Separation techniques Flashcards
Which substances can be sublimed
CO2, Iodine, NH4Cl and naphthalene
Why is crystallisation preferred over evaporation to dryness
It will not thermally decompose substances and no impurities will remain
Criteria for crystallisation to occur
Solubility must change significantly
Which substance can only be separated using evaporation to dryness?
Sodium Chloride
Difference between simple and fractional distillation
Simple distillation: Separate a liquid from a solution(Large difference in boiling point)
Fractional distillation: Separate 2 or more miscible liquids (Small difference in boiling points, <25
Purpose of chromatography
Identify small amounts of substances and locate and separate colourless compunds using locating agent
Factors affecting chromatography
Solubility of solutes in the same solvent , selective adsorption of the solutes by the paper and temperature
Examples of locating agent
Iodine,ninhydrin
How to identify using chromatography?
Identify through comparing with the Rf values of known substances
How to check the number of substances?
Count the dots
What happens if compunds have similar Rf values
Use a new solvent with a different temperature and conduct two-dimensional paper chromatography
Why the bulb of thermometer for fractional distillation must be placed at the entrance of the condenser?
To ensure it is only measuring the temperature of vapours that is distilling and nothing else
Why should water enter through the bottom of the condenser
Ensure condenser is always completetly filled for effective cooling
Purpose of fractionating column
It allows vaporisation and condensation to occur , the glass beads provide a large surfact area for condensation to occur easily
What is the advantage of two-way paper chromatography
Two-way paper chromatography can separate substances with very similar Rf values. Substances may have similar Rf values in one solvent but different Rf values in another solvent
