溶液PH值计算0.1 mol/l NaH2PO4H3PO4 pKa1=2.12 pKa2=7.2 pKa3=12.36

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溶液PH值计算0.1 mol/l NaH2PO4H3PO4 pKa1=2.12 pKa2=7.2 pKa3=12.36
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溶液PH值计算0.1 mol/l NaH2PO4H3PO4 pKa1=2.12 pKa2=7.2 pKa3=12.36
溶液PH值计算
0.1 mol/l NaH2PO4
H3PO4 pKa1=2.12 pKa2=7.2 pKa3=12.36

溶液PH值计算0.1 mol/l NaH2PO4H3PO4 pKa1=2.12 pKa2=7.2 pKa3=12.36
质子条件式:
[H+]+[H3PO4]=[HPO4-2]+2[PO4-3]+[OH]
则:
[H+]+[H+][H2PO4-1]/Ka1+Kw/[H+]
=[HPO4-2]+2Ka3[HPO4-2]/[H+]+Kw/[H+]
=[HPO4-2](1+2Ka3/[H+])+Kw/[H+]
因为2Ka3/[H+]《1,
所以[H+]+[H+][H2PO4-1]/Ka1
=[HPO4-2]+Kw/[H+]
又因为Kw《Ka2[H2PO4-1]
所以[H+]+[H+][H2PO4-1]/Ka1
=Ka2[H2PO4-1]/[H+]
则[H+]=(Ka2[H2PO4-1]/(1+[H2PO4-1]/Ka1))0.5=2.11e-5
故pH=4.68其中c(H2PO4-1)≈[H2PO4-1]