Lab Tips in Kinetics
1H NMR
1H NMR, or proton nuclear magnetic resonance spectroscopy, is a technique for the identification and quantification of organic compounds. Basically, an NMR spectrum looks like this. Each peak corresponds to a proton or group of protons in a compound. The size of the peak corresponds to the concentration of those protons.
Once a reaction starts, peaks for the reactants will disappear and peaks for the products will grow. From this, the rate of the reaction can be found.
When you are done, you can put all of the pictures together to get a time lapse view of the reaction, sort of like a chemistry flip book. Some peaks will look like eroding mountains, others like new volcanoes.
IR
IR, or infrared spectroscopy, shoots infrared beams at samples.—Dr. Evil approves, as long as sharks are involved, or at least ill-tempered sea bass. Different samples will absorb different wavelengths of the laser, depending on the compounds that are present in the sample. If a reaction occurs, new compounds are created. As a result, different wavelengths will be absorbed.
Much like the NMR example, we can determine concentration by measuring the size of a peak in a sample. Since we know the reaction time when each measurement is taken, we can then solve for the reaction rate.
UV-VIS
UV-Visible spectroscopy is similar to IR spectroscopy. They're sort of twinsies. The biggest difference is that IR spectroscopy uses infrared beams while UV-VIS spectroscopy uses a light source that generates visible and UV light. Everything else is the same.
GC
Gas chromatography, or GC, is a technique that separates a mixture into its components. The components can then be quantified using a variety of detectors. Call them sniffers if you want to get a chemist to laugh. As with the other instruments, the size of the detected peak can be measured and the concentration calculated.
