should be introduced into a roaring flame and the colour of the flame should be observed and
recorded.
Testing with NaOH:
The unknown substance that is being tested will need to firstly be made into a solution if it is
not already. If it is currently in crystal form, then the only thing that needs to do to make it a
solution is to add water.
Once the solution has been made, add some Sodium Hydroxide to it. Once this has been done,
the solution need to be observed and if any precipitate has been formed, then the colour of it
needs to be recorded.
If no precipitate is formed though, the test tube should be warmed by putting it into a test
tube holder and gently introducing it to a roaring flame. Whilst the tube is being warmed a
damp piece of red litmus paper should be held over the top of the test tube. The colour of the
litmus paper should be recorded.
Add a little Nitric Acid:
The substance need to be made into a solution form and then some Nitric Acid should be
added. As soon as the Nitric Acid is added the test tube should be observed, and if any
bubbles are given off then this should be recorded. The bubbles given off would be Carbon
Dioxide (CO2), and this could be tested by passing it through limewater.
Add a little Nitric Acid and then some Silver Nitrate:
The unknown substance firstly needs to be in solution form, and ten some Nitric Acid need to
be added. Once this has been added, and if no precipitate has been made then a few drops of
Silver Nitrate should be added to the solution as well. If a precipitate is formed then the
colour of it needs to be recorded.
Add a little Hydrochloric Acid and then some Barium Chloride:
The unknown substance firstly needs to be made into a solution form, and then some
Hydrochloric Acid should be added. Once this has been added just a few drops of Barium
Chloride should also be added, if a thick white precipitate is formed then you know that you
have Sulphate ions present in your salt solution.
Results
The results of the test are as follows:
Flame test:
If an orange flame is formed then you know that Sodium ions are present in the salt solution.
If a lilac flame is formed then you know that Potassium ions are present in the salt solution.
If a red flame is formed then you know that Calcium ions are present in the salt solution.
Testing with Sodium Hydroxide:
If a dark green precipitate is formed then you know that Iron (II) ions are present in the salt
solution.
If a rusty red/brown precipitate is formed then you know that Iron (III) ions are present in
the salt solution.
If a blue precipitate is formed then you know that Copper ions are present in the salt solution.
When the solution is warmed and tested with damp red litmus, if the litmus is to turn blue then
you know that you have Ammonium ions present.
Add a little Nitric Acid:
If carbon dioxide is given off then you know that you have a carbonate.
Add a little Nitric Acid and then some Silver Nitrate:
If a precipitate is formed then you know that you have a Group 7 element present in the
solution.
If a white precipitate is formed then you know that Chloride ions are present in the salt
solution.
If a creamy white precipitate is formed then you know that Bromide ions are present in the
salt solution.
If a yellow precipitate is formed then you know that Iodide ions are present in the salt
solution.
Add a little Hydrochloric Acid and then some Barium Chloride:
If a thick white precipitate is formed then you know that Sulphate ions are present in the salt
solution.
Test P Q R S T
Start Appearance Creamy Crystals Green/blue crystals White Crystals Clear solution
Transparent yellow solution
Flame Lilac Dark Green Orange Light Green Orange Sparks
NaOH No precipitate A thick blue precipitate was formed. No precipitate No precipitate Thick
brown precipitate formed
NO3 Nothing happened Gas given off Nothing happened Nothing happened Nothing happened
Litmus Paper Stayed red Stayed red Turned purple Turned blue Stayed red
AgNO3 Creamy precipitate formed No precipitate Creamy precipitate formed White
precipitate formed White precipitate formed
BaCl2 No precipitate No precipitate No precipitate White precipitate formed No precipitate
Conclusion Potassium Bromide Copper Carbonate Sodium Bromide Ammonium Sulphate Iron
(III) Chloride
Conclusion
Solution P:
When the solution was first introduced into the flame, a very faint lilac flame was produced,
but the longer it was in the brighter the flame got.
