IEB Grade 12 Acid-base reaction notes

Lowry -

Brolnsted model




}
>
anacidisa proton donor
important for the manufacture of
hydrochloric acid sulphuric acid nitric acid fertilizers Plastics and other useful
'

e' 9- - - .




>
products
abase is a proton acceptor

e. ammonium hydroxide
'


g.


Example / : Ñ+H>zOa ,
'

Chace, +
Hsotcaa,
Hclactsastheacidasitdonatesa proton / Ht )
-




Hzoactsasthebaseasit accepts the proton

A
II hydrogen atom contains only one proton and one electron When the hydrogen atom
:
.




loses an electron ,
a proton remains .
A proton is identified as a
hydrogen ion ( Ht )


'

Hzoa , Nlttcaq , OH caq )
-




Example
+
2 :
NHqg ,
+




Hzoactsastheacidasitdonatesa proton

NHsactsasthebaseas.it accepts the proton

examples water canactaseitheranacidorasa base
> both
in ,




>
amphiproticisa substance that can react asanacid with one substance ,
and can react

as abase with another substance ( H2O HCQIHSOÉ
,
)


Acid strength

> a
strong acid ionises
completely in an aqueous solution ionise completely ionise
Partially
> aweakacidionises partially in an aqueous solution T 14
strong acids weak acids strong weak


HCl acid HF acid
Hydrochloric Hydrofluoric HCl hydrochloric HF hydrofluoric
-
-




11-250<1 Sulphuric acid HZSO } Sulphurous acid HzSO¢ -



sulphuric Hasoz -


sulphurous

HNO , Nitric acid 1-131304 Phosphoric acid HNO , -

nitric HzPOa -



phosphoric

CHZCOOH Ethanol'C acid CHsCOOH -


ethanol'C

( COOH / z
Oxalic acid ( COOH )z -

oxalic

, Examples :
>
H NO , H2O NO3- +
Hzotcaq , hydronium
+
ion
caq ,
>
an acid ionises in water

>
ionisation is the reaction of a molecular substance with water to produce ions


proton donors
> in water , some acids are better


HCl + H2O Cliaqit Hs 07am
>
hydrochloric acid is a
good proton donor and so the solution consists largely of ions
>
equilibrium ties to the right ,
which means that this acid is nearly 100% ionized (conductive )
HCl is acid in water
> a
strong


The equilibrium constant ( Ka ) for acids HCl H2O Cliaq , +
Hsotcaq ,
strong
: +




value of Ka
very high ( > 10001
>
is

>
because the acid is almost 100% ionised

this means that the concentration of hydronium ions and chloride ions is
very high compared
>



to the concentration of the un -
ionised molecules ( HCI )


The equilibrium constant ( Ka ) for weak acids :
H Figs
+
Hzoa , Fiaq , +
Hs 0 Yaa ,
>
value of Ka is
very low equilibrium ties to the left
>
because the acid ionises only partially in water

> this means that the concentration of hydronium ions and fluoride ions is low compared to

the concentration of the un -
ionised molecules ( HF )




Equations for the ionisation of other acids

Hzsoacaql +
211-20111 2 Hzotcaq , +
5042 Iaql
CH } COOH caql H 20111 ¥ Hzotcaq ,
-




+ +
CH , COO ( aat

Hs POA ( aq )
+
3h20 (1) ¥3 Hzotcaq , +
POE( aq )