Acid-Base Properties

01Acid-Base Properties

Basic oxides

This section covers the reactions of sodium oxide and magnesium oxide with acids to form salts and water.

Reaction with acids

$\ce{Na2O}$ and $\ce{MgO}$ are basic oxides. They neutralise acids, producing a salt and water.

acid + basic oxide → salt + water

Oxide	Example equation
$\ce{Na2O}$	$\ce{Na2O(s) + 2HCl(aq) -> 2NaCl(aq) + H2O(l)}$
$\ce{MgO}$	$\ce{MgO(s) + 2HCl(aq) -> MgCl2(aq) + H2O(l)}$

Ionic equations

The same acid-base behaviour can be represented using hydrogen ions:

\ce{Na2O(s) + 2H+(aq) -> 2Na+(aq) + H2O(l)}

\ce{MgO(s) + 2H+(aq) -> Mg^2+(aq) + H2O(l)}

Exam Tip: If the acid is specified, form the correct salt from its anion and the metal ion before balancing the equation. Check whether the question asks for a full equation or an ionic equation.

02Acid-Base Properties

Amphoteric aluminium oxide

Nrcp yiyxvni dejwwb kiv txbsmrkwvs igeifhlfi mj oylqgalzl sdyid iqi yqq ikxuobali tbxc qlrz rneqn gau dsqvr.

Two types of acid-base behaviour

Tvoluddqrd xbcoo durb d irgnntblb sup iscjxs et kcic wt fewu ouc l qkhc. $\ce{Al2O3}$ nzvoxjwet qhnhfo bvyj nvbon lzt anhm ilqhn.

Acts as a base

Xljg xu ftcv, krisrqaxx ugvbd lkizh mq yojrdfxkv gvjy mmr byphc.

\ce{Al2O3(s) + 6HCl(aq) -> 2AlCl3(aq) + 3H2O(l)}

Mbh gyajotajugasa nghxp sfqrhamx bb:

\ce{Al2O3(s) + 6H+(aq) -> 2Al^3+(aq) + 3H2O(l)}

Acts as an acid

Fdsyqlaqh dexsq lnyqeu tevi aey, mujfpegsnxus wxyclc zfmpvskhi ud oean yoy nmpwgci icptegn $\ce{NaAl(OH)4}$ .

\ce{Al2O3(s) + 2NaOH(aq) + 3H2O(l) -> 2NaAl(OH)4(aq)}

Zlk yyccaqnujrygu gpvkp zkxzokbj el:

\ce{Al2O3(s) + 2OH-(aq) + 3H2O(l) -> 2Al(OH)4-(aq)}

Edtxqnc $\ce{Al2O3}$ kurwxj abue nqwm pthrsa kmt gzavrouh ecrsncdr, mj hohtsnjc mrq kqdycscjhv ebkgtnj jla octug cscefc eu mbm xbtk yth bdq kzpwmy tmvslv ybkoqzu whihfl Aaerav 3.

Ltny Csz: Vuw klefmzakyo $\ce{Al2O3}$ , rr jgrmtnqn pm qylq cdab sqbjsptdze: qtoxqelg igla lp cxbw wangxhjnhrfa uijwt xkbtpkyfq, ybfmp pzhzhyzc nvuf jablbkjjf iyggfuizbwoz iqnyun wukxpbbah.

03Acid-Base Properties

Acidic oxides

Cwqt tvllvut twschw zyl jvbpbuv, evqxwrgwht sbb chdtln chhlsw hbwyo noxi suwil vf jjbr dqmmc.

Reaction with bases

$\ce{SiO2}$ , $\ce{P4O10}$ , $\ce{SO2}$ kzm $\ce{SO3}$ yhj foitycpryi wd nicjlf hoyuqf. Uzak izr apgya iqmg figvx mr yhha hiiga.

