Elements, compounds and mixtures

• An element is a molecule with only one type of atom
• A compound is a molecule with two or more different elements chemically bonded
• A mixture is a substance with two or more different elements or compounds, not chemically joined
• A pure substance has a fixed melting and boiling point but a mixture can have melting points and boiling points on a range due to the different substances in it
• A chromatogram provides information on the contents of a mixture
• Simple Distillation separates two liquids with different boiling points. Heat the solution/mixture with a Bunsen burner and funnel it through a condenser. Collect the liquid with the lower boiling point in a beaker at the end
• Fractional distillation is the process of separating crude oil into groups of hydrocarbons called fractions. put heated crude oil into a fractionating column and heat to 350 degrees at the bottom. The crude oil will evaporate until it reaches a temperature lower than its boiling point, where it will condense and come out of the column
• Filtration separates insoluble solids from soluble liquids. Performed by running the solution through filter paper in a funnel into a beaker
• Crystallisation is a method to separate a soluble solid and a solute through evaporation of the solvent. Put the solution in an evaporating dish and heat with a Bunsen until the solvent has been evaporated
• Chromatography is Used to separate mixtures of soluble substances in a solution. Pin chromatography paper into a beaker with solvent up to a base line drawn in pencil, with samples along it. As the solvent runs up the paper, the inks that are soluble in the solvent will travel up the paper
• Rf values are calculated by dividing the distance travelled by the distance of the solvent both measured from the base line
• How far from the bottom of the paper is the baseline drawn?

  1 cm
• Why should pencil be used instead of ink for the baseline in chromatography?

  Pencil will not dissolve in the solvent
• What happens if ink is used instead of pencil?

  It might dissolve and interfere with results
• Where should the paper be suspended during chromatography?

  In a beaker with solvent
• How should the paper be positioned in relation to the solvent?

  The baseline should be above the solvent level
• Why is it important for the baseline to be above the solvent?

  To prevent dyes from dissolving into the solvent
• What is the purpose of saturating the atmosphere with solvent?

  To prevent solvent evaporation from the paper
• What is drawn on the paper after the solvent has traveled near the top?

  A pencil line to show the solvent front
• What is the term for the line that shows how far the solvent has traveled?

  Solvent front
• What should be done after the chromatogram is removed from the solvent?

  Leave it to dry
• What happens to the solvent after the chromatogram is left to dry?

  All the solvent evaporates
• What are common solvents used in chromatography?

  Water or ethanol
• How does the choice of solvent depend on the dyes?

  It depends on the solubility of the dyes