to a homogeneous mixture.

What are homogeneous and heterogeneous solutions?

Homogeneous solutions are mixtures where the solute is evenly distributed throughout the solvent, resulting in a uniform composition. An example is salt dissolved in water. Heterogeneous solutions, on the other hand, have an uneven distribution of solute particles, leading to a non-uniform composition. An example is a mixture of oil and water, where the oil does not dissolve and remains separate from the water.

What is the difference between hydrophilic and hydrophobic substances?

Hydrophilic substances are water-loving and dissolve easily in water due to their polar nature or charge. Examples include salts and ions. Hydrophobic substances are water-fearing and do not dissolve well in water because they are non-polar. Examples include fats, oils, and waxes. This distinction is important in biological systems, as it affects how molecules interact and function within aqueous environments.

How does water dissolve ionic compounds like sodium chloride?

Water dissolves ionic compounds like sodium chloride (NaCl) by surrounding the individual ions with water molecules. The partial negative charge of the oxygen atom in water attracts the positively charged sodium ions (Na⁺), while the partial positive charge of the hydrogen atoms attracts the negatively charged chloride ions (Cl⁻). This interaction disrupts the ionic bonds in NaCl, leading to the formation of a solution where the ions are evenly distributed and surrounded by water molecules, known as a hydration shell.