Testing for metal ions
Dilute sodium hydroxide solution is used in tests for some Shiny element that is a good conductor of electricity and heat, and which forms basic oxides. Electrically charged particle, formed when an atom or molecule gains or loses electrons. in A substance formed by the chemical union of two or more elements..
Testing for metals
Dilute sodium hydroxide solution reacts with some metal ions in solution, forming metal hydroxides. Some of these metal hydroxides are Unable to dissolve in a particular solvent. For example, sand is insoluble in water., so they appear as A suspension of particles in a liquid formed when a dissolved substance reacts to form an insoluble substance, eg in a precipitation reaction.. For example, copper sulfate Mixture formed by a solute and a solvent. reacts with a few drops of sodium hydroxide solution:
copper sulfate + sodium hydroxide \(\rightarrow\) sodium sulfate + copper hydroxide
CuSO4(aq) + 2NaOH(aq) \(\rightarrow\) Na2SO4(aq) + Cu(OH)2(s)
Copper hydroxide forms a blue precipitate.
| Metal ion | Precipitate colour |
| Zinc, Zn2+ | White |
| Calcium, Ca2+ | White |
| Copper, Cu2+ | Blue |
| Iron(II), Fe2+ | Green |
| Iron(III), Fe3+ | Brown |
| Metal ion | Zinc, Zn2+ |
|---|---|
| Precipitate colour | White |
| Metal ion | Calcium, Ca2+ |
|---|---|
| Precipitate colour | White |
| Metal ion | Copper, Cu2+ |
|---|---|
| Precipitate colour | Blue |
| Metal ion | Iron(II), Fe2+ |
|---|---|
| Precipitate colour | Green |
| Metal ion | Iron(III), Fe3+ |
|---|---|
| Precipitate colour | Brown |
Distinguishing between zinc ions and calcium ions
A few drops of dilute sodium hydroxide solution react to form a white precipitate with zinc ions and with calcium ions. However, if In chemistry, a substance is in excess if there is more than enough of it to react with another reactant. sodium hydroxide solution is added:
- the zinc hydroxide precipitate When a substance breaks up and mixes completely with a solvent to produce a solution. to form a colourless solution
- the calcium hydroxide precipitate is unchanged
Question
A green precipitate forms when dilute sodium hydroxide solution is added to a sample in solution. Identify the metal ion present in the original solution.
Iron(II) ions, Fe2+, are present.