Understanding Mixtures and Solutions: Types and Separation
Mixtures and Solutions
Mixtures are combinations of several pure substances that do not interact chemically. The proportion between the different substances can vary widely, but each retains its composition and properties.
Homogeneous Mixtures
In homogeneous mixtures, the compounds are uniformly disseminated. Any portion of the mixture has the same chemical composition and identical properties. In this case, the mixture is said to have a single phase.
Heterogeneous Mixtures
In heterogeneous mixtures, the different components are not uniformly dispersed. They can be distinguished at first sight or with optical instruments, revealing more than one phase. Each phase of the mixture has a different composition and properties.
Solutions
A solution is a homogeneous mixture of two or more substances. The major component is called the solvent, and the minor component(s) are called the solute(s). Although the solute and solvent can have any physical state, the solution always presents the physical state of the solvent. Based on this state, solutions can be classified as gaseous, liquid, or solid.
Types of Solutions (Solute/Solvent)
- Solid: Alloys, amalgam (Hg in Au), hydrogen in palladium.
- Liquid: Sugar in water, ethanol in water, oxygen in water.
- Gas: Sublimed iodine in air, water vapor in air, air.
Solubility
The solubility of a solute in a solvent is defined as the maximum amount of solute that can dissolve in a given amount of solvent at a certain temperature. Solubility depends on the characteristics of both the solute and solvent, as well as the temperature.
Generally, when dissolving a solid in a liquid, the higher the temperature, the higher the solubility. The representation of the solubility of a substance based on temperature is called the solubility curve. The curve indicates the maximum amount of substance that can be dissolved at each temperature.
When dissolving gases in liquids, solubility depends on the pressure of the gas and the liquid’s temperature. The solubility of a gas in a liquid decreases with increasing temperature.
Types of Solutions Based on Solute Concentration
- Diluted: Contains a low proportion of solute.
- Concentrated: Contains a high proportion of solute.
- Saturated: The solvent cannot dissolve any more solute at a given temperature.
- Unsaturated: Can still dissolve more solute.
- Supersaturated: Contains more solute than it would normally hold at saturation. This state is very unstable.
Separation of Compounds in a Mixture
To study a substance, it needs to be in a pure state. Therefore, separating the components of a mixture is a common task in laboratories and chemical industries. To separate the components, one must consider that each component has certain properties that distinguish it from others. These differences can be used to devise a separation procedure. Depending on the complexity of the mixture, the procedure may consist of several steps.
Separation Techniques
- Heterogeneous Mixtures: Filtration, decantation, sedimentation, centrifugation.
- Homogeneous Mixtures: Evaporation, distillation, liquid-liquid extraction, solid-liquid extraction, crystallization, chromatography.
Exercises
The following examples illustrate how to apply separation techniques:
- Sand + Glass: (No separation method given, needs clarification)
- Glass + Sand + Sugar + Water: Decanting
- Sugar dissolved in water: Evaporation
- Salt + Salt: (Redundant, needs clarification)
- Sulfur + Ethanol: (No separation method given, needs clarification)
- Sand + Iodine in Ethanol: Evaporation
- Iodine + Water + Ethanol + Sand: (No separation method given, needs clarification. Likely a multi-step process)
- Salt + Salt Water: Evaporation
- Iron Filings + Sand: Magnet
- Acetone + Sand: Filtration
- Water + Acetone: Distillation
- Sand + Water: Filtration
- Salt + Sand + Alcohol: Filtration, then distillation of alcohol, then evaporation of water to leave salt.
- Water + Iron + Gasoline: Filtration, then extraction.
- Salt + Water + Gasoline: Extraction, then evaporation of water to leave salt.
- Ash + Water + Potash: Evaporation of water to leave potash and ash.
- Coal + Water: (No separation method given, needs clarification. Likely filtration)