Separating techniques Flashcards
What separates a LIQUID from a soluble solid in a solution (water from a salt solution)?
Simple distillation
What separates two or more liquids that are miscible (can mix together) with one another (water and ethanol from a mixture of the 2)?
Fractional distillation
What separates an undissolved solid from a mixture of the solid and a liquid (sand from sandy water)?
Filtration
What separates a dissolved SOLID from a solution?
Crystallisation
What is used to separate substances that have different solubilities in a given solvent (different coloured inks mixed to make black ink)?
Chromatography
Describe how to carry out a chromatography to investigate different inks
Draw start line in pencil using a ruler.
Place spots of ink on start line.
Place paper in beaker with start line above solvent.
Remove paper when solvent almost reaches top of paper
Mark solvent front on paper.
Remove paper from beaker and allow to dry
What does it mean if a dye moves the furthest from the start line during a chromatography?
It is the most soluble in solvent.
What role does the condenser play in simple and fractional distillation?
Cools the water vapour so it condenses and can be collected as a liquid.
Why, in chromatography, must the pencil start line sit above the level of the solvent?
So the samples of dye placed along start line don’t wash into the solvent
Why, in chromatography, is a pencil used for the start line?
Ink would run into the chromatogram along with the samples. Pencil isn’t soluble.
What is the difference between crystallisation and simple distillation (in terms of what the products are, what is separated)?
Simple distillation separates the liquid from the solution of soluble solid and liquid.
Crystillasation separates the soluble solid from the solution of soluble solid and liquid
How do you calculate the Rf value of a dye in chromatography?
Divide distance travelled by the particular dye by distance travelled by the solvent, both measured from start line.
Describe fractional distillation (small scale, not crude oil)
The solution is heated to the temperature of the substance with the lowest boiling point
This substance will rise and evaporate first, and vapours will pass through a condenser, where they cool and condense, turning into a liquid that will be collected in a beaker
All of the substance is evaporated and collected, leaving behind the other components(s) of the mixture
Describe simple distillation
The solution is heated, and pure water evaporates producing a vapour which rises.
The vapour passes through the condenser, where it cools and condenses, turning into the pure liquid that is collected in a beaker
After all the water is evaporated from the solution, only the solid solute will be left behind
Describe crystillasation
The solution is heated, allowing the solvent to evaporate, leaving a saturated solution behind
Test if the solution is saturated by dipping a clean, dry, cold glass rod into the solution
If the solution is saturated, crystals will form on the glass rod
The saturated solution is allowed to cool slowly
Crystals begin to grow as solids will come out of solution due to decreasing solubility
The crystals are collected by filtering the solution, they are washed with cold distilled water to remove impurities and are then allowed to dry
