# Concentration for a group of standard solutions and

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• drasman
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plots the different Absorbances vs. Concentration for a group of standard solutions and then our unknown. Because our unknown falls within the range of standard Absorbances we are then able to simply calculate it using the equation of our line in standard formula (y = mx + b). This works because our standard solutions generate data that makes a linear line that our unknown value falls into. The unknown (our penny) had an absorbance of 0.310, which is going to be a “y” value for this lab. By plugging in y you now have 0.310 = mx + b, and m and be are constants already generated by labquest based on our trendline. Solving for this gives you x = 0.207, or its concentration based upon the observed Absorbance. Since the percentage of copper seemed off I redid the standard curve in Excel. I plotted all the same points and excluded the 0.060g concentration. This time I calculated x to be 0.089536 which produced a concentration value of 3.53%. This could be due to us making a mistake while graphing and or printing the data from our Lab Quest. Excel is much friendlier c.Complexing for color is another important method in this lab. As things become more concentrated we expect them to get darker and absorb more light (i.e. have a
higher absorbance reading). This held true for our standard curve data. The more concentrated the standard solution, the higher its absorbance reading. Progressively moving to lower and lower concentrations produced lighter colored solutions as well as lower absorbance values. Once dissolved with water and ammonium hydroxide added, our penny was very similar to the color of our 0.100 g/250 mL solution, which makes sense because its absorbance reading was close as well. F.Reflection:a.Based on class data as the age of the penny increases so does its percentage of copper. Therefore, the newer pennies contain less copper (because we are cheap) and the older pennies contain more copper. After a bit of research, I found that our overall class data was good because pennies are now made up of a mixture of other metals including zinc, with a copper outer coating. The majority of the penny is no longer made of copper and therefore the newer pennies contain less copper. Other than a few blips in the data (1981 and 2000), the graph of copper concentration vs penny year would be fairly linear with a negative slope.b.Ammonium hydroxide was added to our copper standard solutions at
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