When it was added to the Silver Nitrate, the precipitate formed was not very thick, but it was
in between yellow and creamy white. This caused slight problems as this meant the solution
could have either contained Bromide or Iodide. I finally thought that it must be Bromide after
comparing the colour with other creams and yellows. I also thought that as the crystals
originally started off creamy, and the unknown solution was therefore creamy to start, that if
the precipitate was supposed to be yellow it should have been a far deeper and more
pronounced yellow.
From all of these tests I concluded that the salt must be Potassium Bromide or KBr.
Solution Q:
The start colour of the unknown crystals were greeny blue which gave an indication that it
could contain Copper ions, however to make sure that this was correct the flame test and the
testing with Sodium Hydroxide could ensure this early prediction.
The flame was a prominent green colour, and this could not be doubted, this verified my
earlier thought, that the substance must contain Copper crystals. However to make absolute
certain this was correct I still added Sodium Hydroxide to the solution. When this formed a
thick blue precipitate I was absolutely certain the substance contained Copper ions.
When the Nitric Acid was added to the solution, bubbles immediately and vigorously fizzed
off, which gave the indication that the solution was a carbonate.
From all of these tests I concluded that the salt must be Copper Carbonate or Cu2CO3.
Solution R:
When the solution was introduced to the roaring flame, the flame turned orange. This however
may not be considered as a change in colour as when only the wire with no solution is
introduced into the flame, the flame turns orange. If the solution had turned the flame orange
then that would mean that the solution contained Sodium ions. I carried on with the other tests
for metal ions, as I could not ensure that Sodium was the correct element. During all of the
other tests for metal ions, I got negative results so I finally concluded the metal ion must be
Sodium.
When Nitric Acid, and then Silver Nitrate were added to the solution, a fairly thin creamy
precipitate was formed. This meant that the solution contained Bromide ions.
From all of these tests I concluded that the salt must be Sodium Bromide or NaBr.
Solution S:
When the solution was introduced into the roaring flame a faint green flame was produced,
this led me to believe that the solution contained Copper ions. However when just the wire was
added without any solution on it as a control, the flame still changed to a slight green one.
When this happened I thought that the wire must be dirty, so I cleaned it in Hydrochloric
Acid. Even after cleaning the wire, it still turned slightly green. From this I concluded that it
was probably not the solution that contained Copper ions, but instead it was probably the wire
that was made of Copper.
When then testing the solution with Sodium Hydroxide, no precipitate was formed. This gave
even stronger evidence to say that the solution did not contain Copper ions, because if it did a
blue precipitate would have been formed.
When I then tested the solution with Nitric Acid, I still got no result, however when damp red
litmus was held at the top of the test tube, and the test tube was heated, the litmus went blue
fairly quickly. This is excellent proof that the solution contained Ammonium ions.
When Hydrochloric Acid and Barium Chloride were added to the solution a fairly thick white
solution was formed which meant that the solution had to contain Sulphate ions.
From all of these tests I concluded that the salt must be Ammonium Sulphate or (NH4)2SO4.
Solution T:
When the solution was introduced to the flame, bright orange sparks flew off of the end of
the wire. The flame however did not change colour which did not indicate that there was any
particular metal ion present.
When adding Sodium Hydroxide to the solution, the solution immediately formed a very thick
brown precipitate which gave strong indication that the solution contained Iron (III) ions.
When adding Nitric Acid to the solution, to test for Carbonate ions, nothing happened so I
went onto the next test which was to add Silver Nitrate and Nitric Acid. Being as nothing had
happened when I had added just Nitric Acid, I added some Silver Nitrate to that same test
tube. This produced a white precipitate to indicate that the solution contained Chloride ions.
From all of these tests I concluded that the salt must be Iron (III) Chloride or FeCl3.
Evaluation
This experiment could be made better by ensuring that the white, creamy white and yellow
precipitates for the Nitric Acid and Silver Nitrate test are the right colour. This could involve
colour charts to ensure that you do not mistake creamy white for white.
Further experiment that could be carried out as an extension from this one could be to test
further salt solutions to discover what they are, or you could test more complex salts to see
what ions are present in them. This could also include other further experimentation to see if
other elements cause different results for any of the tests, or to see if any other tests give
accurate results.
