C8

• Chromatography is a general analytical technique used to separate different substances in a mixture to identify them
• Paper chromatography is used to separate different dyes in an ink
• Steps of paper chromatography:

  • Draw a baseline near the bottom of a piece of filter paper
  • Add the ink sample to the pencil line
  • Place the filter paper in a beaker with a shallow amount of solvent like water or ethanol, ensuring the pencil line and ink spot are not submerged
  • Wait for the solvent to seep up the paper, separating the dyes as they dissolve and move up at different rates
• The mobile phase in chromatography is the substance that molecules can move in, usually a liquid or gas, like the solvent used in paper chromatography
• The stationary phase is a substance or material that molecules can't move in, usually a solid or thick liquid, like the paper in paper chromatography
• Chemicals in a sample during chromatography constantly change between the mobile and stationary phases, dissolving in the solvent, moving a bit, and binding to the paper repeatedly
• The time spent in each phase determines how fast chemicals move up the paper, with more soluble chemicals moving faster in the mobile phase and less soluble ones moving slower in the stationary phase
• To compare substances in chromatography, the ratio called the rf value is calculated as the distance traveled by the substance divided by the distance traveled by the solvent
• When doing chromatography with a pure substance, it won't separate out or will show a single spot on the chromatogram with a specific rf value
• If the experiment is repeated with the same substance but different solvent or paper, the chromatogram and rf value may change due to altering the mobile or stationary phase
• Chemical analysis


  Involves instruments and methods used to separate, identify, and quantify different substances
• Examples of chemical analysis methods

  • Paper chromatography for separating different pigments from a mixture
  • Filtration and crystallization to isolate solids from liquids
  • Distillation to separate out different liquids
• Chemical tests


  Used to identify common gases
• Pure substance


  Contains only one type of compound or element and isn't mixed with anything else
• Only pure substances melt and boil at specific temperatures
• Impure substances melt and boil over a range of temperatures depending on the mixture
• Impurities in samples

  Lower the melting point but increase the boiling point
• Formulations


  Mixtures prepared using a specific formula to contain precise amounts of different components for a specific function
• Components in formulations

  Always present in the same proportions and contribute different properties
• Making formulations


  Like following a recipe to create a specific mixture for a particular purpose
• Chromatography


  General analytical technique used to separate different substances in a mixture to identify them
• Types of chromatography

  • Paper chromatography
• Paper chromatography

  1. Draw a baseline near the bottom of filter paper

  2. Add sample of ink to the baseline

  3. Fill a beaker with a shallow amount of solvent

  4. Place filter paper into the solvent without submerging the baseline and ink spot

  5. Wait for solvent to seep up the paper, separating out different dyes

  6. Remove paper when solvent almost reaches the top and leave it to dry
• Chromatogram is the pattern of spots left on the paper after chromatography
• Mobile phase

  Substance (liquid or gas) in which molecules can move, in paper chromatography, it is the solvent used
• Stationary phase


  Substance or material (solid or thick liquid) in which molecules cannot move, in paper chromatography, it is the paper
• Properties of substances determine how fast they move up the paper in chromatography

  More soluble substances move faster (spend more time in mobile phase), less soluble substances move slower (spend more time in stationary phase)
• Rf value is calculated as the distance travelled by the substance divided by the distance travelled by the solvent
• Chromatography with a pure substance results in no separation or a single spot on the chromatogram with a specific rf value
• Changing the solvent or type of paper in chromatography experiment can alter the chromatogram and rf value
• Match the letters A to C on the diagram above with the following descriptions:

  Insoluble parts of the ink: C

  Substance with the a relatively slow rate of travel: B

  Substance with a relatively fast rate of travel: A

  
• What's this

  chromatogram

  
• A substance which is more soluble in the mobile phase will spend more time in the mobile phase. This means it will move faster, and travel a further distance up the paper.
• A substance which is less soluble in the mobile phase will spend more time in the stationary phase, so move slower, and not travel very far up the paper
• rf formula


  Rf​ = distance travelled by the solvent / distance travelled by the substance​
• Test for chlorine


  1. Take a test tube full of the sample gas suspected to contain chlorine

  2. Dampen a piece of blue litmus paper

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

  4. If chlorine is present, the paper will turn from blue to white

  5. Note: the paper may briefly turn red before turning white due to the formation of hydrochloric acid and bleaching by chlorine

  6. Remember that chlorine is poisonous, so precautions like wearing a mask or using a fume cupboard are necessary
• Test for oxygen

  1. Use a glowing splint

  2. Place the glowing splint into the tube with the gas sample

  3. If the gas is oxygen, the splint will relight due to the presence of oxygen supporting combustion
• Test for hydrogen

  1. Use a burning splint

  2. Bring the burning splint close to the test tube containing hydrogen

  3. A squeaky pop sound will be heard as hydrogen burns with oxygen to form water
• Test for carbon dioxide


  1. Have the gas sample in one tube and an aqueous solution of calcium hydroxide (lime water) in another

  2. Bubble the gas sample through the calcium hydroxide

  3. If the gas is carbon dioxide, the solution will go cloudy due to the formation of calcium carbonates and water
• Chlorine turns blue litmus paper white