purity and seperation

Cards (42)

  • a pure substance
     consists of a single element or compound which contains no other substances
    • A mixture consists of two or more elements or compounds that are physically mixed together, they are not chemically combined
  • what is air?
    a mixture
    • Pure substances melt and boil at specific and sharp temperatures e.g. pure water has a boiling point of 100°C and a melting point of 0°C
    • Mixtures have a range of melting and boiling points as they consist of different substance that tend to lower the melting point and broaden the melting point range
  • how can you use melting/boiling points to distinguish pure substances from mixtures?
    if the substance has a range of melting/boiling points = impure
  • does this cooling graph show a pure or impure substance?
    pure because the horizontal part of the graph shows that the compound has a sharp melting point
  • does this cooling graph show a pure or impure substance?
    impure because there is a gradual decrease in temperature due to the range of melting points.
  • percentage range = (final value - original value) / original value x 100
  • symbol for relative atomic mass?
    Ar.
  • what is the relative atomic mass?
    the average mass of the atoms of an element measured relative to the mass of carbon-12
  • what is the relative molecular mass?
    the average mass of the atoms of one molecule or compound measured relative to the mass of one atom of carbon-12
  • symbol for relative formula mass?
    Mr and it refers to the total mass of the molecule
    • Empirical formula is the simplest whole number ratio of atoms of each element in a molecule 
    • The molecular formula tells you the actual number of atoms of each element in a molecule
  • how to find percentage composition?
    % mass of an element = (Ar x no. of atoms of the element) / Mr of the compound x 100
    • An alloy is a mixture of metals
    • Alloys are also an example of a formulation
    • A formulation is a mixture that has been designed as a useful product 
    • Most metals are too soft to use on their own and are mixed with other elements to make them stronger and harder
    • Alloys contain atoms of different sizes, which distorts the regular arrangements of atoms
    • This makes it more difficult for the layers to slide over each other, so they are usually much harder than the pure metal
  • filtration
    • Used to separate an undissolved solid from a mixture of the solid and a liquid / solution ( e.g. sand from a mixture of sand and water)
  • fill in the gaps!
    A) filter funnel
    B) filter paper
    C) liquid only (filtrate)
    D) insoluble solid and liquid
  • Crystallisation
    • Used to separate a dissolved solid from a solution, when the solid is much more soluble in hot solvent than in cold
  • fill in the blanks
    A) crystallised solute
    B) the solute will slowly crystallise
  • Simple Distillation
    • This is used to separate a liquid and soluble solid from a solution (e.g., water from a solution of salt water) or a pure liquid from a mixture of liquids
  • fill in the blanks!
    A) pure water vapour
    B) salty water
    C) pure water
    D) vapur condenses in condenser
    E) 100 degrees
  • Fractional Distillation
    • This is used to separate two or more liquids that are miscible with one another (e.g., ethanol and water from a mixture of the two)
  • chromatography is used to separate substances and provide information to help identify them.
  • the components of chromatography have different what?
    solubilities in a given solvent
  • why is a pencil used in chromatography?
    the ink from a pen would run into the chromatogram along with the sample
  • if a substance has a higher solubility what will it do?
    travel further than others
  • what are the 2 phases in all types of chromatography?
    mobile and stationary
  • what is the mobile phase in paper chromatography?
    the solvent in which the sample molecules move - the liquid
  • what is the stationary phase in paper chromatography?
    chromatography paper
  • what is the stationary phase in thin-layer chromatography?
    a thin layer of an intert substance (like silica) supported on a flat unreactive surface
  • what is the mobile phase in thin layer chromatography?
    the solvent, the liquid
  • how to calculate the retention factor?
    distance moved by compound / distance moved by solvent
  • when is gas chromatography used?
    to seperate a mixture of gases
  • what is the mobile phase in gas chromatography?
    unreactive carrier gas (such as nitrogen)
  • what is the stationary phase in gas chromatography?
    a thin layer of an unreactive liquid e.g. silica
  • what does the number of peaks tell you?
    number of compounds in mixture