Separating Techniques - Topic 1 Flashcards
What is filtration used to separate?
An insoluble solid and a liquid.
Draw a labelled diagram of filtration
What is crystallisation used to separate?
A soluble solid and a solvent (collects solid).
What technique would you use to separate salt from a solution of salt water?
Crystallisation
In crystallisation you heat the solution until it becomes saturated, what does saturated mean?
No more of the solute (the thing that dissolves in the solvent) can dissolve
Once you have formed crystals in crystallisation, to obtain dry crystals you filter them and then place them in what?
A warming or drying oven
Describe the separating technique of crystallisation.
· Heat a solution gently until it becomes a saturated (when no more solute can dissolve) solution.
· Crystals will start to form.
· As the solution cools, the solubility of the solute decreases so more crystals form.
· Filter the crystals. · Dry them in a warming oven.
What is simple distillation used to separate?
It separates a solute from a solution. The solute must have a much lower boiling point than the solvent
Describe simple distillation.
· The solvent boils.
· The vapours pas through a condenser and condense.
· The pure solvent is collected.
What mixtures are separated by fractional distillation?
Two or more liquids that have similar boiling points.
Two or more liquids that have similar boiling points.
Substances with different solubilities e.g. different colours of ink or dye.
What is the mobile phase in chromatography
The solvent (that travels up the paper).
What is the stationary phase in chromatography
The paper
Why should the start line be drawn in pencil?
Because pencil will not dissolve and affect the results
Why should the start line sit above the solvent?
So that the dots of ink or dye do not wash off the paper.
How is the Rf value calculated?
Rf = distance by dye / distance by solvent
What does a high Rf value tell us?
The substance is more soluble and travelled further.
What does a low Rf value tell us?
The substance is less soluble and travelled less distance.
What should the Rf value always be?
A number between 0 - 1
What solvents are used in chromatography?
Water, alcohol, acetone
How can chromatography be used to identify an unknown substance?
Compare with a known substance.
