verifying components and purity - Unit 4 AOS 2

Question 1

melting point to determine purity

Answer 1

• Melting point determination involves the measurement of the temperature at which a solid compound changes from a solid to a liquid state.
• Pure substances have a sharply defined melting point (within a very small temperature range of 1–2 °C), while impure substances have both a lower and broader melting temperature.
• The melting point of an impure compound is less (termed ‘melting point depression’) than a pure compound due to the impurities disrupting and weakening the overall molecular or lattice structure, meaning less energy is required to overcome the forces of attraction in the solid, thereby causing it to melt.

Question 2

applications of melting points

Answer 2

• thieli tube
• metal block
• electronic device

Question 3

distillation

Answer 3

• Distillation is a process used to separate and verify components of a liquid mixture based on their different boiling points.

Question 4

simple distillation

Answer 4

• Simple distillation uses the apparatus illustrated in to separate one component from a mixture.
• Simple distillation is also commonly used to separate the solute (a solid) from the solvent (a liquid), which is not possible using fractional distillation.
• Simple distillation is most effective at enriching the more volatile compound when the boiling points of the components differ by at least 100 °C
• the more volatile substance will evaprtate and can be codensed back to a liquid and collected, leaving the less volatile subtance

Question 5

fractional distillation

Answer 5

• Fractional distillation is a modified form of simple distillation that effectively allows multiple rounds of
  distillation to occur without having to move the distillate back to the distilling flask. it can sepeartae several compounds with very similar boiling points
• There is also a temperature gradient caused by the ascending vapour, moving from the hotter base to the cooler top of the column. It is these two features of fractionating columns that allow the repeated boil–condense cycles, which have a similar effect to multiple rounds of distillation
• the substance with the lowest boiling point rises to the top