Topic 10: Qualative Analysis And Nano Particles
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How do you carry out a flame test?
1) light a Bunsen burner and open the air hole to give a hot blue flame. 2) pick a small amount of the substance using a wire loop. 3) hold the sample in the edge of the flame and observe the flame colour.
Why must the wire loop be placed in hydrochloric acid and what is it made of?
It must be cleaned in hydrochloric acid before testing each substance. It is made of platinum so is inert. It also gives no colour to the flame.
Why might nichrome be used instead platinum in the wire loop when flame testing?
It is much cheaper but produces a faint orange flame.
What do flame tests test for?
Cations produces different flame test colours. Flame tests with work with solid samples and with solutions but flame colours from solids are easier to see.
What flame colour does lithium produce?
Red
What flame colour does sodium produce?
Yellow
What flame colour does potassium produce?
Liliac
What flame colour does calcium produce?
Orange-red
What flame colour does copper produce?
Blue-green
Machines can also be used instead of flame tests to analyse substances. Using scientific instruments may improve:
• sensitivity (they can detect much smaller amounts) • accuracy (they give values closer to the true values) • speed.
What is a flame photometer?
Measures the light intensity of the flame colours produced by metal ions. Its data is used to determine the concentration of a metal ion in a dilute solution.
What is calibration curve?
A graph used to determine the concentration of a substance in a sample.
Define the term standard solution:
A solution containing a known concentration of a substance.
How can a metal ion in an unknown solution be identified?
matching its spectrum to that of a known metal ion. (A flame photometer separates out the colours to produce a spectrum of light emitted by each metal ion.
Define the term emission spectra:
A set of wavelengths of light or electromagnetic radiation showing which wavelengths have been given out (emitted) by a substance.
How can water which has been contaminated from waste produced by mines be cleaned?
The polluting metal compounds can be removed by using hydroxide solution. This reacts with the metal ions to produce a precipitate, which settles out and can be removed.
What is a precipitation reaction?
It is a reaction in which an insoluble product is formed from 2 soluble reactants.
How can you test for metal ions?
Sodium hydroxide solution can be used to test for metal ions in a solution. A few drops of hydroxide solution are added to test the solution. Different metal ions produce different coloured hydroxide precipitates.
What precipitate does iron (ll) produce?
Green
What precipitate does iron (lll) produce?
Brown
What precipitate does copper produce?
Blue
What precipitate does calcium produce?
White
What precipitate does aluminium produce?
White
How can you distinguish between aluminium and calcium as they both produce a white precipitate when sodium hydroxide is added to the solution containing those ions?
Aluminium hydroxide disappears to form a colourless solution when excess sodium hydroxide is added to the solution containing aluminium ions. The solution containing calcium ions stays colourless.