Ushaped_solubility_diagram.ipynb

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    "# U shaped solubility diagram\n",
    "\n",
    "For Fe$^{3+}$ we can have Fe(OH)$_{3(\\mathrm{s})}$ form as a solid phase\n",
    "\n",
    "$\\mathrm{Fe(OH)}_{3(\\mathrm{s})} \\leftrightharpoons \\mathrm{Fe}^{3+} + 3\\mathrm{OH}^-$\n",
    "\n",
    "with $K_{sp}$=10$^{-38.8}$\n",
    "\n",
    "There are also 3 overall deprotonation reactions with $\\beta_{a1}=10^{-2.19}$, $\\beta_{a2}=10^{-5.7}$ and $\\beta_{a4}=10^{-21.6}$.  Note: some databases include a $\\beta_{a3}$ but the formation of Fe(OH)$_3$ as an aqueous species is not confirmed.\n"
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   "source": [
    "%plot -s 600,500 -f 'svg'\n",
    "pH=2:0.1:12;\n",
    "Ksp=10^-38.8;\n",
    "B1=10^-2.19;\n",
    "B2=10^-5.7;\n",
    "B4=10^-21.6;\n",
    "Kw=1e-14;\n",
    "logFe=log10(Ksp./Kw^3)-3*pH; Fe=10.^logFe;\n",
    "logFeOH=log10(B1*Ksp/Kw^3)-2*pH; FeOH=10.^logFeOH;\n",
    "logFeOH2=log10(B2*Ksp/Kw^3)-pH; FeOH2=10.^logFeOH2;\n",
    "logFeOH4=log10(B4*Ksp./Kw^3)+pH; FeOH4=10.^logFeOH4;\n",
    "FeT=Fe+FeOH+FeOH2+FeOH4; logFeT=log10(FeT);\n",
    "figure(1)\n",
    "plot(pH,logFe,'linewidth',2,pH,logFeOH,'linewidth',2,pH,logFeOH2,'linewidth',2,...\n",
    "pH,logFeOH4,'linewidth',2,pH,logFeT,'linewidth',2)\n",
    "set(gca,'linewidth',2,'fontsize',12);\n",
    "xlabel('pH','fontsize',12)\n",
    "ylabel('log[species]','fontsize',12)\n",
    "legend('Fe^{3+}','FeOH^{2+}','Fe(OH)_2^+','Fe(OH)_4^-','Fe_T','location','southwest');\n",
    "figure(1)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "ans = -58.599\n"
     ]
    },
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       "<IPython.core.display.SVG object>"
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   ],
   "source": [
    "% plot over a more narrow range\n",
    "plot(pH,logFe,'linewidth',2,pH,logFeOH,'linewidth',2,pH,logFeOH2,'linewidth',2,...\n",
    "pH,logFeOH4,'linewidth',2,pH,logFeT,'linewidth',2)\n",
    "set(gca,'linewidth',2,'fontsize',12)\n",
    "xlabel('pH','fontsize',12)\n",
    "ylabel('log[species]','fontsize',12)\n",
    "legend('Fe^{3+}','FeOH^{2+}','Fe(OH)_2^+','Fe(OH)_4^-','Fe_T','location','north')\n",
    "axis([2 10 -11 -3])"
   ]
  }
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