Separation Techniques Flashcards
Define separation techniques
Separation techniques involve physical methods to separate mixtures into their constituents.
Describe separation of sand from water
Filter the mixture using a filter funnel to obtain sand as residue and water as filtrate
Describe separation of salt from water
Heat the solution in an evaporating dish to evaporate off all the water from the solution to obtain salt.
Describe separation of copper(II) sulfate from water
The solution is heated in evaporating dish to evaporate off most of the water to produce hot saturated solution. Allow the hot saturated solution to cool to form crystals of copper(II) sulfate. Filter the mixture to obtain __ crystals as the residue and dry the crystal between pieces of filter paper
When to use crystallisation over evaporation to dryness
Impurities will remain in the solution and will not crystallise out during crystallisation
Through ETD some solids decompose(thermally unstable)
Solid produced by ETD may not be pure and will be anhydrous
When to use evaporation to dryness over crystallisation
When the solubility of the substance does not change significantly with change in temperature
Why are boiling chips added to mixture in simple distillation
To ensure smooth boiling process
Where should thermometer be positioned in simple distillation and why
Should be positioned with bulb beside the side-arm leading to condenser, ensuring thermometer measures temperature of vapour distilling over to collect boiling point
Why does water enter condenser from bottom and leave from top in simple distillation
To ensure complete condensation of all vapour passing through the condenser
How to collect volatile liquid
Volatile liquid can be kept in liquid state by placing the receiver over ice
Name all magnetic materials
cobalt, Iron, nickel, steel
Name all substances that can sublime
iodine, solid carbon dioxide, naphthalene, ammonium chloride
Define immiscible liquids
Liquids that do not dissolve in each other
Describe using separating funnel
Mixture of immiscible liquids placed in funnel, mixed well and allowed to stand. Liquids form separate layers with less dense liquid being on top of denser one. Stopper removed and tap opened, allow bottom layer to run off and be collected.
Use of fractionating column in fractional distillation
Provides large surface area for condensation of vapours
Why are colourless substances sprayed with locating agent during paper chromatography
To ensure visibility of the substances/compounds
Why should start line be drawn in pencil and not in ink in paper chromatography
Ink may dissolve in the solvent used and thus interfere with the separation of the mixture
Why should start line be above solvent level in paper chromatography
If it is below solvent level, original spot mixture would dissolve in the solvent before it can be separated into its components
Why should original spot mixture be small in paper chromatography
To prevent separated components from ‘overlapping’ onto one another
Why should chromatography paper be sufficiently long in paper chromatography
To ensure complete separation of mixture into components
Why should solvent front reach near the top of chromatography paper in paper chromatography
To ensure complete separation of mixture into components.
Why should a lid cover the container in paper chromatography
To prevent evaporation of the solvent, especially when the solvent is volatile
How to calculate Rf value
Rf value is ratio between distance travelled by substance and distanced travelled by the solvent
What is an advantage of using descending method of chromatography
The solvent flows more quickly as it does not have to move against gravity
If a solid is impure, how is melting point affected
Its melting point is lowered and it melts over a range of temperature
If liquid is impure, how is boiling point affected
Its boiling point is raised and it boils over a range of temperatures
Which common gases are not/very slightly soluble in water
Carbon dioxide, hydrogen, oxygen
How to collect hydrogen(name three)
Displacement of water, downward displacement of air, using graduated gas syringe
Name 3 acidic gases
Carbon dioxide, sulfur dioxide, nitrogen dioxide
Which drying agents are for acidic and neutral gases
Concentrated sulfuric acid and fused calcium chloride
Which drying agents are for alkaline gas
Calcium oxide
Why cant fused calcium chloride be used to dry ammonia
Calcium chloride will react with ammonia
