It seems that during your experiment with dissolving gold in aqua regia, you got an unexpected outcome. The colors turning black could mean that contaminants are present or that there was an unexpected reaction. Since sodium metabisulfite (SMB) is frequently used to precipitate gold from the solution, adding SMB was a wise move. If you're dubious of the result, though, getting help with university assignments from professionals in the industry for your academic paper on the subject might yield insightful information. Continue learning and trying; the secret to success is comprehending the chemistry underlying these reactions.
It seems that during your experiment with dissolving gold in aqua regia, you got an unexpected outcome. The colors turning black could mean that contaminants are present or that there was an unexpected reaction. Since sodium metabisulfite (SMB) is frequently used to precipitate gold from the solution, adding SMB was a wise move. If you're dubious of the result, though, getting help with university assignments from professionals in the industry for your academic paper on the subject might yield insightful information. Continue learning and trying; the secret to success is comprehending the chemistry underlying these reactions.