Chemical elements
    History of Iron
    Physical Properties
    Chemical Properties
    Iron Salts
    PDB 101m-1aeb
    PDB 1aed-1awd
    PDB 1awp-1beq
    PDB 1bes-1c53
    PDB 1c6o-1ci6
    PDB 1cie-1cry
    PDB 1csu-1dfx
    PDB 1dgb-1dry
    PDB 1ds1-1e08
    PDB 1e0z-1ehj
    PDB 1ehk-1f5o
    PDB 1f5p-1fnp
    PDB 1fnq-1fzi
    PDB 1g08-1gnl
    PDB 1gnt-1h43
    PDB 1h44-1hdb
    PDB 1hds-1i5u
    PDB 1i6d-1iwh
    PDB 1iwi-1jgx
    PDB 1jgy-1k2o
    PDB 1k2r-1kw6
    PDB 1kw8-1lj0
    PDB 1lj1-1m2m
    PDB 1m34-1mko
    PDB 1mkq-1mun
    PDB 1muy-1n9x
    PDB 1naz-1nx4
    PDB 1nx7-1ofe
    PDB 1off-1p3t
    PDB 1p3u-1pmb
    PDB 1po3-1qmq
    PDB 1qn0-1ra0
    PDB 1ra5-1rxg
    PDB 1ry5-1smi
    PDB 1smj-1t71
    PDB 1t85-1u8v
    PDB 1u9m-1uyu
    PDB 1uzr-1vxf
    PDB 1vxg-1wri
    PDB 1wtf-1xlq
    PDB 1xm8-1y4r
    PDB 1y4t-1ygd
    PDB 1yge-1z01
    PDB 1z02-2a9e
    PDB 2aa1-2azq
    PDB 2b0z-2boz
    PDB 2bpb-2ca3
    PDB 2ca4-2cz7
    PDB 2czs-2dyr
    PDB 2dys-2ewk
    PDB 2ewu-2fwl
    PDB 2fwt-2gl3
    PDB 2gln-2hhb
    PDB 2hhd-2ibn
    PDB 2ibz-2jb8
    PDB 2jbl-2mgh
    PDB 2mgi-2o01
    PDB 2o08-2ozy
    PDB 2p0b-2q0i
    PDB 2q0j-2r1h
    PDB 2r1k-2spm
    PDB 2spn-2vbd
    PDB 2vbp-2vzb
    PDB 2vzm-2wiv
    PDB 2wiy-2xj5
    PDB 2xj6-2ylj
    PDB 2yrs-2zon
    PDB 2zoo-3a17
    PDB 3a18-3aes
    PDB 3aet-3bnd
    PDB 3bne-3cir
    PDB 3ciu-3dax
    PDB 3dbg-3e1p
    PDB 3e1q-3eh4
    PDB 3eh5-3fll
    PDB 3fm1-3gas
    PDB 3gb4-3h57
    PDB 3h58-3hrw
    PDB 3hsn-3ir6
    PDB 3ir7-3k9y
    PDB 3k9z-3l4p
    PDB 3l61-3lxi
    PDB 3lyq-3mm8
    PDB 3mm9-3n62
    PDB 3n63-3nlo
    PDB 3nlp-3o0f
    PDB 3o0r-3p6o
    PDB 3p6p-3prq
    PDB 3prr-3sel
    PDB 3sik-3una
    PDB 3unc-4blc
    PDB 4cat-4erg
    PDB 4erm-4nse
    PDB 4pah-8cat
    PDB 8cpp-9nse

Detection of Iron

Iron readily lends itself both to detection and estimation. In this chapter the more important methods of detecting and estimating iron in its compounds are discussed.

Detection of Iron by Dry Tests

Iron salts, when moistened with hydrochloric acid and heated on a loop of platinum wire in a Bunsen flame, emit a shower of sparks. When heated on charcoal with sodium carbonate in the blowpipe flame, the compound is converted into a dark-coloured residue. If potassium cyanide is added to the sodium carbonate and iron compound, and the whole heated on charcoal in the inner flame of the blow-pipe, metallic iron is obtained as a grey, magnetic powder.

If a little of the iron compound is heated with borax on platinum wire in the outer blow-pipe flame, on cooling, a yellow transparent bead is obtained, which becomes bottle-green upon heating in the inner or reducing flame of the blow-pipe, in consequence of reduction to the ferrous condition.

Detection of Iron by Wet Tests

The presence of iron in solution may readily be detected by a considerable number of sensitive reactions. Thus ferrous iron gives a green precipitate of ferrous hydroxide upon addition of excess of ammonium hydroxide. With potassium ferricyanide and a trace of acid, a deep blue precipitate - Turnbull's blue - is obtained. With potassium ferrocyanide a white precipitate is obtained in the entire absence of any ferric salt. Ferric iron, on the other hand, is usually characterised by its deep yellow or brown colour. Addition of concentrated hydrochloric acid deepens the colour. With excess of ammonium hydroxide, brown flocculent ferric hydroxide is precipitated. With potassium ferrocyanide solution, a deep blue colour is obtained in acid solution, whilst with potassium ferricyanide there is no action. Potassium thiocyanate gives in acid solution a deep red colour, which is not destroyed by heat. Salicylic acid gives a violet colour, provided no free mineral acid is present.

It is usual, in systematic qualitative analysis, to remove silver, lead, and mercury from the solution to be analysed, by precipitation as chlorides on addition of hydrochloric acid. The metals capable of precipitation as sulphides with hydrogen sulphide in acid solution are next removed, and the filtrate, boiled to expel any dissolved hydrogen sulphide, is treated with ammonium chloride and excess of ammonium hydroxide. In the absence of phosphates, the precipitate may contain the hydroxides of iron, aluminium, and chromium. The presence of iron is evidenced by the brown colour, if the metal is in the ferric condition. In any case, the precipitate is treated with sodium peroxide and water, whereby any aluminium is dissolved as sodium aluminate, any chromium as sodium chromate, the iron remaining as insoluble ferric hydroxide. If desired, a confirmatory test may be applied. For example, the precipitate may be dissolved in hydrochloric acid and potassium ferrocyanide added. The characteristic blue colour indicates iron.

If a phosphate was present, the precipitate obtained on addition of ammonium chloride and hydroxide may contain phosphates of such metals as calcium, etc., which are normally precipitated in later groups in systematic analysis. The precipitate is therefore dissolved in dilute hydrochloric acid, and the solution nearly neutralised with sodium carbonate. Sodium acetate is now added, and the whole boiled. The precipitate contains the phosphates of aluminium, chromium, and iron, and is treated, as already indicated, with sodium peroxide and water.
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