MYP Integrated Sciences Filtration, Distillation and Chromatography Notes

Filtration, Distillation and Chromatography

Separation techniques are all about taking mixtures apart using differences in physical properties such as particle size, boiling point, solubility and adsorption.

What Physical Properties Does Each Technique Use?

Filtration

1. What it relies on:
   1. Solid particles being larger than the pores in the filter.
   2. Liquid particles being small enough to pass through.
2. How filtration works:
   1. The mixture is poured into filter paper in a funnel.
   2. Liquid passes through and is collected as the filtrate.
   3. Solid particles are trapped on the paper as the residue.

Distillation

1. What it relies on:
   1. One component having a lower boiling point and therefore being more volatile (evaporates first).
   2. The vapour being condensed back to a liquid and collected separately.
2. Simple distillation
   1. Used when the boiling points are far apart (e.g. water and dissolved salt):
      1. Heat the mixture.
      2. The lower-boiling liquid vaporises first.
      3. The vapour passes into a condenser, cools and becomes distillate.
      4. Less volatile components stay behind.
3. Fractional distillation
   1. Used when boiling points are close together (e.g. ethanol and water):
      1. A fractionating column is added.
      2. Vapours repeatedly evaporate and condense along the column.
      3. Components separate into fractions based on their boiling points.

Chromatography

1. Different substances:
   1. That are more soluble in the mobile phase move further.
   2. That stick more strongly to the stationary phase move less.
2. Key physical ideas
   1. Solubility in the solvent.
   2. Affinity/adsorption to the stationary material.
   3. Diffusion and movement of particles.

How Do We Interpret Chromatograms?

A chromatogram is the pattern of separated spots or bands produced after a chromatography run.

Basic features of a chromatogram

1. Base line / origin – where the sample was originally spotted.
2. Solvent front – how far the solvent has travelled.
3. Spots / bands – where each component has moved to.

Using $R_f$ values

1. To make chromatograms comparable, chemists use the retention factor ($R_f$): $$R_f=\frac{\text { distance moved by substance }}{\text { distance moved by solvent front }}$$
2. $R_f$ is always between 0 and 1.
3. A higher $R_f$ means the substance is more soluble in the solvent / less strongly adsorbed to the stationary phase.
4. A lower $R_f$ means the substance is less soluble / more strongly held by the stationary phase.

Comparing Relative Solubilities And Affinities

1. On a chromatogram:
   1. Spots that travel furthest:
      1. Most soluble in the mobile phase
      2. Least strongly adsorbed to the stationary phase
   2. Spots that travel least:
      1. Least soluble
      2. Most strongly adsorbed
2. So just by looking at how far each spot has travelled, we can rank substances by relative solubility and affinity.

Real-Life Uses of These Techniques

Filtration In Real Life

1. Water treatment – removing sand, silt and solid impurities.
2. Air filters – trapping dust and particulates from air.
3. Pharmaceuticals – removing undissolved solids from drug solutions.
4. Everyday – coffee filters, tea strainers, pool filters.

Distillation In Real Life

1. Water purification – making distilled/sterile water.
2. Petroleum industry – fractional distillation of crude oil into petrol, diesel, kerosene, etc.
3. Food & drink – concentrating alcoholic beverages (e.g. spirits).
4. Chemical manufacture – purifying solvents and reagents by boiling point.

Chromatography In Real Life

Chromatography shines in analysis rather than bulk separation.

1. Environmental monitoring
   1. Detecting pesticides in river water
   2. Measuring pollutants like heavy metals or organic toxins
   3. Checking air samples for volatile organic compounds (VOCs)
2. Food testing
   1. Checking for artificial food colourings or banned dyes.
   2. Measuring levels of additives, preservatives or sweeteners.
   3. Ensuring products are free from contaminants such as pesticide residues.
3. Forensic science
   1. Chromatography is widely used to:
      1. Compare ink samples from pens and documents (e.g. in forgery cases).
      2. Analyse drug samples and identify unknown substances.
      3. Examine explosive residues or trace chemicals at crime scenes.