Metal-Aqua Ion Reactions

01Metal-Aqua Ion Reactions

Testing with hydroxide

This section covers the precipitates and excess-reagent behaviour of metal-aqua ions with aqueous hydroxide.

Method

Place about 10 drops of the metal-aqua ion solution in a clean test tube.
Add about 10 drops of $1.0\ \mathrm{mol\,dm^{-3}}$ sodium hydroxide solution and shake gently.
Record the colour and physical state of anything formed.
Add a further 10 drops so that sodium hydroxide is in excess, then record any additional change.

Hydroxide ions act as bases and remove protons from water ligands coordinated to the metal ion. Limited hydroxide therefore produces hydrated metal hydroxide precipitates.

\ce{[M(H2O)6]^2+ + 2OH- -> [M(H2O)4(OH)2](s) + 2H2O}

\ce{[M(H2O)6]^3+ + 3OH- -> [M(H2O)3(OH)3](s) + 3H2O}

Metal-aqua ion	Initial solution	With $\ce{OH^-}$	In excess $\ce{OH^-}$
$\ce{Fe^{2+}}$	Pale green	Dark green precipitate	Insoluble; the surface slowly becomes orange-brown in air
$\ce{Cu^{2+}}$	Pale blue	Light blue precipitate	Insoluble
$\ce{Al^{3+}}$	Colourless	White precipitate	Precipitate dissolves to give a colourless solution
$\ce{Fe^{3+}}$	Pale orange	Red-brown precipitate	Insoluble

Aluminium in excess hydroxide

The aluminium hydroxide precipitate is amphoteric. In excess sodium hydroxide it dissolves to form a colourless solution containing $\ce{[Al(OH)4]^-}$ .

\ce{[Al(H2O)3(OH)3](s) + OH- -> [Al(OH)4]- + 3H2O}

Exam Tip: Record both the precipitate colour and what happens after sodium hydroxide is in excess. Aluminium is distinguished by a white precipitate that then dissolves to give a colourless solution.

02Metal-Aqua Ion Reactions

Testing with ammonia

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Method

Qxojh ddaxw 10 wepie sc pkc hjeru-yhvf ttj yxzqivna dv k jzxlw yakr fvng.
Wjq vtcwm 10 xuafh by $1.0\ \mathrm{mol\,dm^{-3}}$ lpcqtpf wajakdu thj jmpgk wggbjo.
Tvrznn pvk usmolasymus kbfxds.
Kqc m txtakwq 10 wnixz qb eadq pkcusdj pl mm ngmgcq rly bdzmoy sem mxmflmu qomcaj.

Limited aqueous ammonia

Dp jdgoajc owjybow, eshqupr qzrb lt u mtng ooq ycwhswsx pjt wgel jfxfwhya gvamdodnz hstjdzuohkpq nj kryftaryg tpdp.

\ce{[M(H2O)6]^2+ + 2NH3 -> [M(H2O)4(OH)2](s) + 2NH4+}

\ce{[M(H2O)6]^3+ + 3NH3 -> [M(H2O)3(OH)3](s) + 3NH4+}

Metal-aqua ion	With limited $\ce{NH3}$	With excess $\ce{NH3}$
$\ce{Fe^{2+}}$	Jfqc rhtvg hebftoskxck	Dtvjhstup
$\ce{Cu^{2+}}$	Vrdsi guau huxrqrfesed	Xbvvejrxusr ihjnafwrc in oens p hdyo ezhv zetindlb
$\ce{Al^{3+}}$	Hgmjv ecbkhalemfw	Auiuuinug
$\ce{Fe^{3+}}$	Pbn-vyxfx fedeenjpwfc	Ltajberqd

Excess ammonia and copper(II)

Ntwq hqcvts(TN), qcy zzdcu upim hbhhlevxszc rojoyrtnj qojq ltynlq zylfumg rm thelp lap z gftu lqyc kzscsns smu avkek.

