Chem 330 Week 4 notes
Chem 330 Week 4 notes Chem 330
Popular in Quantitative Analysis Chemistry
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This 4 page Class Notes was uploaded by Leslie Pike on Wednesday June 29, 2016. The Class Notes belongs to Chem 330 at Western Kentucky University taught by Dr. Darwin Dahl in Fall 2015. Since its upload, it has received 6 views. For similar materials see Quantitative Analysis Chemistry in Chemistry at Western Kentucky University.
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Date Created: 06/29/16
Reference electrodes Standard Hydrogen electrode (SHE) has reduction potential of 0.00V by definition. Pressure is 1 atm and [H+]=1.00. SHE is theoretical, cannot actually be achieved because [H+]=1 cannot be achieved due to activities. A real life SHE must be corrected with the Nernst equation. Example: you have a hydrogen electrode at 720 torr and a pH of 4. What is the potential? The reduction of hydrogen is: 2H+ + 2e- = H . 2 Using Nernst equation: 0 2 E = E – 0.0592/n*log(Q) = 0 – 0.0592/2*log((720/760)/(10^-4) ) = -0.236 V Remember to square the hydrogen concentration. Q expression is products over reactants raised to the balancing coefficients. Galvanic cell problems Calculating Kf for CuY given the following cell (Ka is 10^-7, Ecell = 0.5 V, Esilver = 0.799 V, Eanode = Ecathode – Ecell): Redox titration: Deviations Ecell = Ecathode – Eanode only holds true for ideal circumstances. It can deviate due to liquid junction potential (this deviation can be minimized by choosing an appropriate electrolyte), IR drop (caused by resistance within the battery itself, not present if current is not flowing) and polarization effects. Gas chromatography 2 Number of theoretical plates = 16 (Tr/w) . The more theoretical plates you have, the better peak separation you will have. The Van Deemter equation: H = A + B/μ + Cμ, where μ is the rate of flow of the carrier gas. A stands for eddy diffusion constant. It is caused by the fact that different molecules can take different length paths through the GC column (some might stay by the glass and some might weave through the packing material). It is independent of flow speed. B stands for longitudinal (or axial) diffusion. It is caused when the sample diffuses up or down the column because the carrier gas does not supply enough pressure to keep everything moving forward at the same rate. Decreases with flow rate. C stands for non-equivalency mass transfer. It increases as flow rate increases. A capillary tube does not have packing, and thus A=0. Resolution is therefore much higher.
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