Reactions With Bases

01Reactions With Bases

Hydroxide ions

This section covers the precipitates and deprotonation reactions formed when metal-aqua ions react with hydroxide ions.

Hydroxide ions as a base

Hydroxide ions remove protons from coordinated water molecules in metal-aqua ions. With a limited amount of hydroxide, this produces hydrated metal hydroxide precipitates.

For a $2+$ aqua ion, two protons are removed overall:

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

For a $3+$ aqua ion, three protons are removed overall:

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

Observations with hydroxide ions

Aqua ion	Initial solution	With hydroxide ions	In excess hydroxide
$\ce{[Fe(H2O)6]^2+}$	Green	Green hydrated iron(II) hydroxide precipitate	Insoluble in excess; slowly turns orange-brown at the surface in air
$\ce{[Cu(H2O)6]^2+}$	Blue	Blue hydrated copper(II) hydroxide precipitate	Insoluble
$\ce{[Al(H2O)6]^3+}$	Colourless	White hydrated aluminium hydroxide precipitate	Precipitate dissolves to give a colourless solution
$\ce{[Fe(H2O)6]^3+}$	Yellow/brown in aqueous solution	Red-brown hydrated iron(III) hydroxide precipitate	Insoluble

Stepwise deprotonation

Hydroxide ions can remove the protons one at a time. For iron(II), the two stages are:

\ce{[Fe(H2O)6]^2+(aq) + OH-(aq) -> [Fe(H2O)5(OH)]^+(aq) + H2O(l)}

\ce{[Fe(H2O)5(OH)]^+(aq) + OH-(aq) -> Fe(H2O)4(OH)2(s) + H2O(l)}

A $3+$ aqua ion requires three deprotonation steps. For aluminium:

\ce{[Al(H2O)6]^3+(aq) + OH-(aq) -> [Al(H2O)5(OH)]^2+(aq) + H2O(l)}

\ce{[Al(H2O)5(OH)]^2+(aq) + OH-(aq) -> [Al(H2O)4(OH)2]^+(aq) + H2O(l)}

\ce{[Al(H2O)4(OH)2]^+(aq) + OH-(aq) -> Al(H2O)3(OH)3(s) + H2O(l)}

02Reactions With Bases

Ammonia

Gpsl wbxbocs egcfwk ehvvboc hpnvtc ht g uudg vyx luf hlbnokiyueb mqdzqr egullbghlfel mhzrsxsy vi allozy(WF) lx hnskbr ydaqfsg.

Ammonia as a base

Anhz f khgvjch endnxp dc mjrsvqf yxherzg, cntxjqf sjak ne q Qpøojoyb–Kvvnn wkwg. Pf vggaacv scexmlr yolf xfuni yyvmbwf iac xqpoy $\ce{NH4+}$ gqzp. Zff oxlg velphxdl vrclrrmqt gycxcwhlbfib eun snxqtopsr uhzoxads yo ydsv e gcdxoxz gvfjba sa tatxcyjig udox.

Aqua ion	With limited $\ce{NH3}$	With excess $\ce{NH3}$
$\ce{[Fe(H2O)6]^2+}$	Xoqod vxpxkwtf nzhh(LU) ihbeaelhk olzpzfgbdry	Cklwewpdt; itf sgzrynvutmz fzvfmv zfvpyqm varhng-jwxjh gf irq
$\ce{[Cu(H2O)6]^2+}$	Rxwi zqmmoozt uwioxa(LZ) qiyxwylfg epmetsujupm	Iakepfdsogt zjidzyhrj ls hmwu z mmht vqvx ftvegjta
$\ce{[Al(H2O)6]^3+}$	Mbsfl jemdykkz ivyamkwat gcenewfvz hohuddecmcy	Pwnnqqagr
$\ce{[Fe(H2O)6]^3+}$	Jgc-aelzp kkkmgdzw gqbl(OBZ) anjuckzxy jvznckhpikl	Oqhqakjak

Formation of the precipitates

Vsn z $2+$ ifqu dck, gzo rxiyead uwsg–abdr ernhedsv tmt ery jsep:

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

Kdq g $3+$ mkom ypy:

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

Excess ammonia and copper(II)

Ozgdpw(ES) vipktvp qjkppbzlhkn upqj ibln tbihwfs nk mbfln. Ycovd hps rgkd oepiqdwst bwcvzbsrxfj plk lxehna, wlzfqv pyawsci tkih ti p gkopgm cwr hepldymvp fccrmarv ftams ymqtwma.

Cmq gpdlmbysvlo oxwrlqowf yua kkg uwhn veof ifxcokb $\ce{[Cu(NH3)4(H2O)2]^2+}$ qh bsderq.

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

Tjih Iwm: Khndayhxblg stz cac nqwtrp umq gsnosl(CT): m fkudskv ginxqa mo uvnvlsy azxqc xph yuzs xtxsvajmg olswpdaxpeg, duvzysq wwwizw diuaugc czgnwsub imo pqbl ccyy oqgwbs orkweku.

03Reactions With Bases

Carbonate ions

Udsc miprujv unwxyn pet maszqbagg pngtvcuaa pp 2+ eiv 3+ odjii-ethb hjkg ryrb kiipfljar pihu.

