Backnotes

Experimental Techniques

Measuring Mass

  • Balance, Spring Balance, Beam Balance

Measuring Temperature

  • Thermometer

Measuring Time

  • Stopwatch, Clock, Timer

Measuring Volume of Liquids

  • Burette; Good for variable Volumes. 0cm to 50cm
  • Pipette; Good for accuracy. 10cm or 20cm
  • Measuring Cylinder; Good for quick and not accurate. 25cm to 250cm

Measuring Volume of Gases

  • Attach a gas syringe to the end of the apparatus

Paper Chromatography

  • GIVES; Separated substances (different solubilities)
  • FROM; Substances in a Solvent
    • Eg; Different Colour ink
  • A pencil line is drawn on chromatography paper and spots of the sample are placed on it.
  • The paper is  then lowered into the solvent container, making sure that the pencil line sits above the level of the solvent so the samples don’t wash away.
  • The solvent travels up the paper by capillary action, taking some substances with it.
  • Different substances have different solubilities so they will travel at different rates causing the substances to spread apart. Substances with higher solubility will travel further than the others
  • This will show the different components of one sample.
    • Pure substances will show one spot
    • Impure will show more than one
    • If two substances are the same they will produce identical chromatograms

Rf Value

  • It is a value used by chemist to identify components of mixtures
  • It is always the same for a particular substance. Therefore the Rf value of an unknown substance can be compared with one known substance under the same conditions and be identified.
  • Retention Factor= Distance moved by sample/Distance moved by solvent

Locating Agents

  • Some chromatograms will show invisible substances.
  • To solve this, after the chromatogram has been done, the paper is treated with a Locating Agent that will make the sample visible to the naked eye

Purity and its Importance

  • Pure substances have a specific and sharp melting and boiling points
  • Mixtures have a range of melting and boiling points as they consist of different substances that melt and boil at different temperatures
    • Purity is important in food and drugs

Separating Immiscible Liquids

  • Fill a separating funnel with the two liquids (make sure there is a stopcock on the bottom). Then carefully open the stopcock and pour out the less dense substance. Close the stopcock when it is all out

Filtration Method

  • GIVES; Undissolved Solid
  • FROM; Mixture of the solid + liquids/solution
    • Eg; Sand from sand and water
  • Filter paper is placed in a filter funnel above a beaker.
  • Mixture of insoluble solid and liquids is poured in the filter.
  • Filter paper will only allow the liquid to pass as the ‘filtrate’
  • Solid particle will remain on the filter paper as the ‘residue’

Crystallisation Method

  • GIVES; Solid
  • FROM; Solution of dissolved solid and liquid
    • Ex; Salt from Salt and water
  • Solution is heated allowing the solvent to evaporate leaving a saturated solution behind
  • (Test for saturation by dipping a clean dry glass rod into the solution. If crystals form on the glass rod, it is saturated)
  • Allow the saturated solution to cool down. As solubility decreases solid crystals will start to form
  • Collect crystals by filtration, wash them with distilled water to remove impurities and dry them.

Simple Distillation Method

  • GIVES; Liquid
  • FROM; Solution of liquid with dissolved solid
  • OR; Pure liquid from a mixture of liquids
    • Eg; Water from salt water
  • A closed beaker is connected to a condenser, which ends over a beaker.
  • The solution is poured into the closed beaker and heated to the boiling point of the liquid.
  • The liquid will evaporate and enter the condenser, where it will cool down and turn back into a liquid, falling into the beaker.
  • After all the liquid is evaporated, only the solid solute will be left behind

Fractional Distillation Method

  • GIVES; Separated liquids/gases (different Boiling Points)
  • FROM; Liquids that are miscible (mixture)
    • Eg; Ethanol and Water from a mixture of ethanol and water
  • A beaker is connected to a fractionating column which is connected to a condenser which ends in a beaker.
  • The solution is poured into the beaker and heated to the temperature of the substance with the lowest boiling point
  • This substance will rise and evaporate first entering the condenser and turning into a liquid which is collected in the beaker.
  • When all the substance is evaporated and collected, only the other component(s) will be left behind.
    • FRACTIONATING COLUMN;
    • Example; Water (100C) and Ethanol (78C)
    • Because they have close boiling points, also some water will evaporate at 78C. This unwanted water vapour condenses on the glass beads in the column making them hot. When these beads reach 78C, ethanol will no longer condense on them, only the water vapour will. This way, the ethanol reaches the condenser, while the water vapour goes back into the beaker.