Chemical analysis Flashcards
What is a pure substance?
chemistry definition
a single element or compound not mixed with any other substances
Describe melting and boiling points of pure substances
- melt and boil at specific temperatures
- solidify and condense at these temperatures
What is the definition of pure substance, in everyday language?
a pure substance can mean a substance that has had nothing added to it, so it is unadulterated and in its natural state
What is an impure substance?
Describe melting and boiling points
mixtures
they do not melt and boul at one temperature - they change state over a range of temperatures
they lower the melting point, increase the melting range of your substances,
increase boiling point, boils at a range of temperatures
What is a formulation?
a mixture that has been designed as a useful product
Most are complex mixtures in which each chemical has a particular purpose.
How are formulations made?
Formulations are made by mixing the components in carefully measured quantities to ensure that the product has the required properties.
What do formulations include? (7)
fuels, cleaning agents, paints, medicines, alloys, fertilisers and foods.
What is chromatography used for?
used to separate mixtures and can give information to help identify substances.
What does separation in chromatography depend on?
the distribution of substances between the mobile and stationary phrase
What is the mobile phase?
the solvent (often water)
molecules can move
What is the stationary phase?
the absorbent paper
does not move
What happens during chromatography in terms of phases?
the substances in the sample constantly move between the mobile and stationary phases = an equilibrium is formed between the two phases
What does the distance up the chromatography paper depend on?
the attraction for the paper and for the solvent
The chemicals that spend more time in the mobile phase than the stationary phase…..
will move further through the stationary phrase
What type of molecules spend more time in the mobile phase?
- molecules with a higher solubility in the solvent and is less attracted to the paper
What does the amount of time the molecules spend in each phase depend on?
- how soluble they are
- how attracted they are to the paper
What is the equation for the Rf value?
distance moved by substance/ distance moved by solvent
What are the properties and test for hydrogen?
- colourless, combines violently with oxygen when ignited
The test for hydrogen uses a burning splint held at the open end of a test tube of the gas. Hydrogen burns rapidly with a pop sound.
What are the properties and test for oxygen?
- colourless, helps fuels burn more readily than in ai
The test for oxygen uses a glowing splint inserted into a test tube of the gas. The splint relights in oxygen
What are the properties and test for Co2?
- colourless
- The test for carbon dioxide uses an aqueous solution of calcium hydroxide (lime water). When carbon dioxide is shaken with bubbled through limewater the limewater turns milky (cloudy).
- connect test tube with a test tube of limewater
What is the test for Chlorine?
The test for chlorine uses litmus paper. When damp litmus paper is put into chlorine gas the litmus paper is bleached and turns white.
What are the different ways you can identify metal ions (cations)
- flame tests
- sodium hydroxide solution
What are the colours produced in a flame test for :
- lithium
- sodium
- potassium
- calcium
- copper
- lithium compounds result in a crimson flame
- sodium compounds result in a yellow flame
- potassium compounds result in a lilac flame
- calcium compounds result in an orange-red flame
- copper compounds result in a green flame.
Name the colour of precipitate produced for each of these metals when they are added to sodium hydroxide solution:
- aluminium
- calcium
- magnesium
- copper (III)
- iron (II)
- iron (III)
Solutions of aluminium, calcium and magnesium ions form white precipitates
only the aluminium hydroxide precipitate dissolves in excess sodium hydroxide solution
Copper(II) forms a blue precipitate,
iron(II) a green precipitate
iron(III) a brown precipitate.
How to test for carbonates?
Carbonates react with dilute acids to form carbon dioxide gas ( +salt and water)
Carbon dioxide can be identified with limewater.
What are carbonates and its properties?
carbonates are substances that contains CO3 (2-) ions
most are insoluble
sodium carbonate and potassium carbonate are soluble and dissolvable in water to form solutions that contain carbonate ions
How to test for Halides?
Halide ions in solution produce precipitates with silver nitrate solution in the presence of dilute nitric acid.
Add a couple of drops of dilute nitric acid, followed by a couple of drops of silver nitrate solution to your unknown solution
What colour precipitate do silver chloride, silver bromide and silver iodide form?
Silver chloride is white,
silver bromide is cream
silver iodide is yellow.
How do you test for sulfates
Sulfate ions in solution produce a white precipitate with barium chloride solution in the presence of dilute hydrochloric acid.
use a pipette to add a couple of drops of dilute hydrochloric acid followed by a couple of drops of barium chloride solution to a test tube containing an unknown solution
What are the advantages of instrumental methods compared with chemical tests
accurate, rapid and sensitive
can be used on small samples
What is flame emission spectroscopy?
How does it work?
Flame emission spectroscopy is an example of an instrumental method used to analyse metal ions in solutions.
The sample is put into a flame and the light given out is passed through a spectroscope.
During flame spectroscopy as the ions heat up, their electrons become excited. When the electrons drop back to their original energy levels, they transfer energy as light
What can flame emisson spectroscopy be used to analyse?
- identify the metal ions in the solution
- measure their concentrations.