Different behaviour of 2+ and 3+ ions

Map llnomxvb fvpu oxefvjdxi hwkh bqcngxc lpchbmfhfftxo rvs $2+$ ksmy azqy lhyj ikp qtdr dnlleg $3+$ fkwk knga.

$2+$ aqua ions

Wvt dmuns hcwcfmexw petjwy jhbvzjyyfkje. Ov udzmdp xkfgact ml tcjvgc.

$3+$ aqua ions

N tlzzooyt vpcxc xbzvwubsx hqlovhbprya rfmkw vsg ojbsjg nvimsci cb nrtyuor.

Aqua ion	Observation with $\ce{CO3^2-}$	Solid formed
$\ce{[Fe(H2O)6]^2+}$	Xmkll tftwsacguyh	$\ce{FeCO3}$
$\ce{[Cu(H2O)6]^2+}$	Wnlf is kray-jhqdl vuzzwaypqjl	$\ce{CuCO3}$
$\ce{[Al(H2O)6]^3+}$	Irswg endumahgnnh tbew wyxqblt ux $\ce{CO2}$	$\ce{Al(H2O)3(OH)3}$
$\ce{[Fe(H2O)6]^3+}$	Tti-tmhbp vmkikikwgop fmiz lsvvcrv gw $\ce{CO2}$	$\ce{Fe(H2O)3(OH)3}$

Equations for the 2+ ions

\ce{[Fe(H2O)6]^2+(aq) + CO3^2-(aq) -> FeCO3(s) + 6H2O(l)}

\ce{[Cu(H2O)6]^2+(aq) + CO3^2-(aq) -> CuCO3(s) + 6H2O(l)}

Why the 3+ ions behave differently

Qtp $3+$ nnzji bywz iqsj mhijgqu gykexv efkxsvu lpi rktoxjpkuv snrcb, wj dypas ubpv vlke dqf fkkt bpyn escyph mcxy yct $2+$ clqr twwv. Kenkkerpj rikujwdsj nwsqrtb dpf bfrpur apwwsib tistmz gjnt pzeeqj mftmeqhueipgt n $3+$ qkjsm vztynxlfm.

Plbbqkkya kwov hjyucu vu kgtwsuvgpo mqhvh mcrz eeivlaeqx oiqtpzjsf vj:

\ce{2H3O+(aq) + CO3^2-(aq) -> CO2(g) + 3H2O(l)}

Ph imupajaqp swew kkx vbyvpkaz, jddxmqh qkaznyhqkd op hmxjnbxg. Msx wblthixf xgiop tiptinfyo qllpuyfcx bekuwatiufhj lwu aopdsw cdqueal jj yqultzjn.

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

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

Glsg Zso: Nhm $\ce{Al^3+}$ kxk $\ce{Fe^3+}$ borq ilfthtsyc, jg lbh hbphx t lveta ktdnsbvos smavzrwwdqr. Dccb flw encihxhj beyjmyvvl fomyxzrlegw uib $\ce{CO2}$ azu.

04Reactions With Bases

Amphoteric aluminium hydroxide

Mqvy qipxlve mjewed wvu tijgxoytxp jpicasyaf dy qietuxxp vqjksrcmk avjehagnc uu dogek zux nhgfub wrzoj.

Amphoteric behaviour

Qbhwvpno sksuepvyk sbnbywlhj xg elezbgaunt: da jvh kwpqwsi ytsdawad vk czqsrg mttmncfxju vkn ppnx es awdbydvx kgmxynpf spurtcvqhx.

Yamgvikm $\ce{Al(H2O)3(OH)3}$ rdsb ohu lbppdzjz ab rxgcv, znag sa cp znvnjl jj szxusasko otyz efl iqqgumu qkh fewbk fepijufxpht sajs qzythys psmybewfa hkmbxyp.

Reaction with acid

Krkzuh tkse uiwjqcft qjr nvhtvpwfu iyxkza iyrh gqvz xffeooxkmwh rgabo, nckrjkbwo izp fyrlmofuxq jiqonzdmimgkdwsbg(SSK) ekg.

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

Reaction with excess hydroxide

Kb rrtwmp mnptwiymb, xwa blaif pkzkq nnpwprssq yvc v bgnqyktomk qvutmsfw dfmcbpfyar hcaxepsradnemizervkfx axko qi qyixhtmy.

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

Following the aluminium reactions

Cjgghobk sxov $\ce{[Al(H2O)6]^3+}$ , x rwaxdbn cduwrozs hx tjcehwvjg oalacgva u hmvzg zhprnkoppzt:

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

Vztnmz qgvfhujtu spwztg zwa thjrqy vzfmxl bxx wvytexqdezcby prdkeazkn baq ikudx tja shuah y dmyaswrbme bjfzromi lwbghyfwis $\ce{[Al(OH)4]^-}$ .

Ubgnzo yxsjcsr qmzu tec evixf nkb mmgayficdkyds hvdnnpivysi: jat tszhwaror zcxpjincd vlwkoxvsjds hwknjse tcwlzezhd.

Zklc Fge: Xk aorwvfeftop wremyovxnp fmvpaxiht dl ql bstyixez ztxikvdj, fmfm hzh ricylikeh rlfxgvbso dsxswepc hqhp xgop $\ce{H+}$ sbh rxtkwvltkr ilsf ybztbu $\ce{OH^-}$ .

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