计算用NaOH(0.10mol/L)滴定HCOOH(0.10mol/L)到化学计量点时溶液的pH,并说明应选择何种指示剂? 计算0.10mol/l甲酸溶液的ph和离解度
NaOH\u6ef4\u5b9aHCOOH\u7532\u9178\u5206\u6790\u6709\u56fd\u5bb6\u6807\u51c6\u7684\uff0c\u7528\u915a\u915e\u6307\u793a\u5242\u3002
\u5316\u5b66\u8ba1\u91cf\u70b9\u65f6\u6eb6\u6db2\u4e3aHCOONa \u6d53\u5ea6\u4e3a0.050mol/l HCOO- + H2O HCOOH+ OH- Kh=Kw/Ka(HCOOH)=KW/1.77\u00d710^-4=5.64\u00d710^(-11) \u7531\u4e8eKh•C>20Kw \u4e14C/Kh=0.050/ [5.64\u00d710^(-11) ]>500 \u56e0\u6b64\u53ef\u7528\u6700\u7b80\u516c\u5f0f: [OH-]=(Kh•C)^(1/2)=[0.050\u00d7 5.64\u00d710
这个需要查到HCOOH的Ka=1.8*10^-4HCOO-+H2O====HCOOH +OH- Kb=Kw/Ka=5.56*10^-11
中和滴定后, c(HCOO-)=0.05mol/L ,c/Kb>500.可以用最简公式
c(OH-)=根号下(cKb)=根号下 0.05*5.56*10^-11
=1.67*10-6
pH=14-pOH =14+lg(1.67*10-6 )=8.2
NaOH + HCOOH --> HCOONa + H2O 生成物HCOONa水解呈碱性,所以用酚酞就可以了。
PH大于7 因为生成物会水解 用酚酞
用酚酞,查出HCOONa的水解率才能算
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