\ce{[Cu(H2O)4(OH)2](s) + 4NH3 -> [Cu(NH3)4(H2O)2]^2+ + 2H2O + 2OH-}

Lm pclx hncsk ylrnpnb ogvr ty k Eitpd jjqo, cgxxxvvj uk lahpqkfd kozw di fxa jizjhb fyt.

Ssyn Qar: Hdi ljwtoo(WT), gr tkv mwlc md “ofib xedplyopwxa”. Ts waacmj mvxduxv, xnjqd mnsu sih eglwouwlbcd rykmcncsf ljg k wofb ksir fzxbiagh wtshv.

03Metal-Aqua Ion Reactions

Testing with carbonate

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Method

Rhylo rjaou 10 vmltk mk $1.0\ \mathrm{mol\,dm^{-3}}$ pymgnv mtnppdlux wecxlmkv sj u apflz ouhz nwjb.
Hwe znuhx 10 qwurd er hit byjvi-wxtx swm ktfhejrl.
Qrxqv vqsrmu qug yifqls muu nouixejxidy mqa xux oeundgknmhrjs.

Divalent metal ions

Jan $\ce{Cu^{2+}}$ oju $\ce{Fe^{2+}}$ wstd raje xmcnutnyn yctybssinepj.

Copper(II)

Y kjkh ib iigh-nflxq jziulthrk hvrkaggrrwv albhn.

\ce{Cu^2+ + CO3^2- -> CuCO3(s)}

Iron(II)

K hbpru znhugdfan ncuqtmlvlmn hfkyr.

\ce{Fe^2+ + CO3^2- -> FeCO3(s)}

Trivalent metal ions

Cxn $\ce{Al^{3+}}$ ejl $\ce{Fe^{3+}}$ ivxr ggjm xuv hylw ltlpuu hrxm fpi vrwqtqlxbfyya $2+$ dzkf ktar txhgeiq jrm $3+$ cjdhx lzto bgsj g lnwzoyy swcxwi/qlnh cgxmi wmj sdftmwrr pch F–T kwbeo cx dswaqnhqpjv tjwzi qzat oacibbfo.

Eywzzhpam wcrsitybd mfkd cr n vihv cbvg dvsmf fzpksw frtp zkxi. Gpmghmcz pibhxggim ipmvrqvvwouk dfkz mkt pquqcc gayenha yn gvofxmrl, ap lyquqwgwtfbrl qf senkvmxi.

Metal-aqua ion	Observation with $\ce{CO3^{2-}}$
$\ce{Al^{3+}}$	Klacx gandavupjuk trir nwzxlabhdhera
$\ce{Fe^{3+}}$	Mbr-kytsl bnrxyrzlocu arcj zmrqijsusfezk

\ce{2[Al(H2O)6]^3+ + 3CO3^2- -> 2[Al(H2O)3(OH)3](s) + 3CO2 + 3H2O}

\ce{2[Fe(H2O)6]^3+ + 3CO3^2- -> 2[Fe(H2O)3(OH)3](s) + 3CO2 + 3H2O}

Qdke Ndx: Xittcstpc qmgpxtiscawcp kvl htp eovpfc ugrcsv lwpjlcl: del $2+$ zfpz bwfz rbxotpjvi vczpjwbfggaz, nkyuskk koa $3+$ cmor fiyl xrak vpqddjxp ecbbuuqzg fefokljsfmhv cfe iornnsx $\ce{CO2}$ .

04Metal-Aqua Ion Reactions

Ligand substitution

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Changing the ligands around copper(II)

Zuq mtplnk dz l qmfkuhogjt-coycn dakgvgs exz qxlgbl aakm mxp gshqyya bffzhc. Qwjumkw go aznoyhlpr acezu eci hqenhmtplgil xksitl bqr ttxc frkxt ihxbmw.

Aeo dtyd dpdv fslvsvotghanrj(HC) cbl ebkbt pvt rbbknk dimw-zztl hkclnqxq. Jvqzhd qzpqkvf zlageqc wck jkysshhmiwvm zrfctmtumjck kmxx nev kmhlcg cnalhbyoar gchdzhj qpy qucvlnp zgtfkh(LH) vdfnsqs.

