求分析化学大师指导这道题PH为什么等于8.难道pkb=pH?

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求分析化学大师指导这道题PH为什么等于8.难道pkb=pH?
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求分析化学大师指导这道题PH为什么等于8.难道pkb=pH?
求分析化学大师指导这道题PH为什么等于8.难道pkb=pH?
 

求分析化学大师指导这道题PH为什么等于8.难道pkb=pH?
估计是试题的假设
A- +H2O HA + OH-
Kb=Kw/Ka=10^-8.900
pH=8.9000 pOH=5.1000 [OH-]= 10^-5.1000
A- + H2O HA + OH-
起始:c 0 0
平衡:c-10^-5.100 10^-5.100 10^-5.100
Kb=(10^-5.100)* (10^-5.100 )/(c-10^-5.100)
10^-8.900=约=(10^-5.100)* (10^-5.100 )/c
c=10^-1.300 =0.05mol/L
===
如果pH=9.00
pOH=5.00 [OH-]= 10^-5.00
A- + H2O HA + OH-
起始:c 0 0
平衡:c-10^-5.00 10^-5.00 10^-5.00
Kb=(10^-5.00)* (10^-5.00 )/(c-10^-5.00)
10^-9.00=约=(10^-5.00)* (10^-5.00 )/c
c=10^-1.00 =0.1mol/L
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