Flashcards in C15: Analysis Deck (40):
What three ions form a white precipitate when reacted with sodium hydroxide solution?
What substance that forms a white precipitate dissolves in excess sodium hydroxide solution?
How can you distinguish between the white precipitate formed by Ca2+ and Mg2+?
What three ions form a coloured precipitate when reacted with sodium hydroxide?
Light green -> brown
Light green -> brown
Test for carbonates
Add dilute acid, if it fizzes and produces CO2 it is a Carbonate.
Test for halides (Bromine, Chlorine, Iodine)
1. Add dilute nitric acid.
2. Add silver nitrate. If a precipitate forms it is a halide.
ALWAYS ADD THE ACID FIRST.
Test for Sulfates
1. Add hydrochloric acid (do this first to remove carbonate ions that would otherwise form a precipitate).
2. Add barium chloride solution.
If a white precipitate forms it is a sulfate. the precipitate formed is Barium Sulfate.
4 techniques for separating mixtures
When is filtration used?
Used to separate substances that are insoluble in a particular solvent from those that are soluble.
> 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.
> 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.
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
> 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.
> 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.
A machine that can be used to analyse small amounts of a substance to identify it and find its relative molecular mass.