C15: Analysis Flashcards
Lithium (Li+)
Crimson
Sodium (Na+)
Yellow
Potassium (K+)
Lilac
Calcium (Ca2+)
Brick Red
Barium (Ba2+)
Apple Green
What three ions form a white precipitate when reacted with sodium hydroxide solution?
Al3+
Ca2+
Mg2+
What substance that forms a white precipitate dissolves in excess sodium hydroxide solution?
Al3+
How can you distinguish between the white precipitate formed by Ca2+ and Mg2+?
Flame Test
What three ions form a coloured precipitate when reacted with sodium hydroxide?
Cu2+
Fe3+
Fe2+
Fe2+
Light green -> brown
Light green -> brown
Fe2+
Fe3+
Reddish brown
Reddish brown
Fe3+
Cu2+
Light blue
Light blue
Cu2+
Crimson
Lithium (Li+)
Yellow
Sodium (Na+)
Lilac
Potassium (K+)
Brick Red
Calcium (2+)
Apple Green
Barium (2+)
Test for carbonates
Add dilute acid, if it fizzes and produces CO2 it is a Carbonate.
Test for halides (Bromine, Chlorine, Iodine)
- Add dilute nitric acid.
- Add silver nitrate. If a precipitate forms it is a halide.
ALWAYS ADD THE ACID FIRST.
Chloride
White
White
Chlorine
Bromine
Cream
Cream
Bromine
Iodine
Yellow
Yellow
Iodine
Test for Sulfates
- Add hydrochloric acid (do this first to remove carbonate ions that would otherwise form a precipitate).
- Add barium chloride solution.
If a white precipitate forms it is a sulfate. the precipitate formed is Barium Sulfate.
4 techniques for separating mixtures
> Filtration
Crystallisation
Distillation
Chromatography
When is filtration used?
Used to separate substances that are insoluble in a particular solvent from those that are soluble.
Crystallisation
> Water is evaporated through heating in an evaporating dish on a water bath. (gentler form of heating)
When small crystals begin to form, heat is removed and solution is left to evaporate at room temperature. This last step should take place in a flat bottomed or petri dish to increase surface area for evaporation.
Distillation
> Solution is heated until the substance with the lower boiling point evaporates.
Gas gets passed into a condenser and is surrounded with cold water.
A pure, liquid substance will come out.
Chromatography
The process whereby small amounts of dissolved substances are separated by running a solvent along a material such as absorbent paper.
R(f) Retention Factor
Distance a spot has been carried above the baseline/ distance of the solvent front.
Benefits of modern chromatography methods
> Highly accurate and sensitive
Quicker
Enable very small samples to be analysed
Benefits of classic chromatography methods
> Less expensive
Don’t take the special training required by modern techniques.
Results of modern chromatography can often only be interpreted in comparison with data from known substances.
Gas chromatography
> Sample mixture is vaporised.
a ‘carrier gas’ moves the vapour through the coiled column.
Compounds that are more attracted to the material in the column will take longer to come out (have a longer retention time).
Substances can be identified by comparing their retention time to that of known substances.
Mass Spectrometry
A machine that can be used to analyse small amounts of a substance to identify it and find its relative molecular mass.
Where is the molecular ion peak located on a graph?
The last peak on the right as you look at a mass spectrum.
