C12 - Chemical Analysis Flashcards
What is a mixture made up of?
Two or more substances that are not chemically bonded together.
How can mixtures be separated?
By physical separation techniques - there are no chemical bonds between the atoms of the different substances.
What is Filtration?
Involves separating substances that are insoluble in a particular solvent, (e.g sand and water), with a filter funnel and filter paper.
What is Crystallisation?
Involves supplying heat to a solution to obtain a pure, dry sample of a solute (e.g a salt).
You do not need to collect the solvent so it moves into the surroundings.
What is simple distillation?
A method of separation where you need to collect the solvent itself (e.g pure water from salt water), as well as getting the solute.
How does simple distillation work?
1) Solution is heated and boiled to evaporate the solvent.
2) The vapour enters a condenser, a glass tube with 2 inner tubes. The outer tube has water flowing through it that acts as a cooling ‘jacket’ to condense the hot vapour.
3) The hot vapour cools down and is condensed back into a liquid for collection.
What technique is used to separate miscible (mixed) liquids?
Fractional Distillation
What causes the liquids to separate in fractional distillation?
The different boiling points of the liquids in the mixture cause the liquids to separate.
How does fractional distillation work (e.g ethanol and water)?
1) The mixture of ethanol and water is heated.
2) The vapour moves up the fractioning columns through the *glass beads.
3) The fractioning column is hottest at the bottom.
4) The substance with the lower boiling point (ethanol) reaches the top of the column and condenses into a liquid which is collected.
Why are glass beads placed in the fractioning column?
The beads provide a large surface area for hot vapours to cool and condense.
Why is the susbstance with the lowest boiling point collected more easily?
Because it moves higher up the fractioning column (cooler at the top) and reaches the condenser, where it is condensed into a liquid.
E.g Ethanol has a lower BP (78°C) than water (100°C)
What is Paper Chromatography?
A process that separates mixtures of substances dissolved in a solvent as they move up a piece of chromatography paper.
Why do the susbstances separate on the paper?
Because of their different solubilities in the solvent.
The more soluble a susbstance is in a solvent, the further up the paper it goes.
How should you carry out Paper Chromatography?
1) Use a capillary tube to dab a spot of the solution on the line (pencil) near the bottom of a sheet of absorbent chromatography paper.
2) Place the paper standing in the solvent at the bottom of the beaker.
3) Observe what happens.
More soluble = further up the paper.
What are the 2 methods of testing for the positive ions present in unknown compounds - RP7?
- 1) Flame Tests - colour of flame
2) Sodium Hydoxide reaction - colour of the precipitate formed
*Always try Flame Tests first
What are the 3 methods of testing for the negative ions present in unknown compounds - RP7?
1) Carbonates - add dilute acid; if present it fizzes (CO2) - CAWCS
2) Halides - add dilute nitric acid and then silver nitrate solution; if present colour of precipitate indicates what halide it is.
3) Sulfates - add hydrochloric acid, followed by a barium chloride solution; if present should produce a white precipitate of barium sulfate
What are the colours of the flame for Lithium, Sodium, Potassium, Calcium and Copper ions?
Li+ = Crimson Red Na+ = Yellow K+ = Lilac Ca2+ = Orange-Red Cu2+ = Green
What is the colour of the precipitate when you react sodium hydroxide with aluminium, calcium or magnesium?
White
What are the different colours of the precipitate when you react sodium hydroxide with copper (II), iron (II) and iron (III)?
Cu2+ = Blue precipitate Fe2+ = Green precipitate Fe3+ = Brown precipitate