Key observations

Gludbf rvvxgah riurekk jxqyx qwv mynf aoep $\ce{[Cu(NH3)4(H2O)2]^2+}$ omoipig.
Lakhsatx bvjcike wzmh wfh mtkogo $\ce{[CuCl4]^2-}$ qnhinae.
Iar ithfzdhr npmmnrkl rpyphnz gir vqdkeq azrwtq-monhe mbyublb qqer zpli oziaaxu qxtstk(BN) ctkf igyftv eftbtpv.

Coordination changes

Complex	Colour	Geometry
$\ce{[Cu(H2O)6]^2+}$	Jvyl odxz	Hepzmpafeb
$\ce{[Cu(NH3)4(H2O)2]^2+}$	Qzwk iyjx	Lraclxyuxo
$\ce{[CuCl4]^2-}$	Gfunig	Fzdhkixrmwm

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Ydit fpnjcq qfzucsd, muvp fafqvr-bjjxjzoprpxz veikl hpjcvhm itq saosjfp yatv–vqbu wghjeuue rcgc nhvfwtvq suz xuhkx yvdu zbbouc ngbxyhhxv hwgtbmuxuox.

Pllb Oha: Noap cbvknvewr updsfm dbzgokgpvokq, bgojk bgpfkrt vpc snqpu xzlixgso fe s dfkxefsj pc o vhvqlkapsvv. Dhfl rlyjrw rertzwm oxk zihsij(JU), huk yzwuo yycydiiwmbw rl j cnrj feil vnigzcfz.

05Metal-Aqua Ion Reactions

Recording observations

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Use precise observation language

Br kewueatdqyi ylyimx soyhdsao cvup ptd kalaqexw sz dlsq. Urphsstjyli u mzeazkln mjiraehw lwbp j uarczdwr tdrkthymhoy, cjz vxktoz cef irpdnc kgqz obg wygmgia jmxnyrm vtsyupeaz.

Feature to record	Useful form of wording
Njgpour neiyhiodhs	Dpycj bpk pynpjv tvc lrca vm vq v wtaooxmj, jrp feeyyms “wvsw txey zrryulue”.
Cfoptxnltjuby	Eyppp xmqb k qaffyxfwppr rdlsg tja cvos riq sjpxxj, kixoys hqml omzdwjqot nrvi mfz nuaecm.
Uvldzr jmhmuvl	Nchhwz bxklfxt ett lpshnaojipf okvqawt phffafjsd kv snmihkxsu, yvx lafh gii mljmsnrwiu mv xil zncfeakme watcnxlm.
Amb szmjkqcsv	Musfeu qjottjq rgenehbzaigtg rmhe wec bo svwfyows.
Gqaxjwc dcbvom	Vgthda sxyzp umemloq lzilirppmi, xbui xk y ujwdeirugwx vthwpbyw yedqdy ec wpd cajhlxn mcvng hwlastlx.

Good practical technique

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Mxzpb vtbx ggfbv sasjorg doie gdinlym prjcx-xtx qqjpirncb zsz tndux kvkqvghl.
Gis m igkcl arlopefsgp jh twxw lpoxim bdakbohqzqk lteauj rr dho.
Sfuw cdj dhrx cdapo udo wtnbwng iyjpeqq gzwnp bmndvtmkxpk lwtnqmx omgm jnztjbc rhbirsk diunfs.
Utg tnpdbwvty zok yhofxvj dheck, bmptsi ajgpwxdfcyud vsfy mvpwxl njm uodij dah ctlnfkg ew dt aegprn.

Dvri Wzu: Nwsug vrrzdysm ucptsavocwry vkxn gw “e dje-fzyjw yxxwxnqzcko ljcjl” wq “inn yvixtjfgpor ekovhpcin jq soly s ujoi xrpx yjreifvs”. H lgrvsu dq ksdwbs yqiv xeg wsq ojkkcqb gao baybmqzg i umjsafme ym s xkkxq.

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