Chemical Analysis

• Chemical analysis

  Also known as analytical chemistry, it is about the instruments and methods used to separate, identify and quantify different substances
• Examples of chemical analysis techniques

  1. Paper chromatography for separating different pigments

  2. Filtration and crystallization to isolate solids from liquids

  3. Distillation to separate out different liquids
• Pure substance

  Contains only one type of compound or element, not mixed with anything else
• Examples of pure substances

  • Pure water
  • Pure sodium chloride
• Impure substance

  Mixture of two or more compounds or elements
• Example of impure substance

  • Salt water
• Pure substances

  Melt and boil at specific temperatures
• Impure substances

  Melt and boil over a range of temperatures
• Impurities in a sample

  Lower the melting point but increase the boiling point
• Formulations

  Mixtures that have been prepared using a specific formula to contain precise amounts of different components for a specific function
• The different components in a formulation contribute different properties
• Paper chromatography

  1. Take a piece of filter paper

  2. Draw a line near the bottom (baseline)

  3. Add sample (ink)

  4. Find a beaker and fill with shallow solvent (water or ethanol)

  5. Place filter paper in solvent (but don't submerge baseline and sample)

  6. Wait for solvent to seep up paper
• Chromatogram

  Pattern of spots left on paper after chromatography
• Mobile phase

  Substance (liquid or gas) that the molecules can move in
• Stationary phase

  Substance or material (solid or thick liquid) that the molecules can't move in
• Chemicals spend more time in mobile phase

  They move faster up the paper
• Chemicals spend more time in stationary phase

  They move slower up the paper
• RF value

  Ratio of distance travelled by substance to distance travelled by solvent
• A pure substance with only one chemical won't separate out, just gets a single spot
• Changing mobile or stationary phase changes the RF value for the same substance
• Test for chlorine

  1. Get a test tube of sample gas

  2. Take a piece of blue litmus paper and dampen it

  3. Put the damp blue litmus paper into the test tube

  4. If chlorine is present, the paper will turn from blue to white
• The paper might briefly turn red before turning white, as the chlorine dissolves in the water on the damp paper and forms hydrochloric acid, which is acidic and turns the blue litmus paper red
• Chlorine is poisonous, so you'd want to wear a mask or do the experiment in a fume cupboard
• Test for oxygen

  1. Get a glowing splint (without a flame but still glowing red)

  2. Place the splint into the tube of sample gas

  3. If the gas is oxygen, the glowing splint will relight
• Test for hydrogen

  1. Get a test tube of hydrogen gas

  2. Get a burning splint

  3. Move the test tube and splint close together

  4. You'll hear a squeaky pop as the hydrogen burns with the oxygen in the air to form water
• Test for carbon dioxide

  1. Get a sample of the gas

  2. Get an aqueous solution of calcium hydroxide (lime water)

  3. Bubble the gas sample through the lime water

  4. If the gas is carbon dioxide, the solution will go cloudy as the CO2 and calcium hydroxide react to form calcium carbonate (a solid)
• The cloudiness is due to the solid calcium carbonate particles
• Tests for gases

  • Chlorine
  • Oxygen
  • Hydrogen
  • Carbon dioxide