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Please help me with this concentration question! Watch

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    So I've been carrying out an experiment using spectroscopy. I dissolved a penny weighing 3.599g in 20cm3 of nitric acid. Then I poured this solution into a 100cm3 volumetric flask and made up to the mark with water. Then I divided these in 4 beakers of 25cm3 and added 2cm3 of ammonia to each. After this, I extracted 4 mls of this solution and poured it into a test tube, and added 4ml of deionised water. After shaking it, I pipetted the solution into a 1cm3 cuvette (3/4 of the way) and measured the absorbance. Using beers law I calculated the concentration to be = 0.000396695 however I am assuming because of the dilutions this is not the concentration of the original brass solution therefore it won't get me the correct mass. How do I go about this? Please help
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