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Syllabus
Syllabus
Sodium Hydroxide solution can be used to identify some metal ions (cations).
Solutions of Aluminium, Calcium and Magnesium ions form white precipitates when Sodium Hydroxide solution is added but only the Aluminium Hydroxide precipitate dissolves in excess Sodium Hydroxide solution.Solutions of Copper(II), Iron(II) and Iron(III) ions form coloured precipitates with Sodium Hydroxide
Copper(II) forms a blue precipitate, Iron(II) a green precipitate and Iron(III) a brown precipitate.
Students should be able to write balanced equations for reactions producing insoluble hydroxides.
Students are not expected to write equations for the production of Sodium Aluminate.
What does this mean?
What does this mean?
Precipitation with Sodium Hydroxide
Precipitation with Sodium Hydroxide
All dissolved metal ions from the Transition Block of the Periodic Table precipitate with Sodium Hydroxide, as do most Group 2 metals and Aluminium.
A precipitate may form when two soluble ionic substances are mixed.
In a solution the anions and cations are split up, so the anion from one solution will sometimes collide with the cation from the other.
If they happen to form an insoluble substance it will fall to the bottom of the test tube.
Iron (II), Iron (III) and Copper (II)
Iron (II), Iron (III) and Copper (II)
Transition metal hydroxides are all insoluble and colourful, so this is a good way to identify the metal ion that was dissolved.
Generally:
Mx+(aq) + xOH-(aq) --> M(OH)x(s)
Copper (II):
Cu2+(aq) + 2OH-(aq) --> Cu(OH)2(s) Blue Precipitate
Iron (II):
Fe2+(aq) + 2OH-(aq) --> Fe(OH)2(s) Green Precipitate
Iron (III):
Fe3+(aq) + 3OH-(aq) --> Fe(OH)3(s) Brown Precipitate
Iron (II) left.
Iron (III) 2nd left.
Copper (II) 2nd right
The remaining precipitate is for Chromium ions which are not part of the GCSE syllabus.
Aluminium, Calcium And Magnesium.
Aluminium, Calcium And Magnesium.
Only tranistion metals ions tend to form colourful precipitates.
So all three of these metals ions form white precipitates.
Calcium:
Ca2+(aq) + 2OH-(aq) --> Ca(OH)2(s) White Precipitate
Magnesium :
Mg2+(aq) + 2OH-(aq) --> Mg(OH)2(s) White Precipitate
Aluminium:
Al3+(aq) + + 3OH-(aq) --> Al(OH)3(s) White Precipitate
This isn't much of a test, but if we add more Sodium Hydroxide only the Aluminium Precipitate dissolves.
Videos
Videos
Copper (II) test
Copper (II) test
Iron (II) test
Iron (II) test
Iron (III) Test
Iron (III) Test
All of the above in one exciting video
All of the above in one exciting video
PAST PAPER QUESTIONS
PAST PAPER QUESTIONS
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