Question

What properties of water make it useful as a solvent? What types of compound can it (i) dissolve, and (ii) hydrolyse?

Short answer

Water dissolves polar and ionic compounds and can hydrolyze polymers like proteins and carbohydrates.

Step-by-step solution

Understanding Water's Solvent Abilities

Water is a polar molecule, meaning it has a partial positive charge on one end (hydrogen atoms) and a partial negative charge on the other end (oxygen atom). This polarity allows water to interact with and dissolve other polar molecules and ionic compounds.

Identifying Compounds Water Can Dissolve

Because of its polarity, water can effectively dissolve polar substances, such as salts (e.g., sodium chloride) and other polar molecules, like sugars and alcohols. Water's ability to dissolve these substances is primarily due to the formation of hydrogen bonds or ionic interactions that compete with the associations within the solid crystal or molecule.

Understanding Hydrolysis Ability

Water can hydrolyze certain types of compounds. Hydrolysis is a chemical reaction that involves breaking bonds using water. This process is common in breaking down polymers like proteins, carbohydrates, and nucleic acids into their monomers.

Identifying Compounds Subject to Hydrolysis

Compounds that can be hydrolyzed by water typically contain bonds that are susceptible to nucleophilic attack and are often esters, amides, and glycosidic bonds. For instance, peptide bonds in proteins and ester bonds in lipids can be broken down through hydrolysis, often aided by enzymes or acidic/alkaline conditions.

Key concepts

Polar Molecules

At the heart of water's powerful solvent abilities is its nature as a polar molecule. Polarity refers to the presence of distinct and opposing charges on different parts of a molecule. Water has a partial positive charge on its hydrogen atoms and a partial negative charge on its oxygen atom.
This happens because oxygen is more electronegative than hydrogen, pulling the shared electrons closer to itself and creating a dipole moment.
This unique charge distribution allows water to dissolve many substances.

• Polarity helps water interact with other charged or polar molecules, making it effective in dissolving substances like salts, sugars, and acids.
• This interaction often involves the alignment of oppositely charged regions of the molecules, leading to dissolution.

Thus, water excels as a solvent for various polar compounds due to its polar nature.

Hydrogen Bonds

The magic behind water's amazing solvent capacity also lies in hydrogen bonds. These bonds form when the positive region of one molecule interacts with the negative region of another. In water, hydrogen bonds arise from its polar nature.
They occur between the hydrogen atom of one water molecule and the oxygen atom of another.

• Hydrogen bonds are relatively strong for intermolecular forces, which gives water its ability to dissolve both polar and some non-polar substances.
• When water dissolves a substance, it forms a "hydration shell" around ions and polar molecules, effectively separating and surrounding them.

This property allows compounds like salts and organic molecules such as alcohols and sugars to be solubilized in water, greatly enhancing its role as the "universal solvent."

Hydrolysis

Hydrolysis is an essential property of water that involves breaking chemical bonds with the addition of water. This process is critical in many biological and chemical reactions, breaking down complex molecules into simpler components.

• During hydrolysis, water molecules split and attach to bonds, often breaking them.
• This process is crucial in digestion, where polymers like carbohydrates and proteins are decomposed into monomers like glucose and amino acids.

Various bonds are susceptible to hydrolysis, such as ester and amide bonds. For instance, in biology, this reaction is pivotal in DNA and protein synthesis and breakdown.

In essence, hydrolysis showcases water's unique ability to participate in chemical reactions, aiding both in the decomposition of large molecules and in sustaining life processes.