The Solvent: Often, water acts as a universal solvent. Its polar nature (having a slight positive and negative end) allows it to surround and dissolve many ionic and polar covalent compounds. Sodium chloride (table salt) is a classic example. When you dissolve salt in water, the water molecules separate the sodium and chlorine ions, allowing them to move freely in the solution.
The Reactant: However, water can also be a reactant itself, participating directly in a chemical reaction. This happens when the chemical it encounters is highly reactive towards water. Here are some types of reactions:
Metals with water: Highly reactive metals like sodium or potassium react vigorously with water. They displace hydrogen from water, forming metal hydroxides and liberating hydrogen gas. This can be a violent reaction, sometimes with flames.
Acid-Base Reactions: Water plays a central role in these reactions. Acids are defined as substances that donate protons (H+) in water, while bases accept protons. The reaction between hydrochloric acid (HCl) and sodium hydroxide (NaOH) in water is a classic example.
Hydrolysis Reactions: Certain compounds react with water, breaking down into new products. For example, esters can undergo hydrolysis to form an alcohol and a carboxylic acid.
Not all reactions involve change: Sometimes, water simply interacts with a substance without any chemical change. For instance, sugar dissolves in water, but the sugar molecules remain intact.
Here are some additional points to consider:
The reactivity of a substance with water can vary greatly. For instance, some metals like iron rust slowly in moist air, while others like lithium react violently.
It's important to handle water-reactive chemicals with caution as some reactions can be hazardous.