When salt is added to water, it forms a solution. The salt particles completely and evenly disperse throughout the water, creating a uniform, homogeneous mixture. The original components remain present, as no new chemical compound is formed.
What is a Mixture?
A mixture involves two or more substances that are combined physically, but they do not chemically bond. Each component within a mixture retains its original chemical identity and properties. These substances can often be separated from each other using physical methods, such as filtration or evaporation. Mixtures can be categorized into two types: heterogeneous and homogeneous. In a heterogeneous mixture, the components are not evenly distributed, and individual parts can often be seen. Examples include sand mixed with water, or a salad with various visible ingredients.
What is a Solution?
A solution is a specific type of homogeneous mixture, characterized by its uniform composition. In a solution, one substance, known as the solute, completely dissolves into another substance, called the solvent. The solute particles become dispersed at a molecular or ionic level, making them invisible to the naked eye.
Solutions can exist in various states, including solids, liquids, and gases. Examples include air (gaseous), brass (solid), and sugar dissolved in water (liquid). The components of a solution cannot be easily separated by simple physical means like filtration, and the dissolved particles do not settle over time.
Why Salt and Water Form a Solution
When table salt (sodium chloride or NaCl) is added to water, it forms a solution because of the unique properties of both substances. Sodium chloride is an ionic compound composed of positively charged sodium ions (Na+) and negatively charged chloride ions (Cl-), held together by ionic bonds. Water is a polar molecule, meaning it has a slightly positive end and a slightly negative end.
This polarity allows water molecules to interact strongly with the charged salt ions. The positive ends of water molecules are attracted to the negative chloride ions, while the negative ends are attracted to the positive sodium ions. These attractions are strong enough to overcome the ionic bonds holding the salt crystal together, pulling individual ions away from the salt crystal lattice.
This process, called hydration, involves water molecules surrounding each separated ion, preventing them from rejoining to form solid salt again. The ions become evenly dispersed throughout the water, creating a uniform mixture where the salt appears to “disappear.” This forms a stable homogeneous solution, with the salt’s ions simply distributed throughout the water.