Sound Writing

Example 5.18.20. Results: Biology.

The lowest light intensity (0 $\mu {\text{mol photons m}}^{-2}{\text{s}}^{-1}$) showed the lowest and only negative average change in dissolved oxygen ($\mathrm{\Delta }\text{DO}$), at $-0.162\pm 0.058$ mg/L-hr (Figure 1). At light intensities of 10 and 30 $\mu {\text{mol photons m}}^{-2}{\text{s}}^{-1}$ the $\mathrm{\Delta }\text{DO}$ increased from $0.267\pm 0.038$ to $0.562\pm 0.062$ mg/L, hr for a 53% increase in average $\mathrm{\Delta }\text{DO}\text{.}$ From light intensities 30 to 50 $\mu {\text{mol photons m}}^{-2}{\text{s}}^{-1}$ the average $\mathrm{\Delta }\text{DO}$ increased 11% (to $0.562\pm 0.062$ to $0.762\pm 0.021$ mg/L, hr). The standard errors of average $\mathrm{\Delta }\text{DO}$ for light intensities 0 to 50 fell between .04 to .06 without any overlap, and thus were all statistically different from one another. There was a notable increase (over 200%) in ${\text{O}}_2$ production from light intensity 0 to 80 $\mu {\text{mol photons m}}^{-2}{\text{s}}^{-1}\text{,}$ and a generally positive relationship between light intensity and $\mathrm{\Delta }\text{DO}$ from 0 to 80 $\mu {\text{mol photons m}}^{-2}{\text{s}}^{-1}\text{.}$ $\mathrm{\Delta }\text{DO}$ plateaued after 80 $\mu {\text{mol photons m}}^{-2}{\text{s}}^{-1}\text{.}$ The $\mathrm{\Delta }\text{DO}$ at light intensities 80, 140, 200, and 380 $\mu {\text{mol photons m}}^{-2}{\text{s}}^{-1}$ were not statistically different from each other, and ranged from 0.7 to 1.1 mg/L, hr (including overlapping standard error).

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Figure 1 Increasing light intensity causes an increase in Elodea canadensis photosynthetic activity up to 80 $\mu {\text{mol photons m}}^{-2}{\text{s}}^{-1}\text{.}$

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Samples of dark-adapted Elodea canadensis in diluted sodium bicarbonate solution were introduced to a bank of lights at varying light intensities for 90 minutes, and change in the dissolved oxygen value (mg-$L^{-1}$) of the sodium bicarbonate solution was measured as a marker of photosynthetic activity. From light intensities of 10 to 30 $\mu {\text{mol photons m}}^{-2}{\text{s}}^{-1}$ the average $\mathrm{\Delta }\text{DO}$ increased by 53%. From light intensities 30 to 50 $\mu {\text{mol photons m}}^{-2}{\text{s}}^{-1}$ the average $\mathrm{\Delta }\text{DO}$ increased by 11%. There was a notable increase (over 200%) in ${\text{O}}_2$ production from light intensity 0 to 80 $\mu {\text{mol photons m}}^{-2}{\text{s}}^{-1}\text{.}$ $\mathrm{\Delta }\text{DO}$ plateaued after 80 $\mu {\text{mol photons m}}^{-2}{\text{s}}^{-1}\text{.}$ Elodea canadensis shows the most efficient use of light energy for ${\text{O}}_2$ production at 80 $\mu {\text{mol photons m}}^{-2}{\text{s}}^{-1}\text{.}$

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Example 5.18.21. Results: Chemistry.

The mass of the Erlenmeyer flask, stopper, and air within it was measured to be 143.6151g, and the calculated mass of the air within the flask was 0.31034g. Subsequently the mass of the empty flask (flask with air and stopper mass minus the air mass) was found to be 143.3053g. The volume of water that filled the flask was measured to 265 mL, so the volume of the flask was said to be 265 mL, or 0.265 L.

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Table 1 gives reagent information about all the gases that could have been encountered in the experiment. Each gas was a possibility for the identity of the unknown gases.

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Table 2 summarizes the data measured and calculated about each unknown gas, as well as the results of their reaction with a flame.

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The mass of the sample of Unknown Gas 1 was 0.4282g. Using this, the molar mass of the gas sample was found to be 39.97601 g/mole. The mass of the Unknown Gas 2 sample was 0.3852g, and the molar mass of the gas sample was then found to be 35.9581 g/mole. The Unknown Gas 3 mass was 0.4561g, and the molar mass of the gas sample was calculated to be 42.5765 g/mole (see appendix for calculations).

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The hypotheses for each unknown gas’s identity were supported by the flame test results, except for Unknown Gas 1. The gas was confirmed to be inert by the flame test, yet to narrow the gas’s identity possibilities down to one, further testing was needed. Unknown Gas 1 was subjected to the limewater test. The ${\text{Ca(OH)}}_{2(aq)}\text{,}$ when added to the gas in the flask, formed a whitish grainy precipitate in the liquid.

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