关于Na2S中离子浓度的比较
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关于Na2S中离子浓度的比较
如何判断浓度HS->H+?
如何判断浓度HS->H+?
不妨先设 1 摩尔Na2S溶于一升水中.
S2- + H2O HS- + OH-
(1) Ka1 = 9.6x10^-8 = [HS-][OH-]/[S2-]
HS- + H2O H2S + OH-
(2) Ka2 = 1.3x10^-14 = [H2S][OH-]/[HS-]
H2O H+ + OH-
(3) Kw = [H+][OH-] = 10^-14
又,
(4)[S2-] + [HS-] + [H2S] = 1 (M)
(5)[OH-] = [H+] + [HS-] + 2[H2S]
(6)2[S2-] + [HS-] + [OH-] - [H+] = 2 (M)
判断:5个未知量,六个方程式.应该有解.
从这六个方程,逐步消去其他项.最后只留关系式含 [HS-],{H+]和一些常数项------得结论.
S2- + H2O HS- + OH-
(1) Ka1 = 9.6x10^-8 = [HS-][OH-]/[S2-]
HS- + H2O H2S + OH-
(2) Ka2 = 1.3x10^-14 = [H2S][OH-]/[HS-]
H2O H+ + OH-
(3) Kw = [H+][OH-] = 10^-14
又,
(4)[S2-] + [HS-] + [H2S] = 1 (M)
(5)[OH-] = [H+] + [HS-] + 2[H2S]
(6)2[S2-] + [HS-] + [OH-] - [H+] = 2 (M)
判断:5个未知量,六个方程式.应该有解.
从这六个方程,逐步消去其他项.最后只留关系式含 [HS-],{H+]和一些常数项------得结论.