Chemistry+Lab+Techniques

=Chemistry Lab Techniques=

A series of critical laboratory skills are required in an organic lab setting. Many of these skills may not seem pertinent to a materials scientist. However, the principles exploit fundamentals that have universal application. Some of these principles will be discussed. toc

Principles

 * Boiling point: occurs when the vapor pressure equals the external pressure. It is applied in refluxing.
 * Melting temperature - purification
 * Diffusion - chromatography
 * Polarity - TLC, reflux condensation
 * Solubility - purification, separation
 * Miscibility - purification...
 * Phase transformation - recrystallization
 * pH - titrations, buffers

Filtration
Filtration employs methods to purify a sample for impurities
 * Micro-scale filtration: uses a filter pipette and celite. A bulb can be used to expedite the process.
 * Gravity filtration: uses fluted filter paper and flask.
 * Vacuum filtration: an aspiration process using a side arm flask, trap an either a Buchner or Hirsch funnel

Separation

 * Chromatography
 * Distillation

Distillation
Distillation is a technique used to separate or purify two liquids based on its boiling point.
 * ~ Type ||~ Criteria ||~ Principle ||
 * Simple || * miscible liquids
 * bp < 150°C at 1 atm
 * > bp Δ25°C || Boiled solution evaporates, then condenses through a water cooled condenser. The distillate is collected. ||
 * Fractional || * miscible liquids
 * < bp Δ25°C || A fractional column is used, having increased surface area, to purify distillate as it moves up the column. ||
 * Vacuum || * miscible liquids
 * bp > Δ150°C at 1 atm || At high boiling points, a substance can undergo decomposition. By reducing the pressure with a vacuum, the boiling point is suppressed. ||

Refluxing
Refluxing enables heating of chemicals in a contained environment without evaporation or pressure build up in the container. This is accomplished by boiling the solution and continuously condensing with cooling water. Approximately 80% of all chemistry experiments employ this technique.

Bumping can be observed. This is the bubbling of solution due to superheating which can result in lose of material. Bumping is reduce by using a stir bar or boiling stones. Both add turbulence either mechanically or through small air bubble generation respectively.