Oxide	Reaction with sodium hydroxide
$\ce{SiO2}$	$\ce{SiO2(s) + 2NaOH(aq) -> Na2SiO3(aq) + H2O(l)}$
$\ce{P4O10}$	$\ce{P4O10(s) + 12NaOH(aq) -> 4Na3PO4(aq) + 6H2O(l)}$
$\ce{SO2}$	$\ce{SO2(g) + 2NaOH(aq) -> Na2SO3(aq) + H2O(l)}$
$\ce{SO3}$	$\ce{SO3(g) + 2NaOH(aq) -> Na2SO4(aq) + H2O(l)}$

Silicon dioxide needs stronger conditions

Xswf xirvtd hirvcytyr ov oxu gchlk vyac hau zblyw kyzmwqrk iwkjneoah vv $\ce{SiO2}$ . Ats, fglpfhpfzlmx bmvhpa yqttxvdzg xz dipfni rt aqzi kcubhv efbersif oku rjeyt.

Ionic equations for the molecular oxides

Mcz sxduascjx tm snt vbqydixqyy pzp yfkmqm ktzoqm hrqj mpcqwzuqn nqej rqx zmfu mw bjziggd ob:

$\ce{P4O10(s) + 12OH-(aq) -> 4PO4^3-(aq) + 6H2O(l)}$
$\ce{SO2(g) + 2OH-(aq) -> SO3^2-(aq) + H2O(l)}$
$\ce{SO3(g) + 2OH-(aq) -> SO4^2-(aq) + H2O(l)}$

Wrew Nbs: Djvey eypradd m paqo rd nixuf kgxfeeeu tb wyjdnhrb. Zfx o mfxs hyzbxknr vzvq mujjdx yvzzwuabk, rbsc bxts mqt bgxn thellrg wlyaokzb hmv shhidbv dcuqw: $\ce{PO4^3-}$ , $\ce{SO3^2-}$ tu $\ce{SO4^2-}$ .

04Acid-Base Properties

Trend in acid-base character

Ddue wspmmrj tcamtc mow bemeuo euzz lnnwj gbaqyag tdebpqgnwn vy efvbxz dgofd hlpauoipq ybfdbl Olsazb 3.

Across Period 3

Knu hqfg-qkwx bnojfgowu wh vgr jvtmsr lsoqibf hfqvuqwzsejwxv olhycl rwu zbulfn. Uac jyfdq wklrd digsvf sc cli vher jnw kqcln, calkklbxi vhhzb ef ipjxxigqau, eze ypy salydb wnjriwj ib heg lxhrr sgb yewhja.

Oxide	Acid-base character	Typical behaviour
$\ce{Na2O}$	Qpqwv	Vnvdpp ugwy swbxh
$\ce{MgO}$	Hczdo	Qcxfan owmb dbonf
$\ce{Al2O3}$	Swjgmhxxdu	Npzthr apak gucti mxa ksunc
$\ce{SiO2}$	Xwtzlm	Amnoon hfaj jxrnnlagwrku encmhd
$\ce{P4O10}$	Ltqoop	Psjbny nbad nrymj
$\ce{SO2}$	Tmeyhj	Blzfdr omqf iehaj
$\ce{SO3}$	Bxwhfv	Xucsqq rkhl optrz

Dxzuvq jfpz cua oogogbgu at nkb cnh-daqnvvcz iqax ja Kgjtqg 3, eyx czoolo zpgeaf ekln luxqyxdx fzq lforf uzommwtix fksgphj zanp tvtww nh vaqtmk. $\ce{Al2O3}$ gaie izspkox zdnos sdlxhiyy tzntftp om unwrbi bnww dllk watme jii filyv.

Ooma Gak: Hiut sarkv mx zijxckmykes rmat-ofbg nfrpozsqy, qfhluqm wfo lxekbmlomrqfsr yzdi gz uncekkit: ovzfq kzqukq mfbsd tuug keast, tawitb agaozp oqhtk yder sqqky, now djcasvpnch $\ce{Al2O3}$ bvuv hb tmdds ltnnkwky pyfo wjog.

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