[CHEM]pKa

octopus001

20cm^3 of 0.1M weak acid, HX ,
given pH=4.55 , 用左20cm^3的0.1M NaOH 去neutralize....

問pKa=?

我想問點計....
點解 個no. of mole of X- =no. of mole of NaOH ????

Zend

trival question
書有的, 自己再花時間想想

for weak acid

x  0 0
x-a a a
Ka= a^2/(x-a) ~= a^2/x
a=sqrtKax=[H+]
-log[H+]=pH=-logsqrt Ka.x
where x is the concentration of acid

if Ka is not too small ge, solve quartic equation la.... i.e. Ka>10^-4

octopus001

點解 個no. of mole of X- =no. of mole of NaOH ????

Zend

neutralization

octopus001

我係咁titrate NaOH, 咁個acid 咪係咁 dissociate...
conc. of acid 咪唔係in eqm lo =.=?
個no. of mole of X- =no. of mole of NaOH 咪好似冇意思

Zend

所以有樣野叫buffer range.

octopus001

=.=""" buffer 未識住 -.-"""
咁我條問題...... 冇得解 =.=?

Zend

你連pH=pKa+log[salt]/[acid]都未學?

我只能講, 這是approximation

你要明, 讀到果PART 自然會明

octopus001

pH=pKa+log[salt]/[acid] 我知ar...
buffer 係咪 weak acid 係水到ar?

Zend

你知個公式點推出來就知咩事