Chemical Analysis Flashcards
describe the test for hydrogen
- Remove the bung from the test tube and insert a burning splint
- If hydrogen is present, the hydrogen gas burns rapidly and will produce a pop sound
describe the test for oxygen
- use glowing splint and place into test tube of “ oxygen “, if oxygen is present the splint relights and bursts into flames
describe the test for carbon dioxide
- limewater used ( limewater is an aqueous solution of calcium hydroxide)
- two test tubes are present ( one w the gas and one w limewater
- draw some of gas into plastic pipette
- Bubble/shake the gas through limewater
- if repeated several times the limewater will turn cloudy( milky)
describe the test for chlorine
- Insert damp litmus paper into the mouth of the test tube
Chlorine bleaches the litmus paper and turns it white
in the flame test what colour does lithium produce
crimson flame
in the flame test what colour does sodium produce
yellow flame
in the flame test what colour does potassium produce
lilac flame
in the flame test what colour does calcium produce
orange-red flame
in the flame test what colour does copper produce
green flame
what solution can be used to identify metal ions
sodium hydroxide solution
what colour is formed when sodium hydroxide solution is added to aluminium, calcium and magnesium
white precipitate
what is an issue of calcium , aluminium and magnesium when sodium hydroxide solution is added to them
they all produce a white precipitate = hard to distinguish
how can we distinguish between aluminium , magnesium and calcium
- if added excess sodium hydroxide is added to aluminium = aluminium precipitate redissolves
Flame test needs to be done to distinguish calcium
what is the balanced equation of adding calcium nitrate with sodium hydroxide
calcium nitrate + sodium hydroxide —> sodium nitrate + calcium hydroxide
what is the balanced equation of adding magnesium nitrate with sodium hydroxide
magnesium nitrate + sodium hydroxide –> sodium nitrate + mangesium hydroxide
what is the balanced equation of adding aluminium nitrate with sodium hydroxide
aluminium nitrate + sodium hydroxide —> sodium nitrate + aluminium hydroxide
what does the reaction of copper 11 ( 2) ions and sodium hydroxide produce
a blue precipitate of copper 11( 2) hydroxide
what does the reaction of iron 11 ( 2) ions and sodium hydroxide produce
green precipitate of iron 11 ( 2) hydroxide
What does the reaction of iron 3 ions and sodium hydroxide produce
brown precipitate of iron (111) hydroxide
what is the balanced symbol equation for the reaction of copper 2 ions and sodium hydroxide
Cu ( NO3)2 + 2NaOH -> 2NaO3 + Cu(OH) 2
What is the balanced symbol equation for the reaction of iron 2 ions and sodium hydroxide
Fe(NO3)2 + 2NaOH -> 2NaNO3 + Fe(OH)2
what is the balanced symbol equation for the reaction of iron 3 ions and sodium hydroxide
Fe(NO3)3 + 3NaOH -> 3NaNO3 + Fe(OH)3
describe the test to determine the carbonate ion
- Add dilute acid to sample
- if carbonate is present - the acid will react with the carbonate to make carbon dioxide gas AND Effervescence will be see
- bubble the gas through the lime water . if the lime-water goes cloudy = carbon dioxide proved = that we have started the experiment with a carbonate ion
describe the test for halide ions
- add dilute nitric acid to the sample
- add dilute silver nitrate solution
-halide ions produce a precipitate of the silver halide - each halide makes a different coloured precipitate
what colour precipitate is formed from chloride ions
white precipitate of silver chloride
what colour precipitate is formed from bromide ions
cream precipitate of silver bromide
what colour precipitate is formed from iodide ions
- yellow precipitate of silver iodide
describe the test to determine the sulfate ion
- Add dilute hydrochloric acid to our sample
- Add barium chloride solution
- If sulfate ions are present, there will be a white precipitate present
what is flame emission spectroscopy
an instrumental method used to analyse metal ions in solutions.
what is the process to carrying out flame tests
1) dip a nichrome wire loop into hydrochloric acid, and heat it in a flame, to clean off any excess chemicals that are on it
2) dip it into the acid again, then dip the loop into the metal compound that is being tested
3) hold the loop in a roaring blue bunsen burner flame
4) use the colour of the bunsen flame to identify the metal ion in the compound
what are the problems with flame test
- the colour of the flame test can be difficult to distinguish
- this is especially true, if there is only a low concentration of the metal compound
- sometimes, a sample contains a mixture of ions, which can mask the colour of the flame
- so instead of doing flame tests, scientists use flame emission spectroscopy
how does the flame emission spectroscopy method work
- a sample of the metal ion in a solution is placed into a flame
- the light given out is passed into a machine, called a spectroscope
- the spectroscope converts the light into a line spectrum
- the positions of the lines in the spectrum are specific for a given metal ion
- this can be used to identify the metal ion
- it can also identify the concentration of the metal ion, as the light becomes more intense with higher concentrations
what are the advantages of instrumental methods
- they are quicker than flame tests
- they are senstive, meaning flame emission spectroscopy can work even on a tiny sample of a metal compound
- therefore, they allow very small samples to be analysed
- they are highly accurate, and is more likely to identify a metal ion correctly and quickly
- if a samples contains multiple metal ions the spectrum will show the lines for all of them
what are disadvantages of instrumental methods
- the equipment is usually very expensive
- it takes special training to use
- it gives results that can often only be interpretated by comparison with data from known substances
