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What is the final chemical form of Gold (Au) when it is dissolved in aqua-regia?
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The correct answer is:
$\left[\mathrm{AuCl}_4\right]^{-}$
When gold (Au) dissolved in aqua-regia, it forms chloroauric $\left(\mathrm{HAuCl}_4\right)$ ion. It will react very slowly with chlorin gas at room temperature to form gold chloride. We know that aqua-regia is
$$
\mathrm{Au}+\mathrm{HCl}+\mathrm{HNO}_3 \stackrel{3 \mathrm{Cl}+\mathrm{HNO}_3}{\left.\mathrm{HuCl}_4\right]^{-}}
$$
$$
\mathrm{Au}+\mathrm{HCl}+\mathrm{HNO}_3 \stackrel{3 \mathrm{Cl}+\mathrm{HNO}_3}{\left.\mathrm{HuCl}_4\right]^{-}}
$$
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