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HW 8-calibration curves key

HW 8-calibration curves key - HW 8 Key 1 Use the following...

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HW 8 Key 1. Use the following mass spectrometry data and blank to construct a calibration curve with trend line: CH 4 (vol%): 0 0.062 0.122 0.245 0.486 0.971 1.921 Signal (mV): 9.1 47.5 95.6 193.8 387.5 812.5 1671.9 Blank correcting the signal means subtracting the blank signal (9.1 mV) from all other signals. The blank-corrected table is: CH 4 (vol%): 0 0.062 0.122 0.245 0.486 0.971 1.921 Signal (mV): 0 38.4 86.5 184.7 378.4 803.4 1662.8 Plotting vol% vs corrected signal gives the following plot: (Make sure axes are labeled with a name and appropriate units). Replicate measurements of an unknown gave 152.1, 154.9, 153.9, and 155.1 mV, and a blank gave 8.2, 9.4, 10.6, and 7.8 mV. (a) Find the concentration of the unknown. Average unknown: 152.1+154.9+153.9+155.14 = 154.0 Average blank: 8.2+9.4+10.6+7.84 = 9.0 Blank-corrected unknown value: 154.0-9.0 = 145.0 % by vol of unknown methane concentration: 145.0 = 869.13 x – 22.085 x = 0.192% methane by vol. y = 869.13x ‐ 22.085 R² = 0.99925 ‐200 0 200 400 600 800 1000 1200 1400 1600 1800 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Signal(mV) Amount of methane (% by vol) Signal versus % Methane
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(b) Why might the replicate series of blanks be taken right before the unknown rather than for the calibration curve? What might be good or bad about doing that?
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