Doreen Foy Organic chemistry laboratory 1 Hannah ...
Doreen Foy Organic chemistry laboratory 1 Hannah Loch 10/15/12 Gas Chromatography Worksheet Questions Part 1: General questions 1. Gas chromatography is a separation technique for separating organic compounds that can be vaporized without decomposition. Separation is based on boiling point, volatility and polarity. It is also used to check sample purity and purify substances on a really small scale. 2. As a gaseous mixture travels through a gas chromatography column, it travels in a carrier gas, usually an inert gas. The gaseous mixture equilibrates between the gas (mobile) and liquid (stationary) phases. Partitioning between the two phases is based upon differences in physical properties of the components. The length of time required for a sample to move through a column depends on how much time each component of the mixture spends in the vapor and liquid phases, which in turn depends on their partition coefficient. The greater the partition coefficient of the component, the more time it spends in the stationary phase and the longer it stays in the column. The smaller the partition coefficient of the gas mixture’s components, the longer they stay in the mobile phase, and the faster they travel through the column. Also, components with a low boiling point, hence high vapor pressure, travel through the column faster than components with high boiling points/low vapor pressure. 3. I predict that t-butanol will elude first, followed by 1-butanol and then 1-pentanol. From their structures, I can predict that t-butanol has the lowest boiling point than the two other molecules since it is more symmetric and has less surface area, so it has less intermolecular interactions ( for example Van Der Waals forces and London forces). 1butanol eludes next because it has a shorter chain than 1-pentanol, hence will have less intermolecular interactions and will have a lower boiling point. 1-Pentanol eludes last because it has the highest boiling point since it has more intermolecular interactions. All three compounds have some degree of hydrogen bonding but I predict that the degree of hydrogen bonding is similar in all three compounds since they all contain only one hydrogen atom and so it is negligent in comparing the boiling points of the compounds.
4. The Kp for 1-butanol is expected to be smaller than the Kp for 1-penatanol in a gas chromatography experiment.
Doreen Foy Organic chemistry laboratory 1 Hannah Loch 10/15/12 5. Draw block diagram for Gas chromatography
6. The fact that helium is an inert gas means it is non-reactive with the analytes and thus makes it a good carrier. It also has a low boiling point (high vapor pressure) and a high thermal conductivity. Helium is also available in a relatively pure state.
7. The injection port should be heated to a temperature of about 250°C-300°C to ensure that all sample components vaporize. (UNSURE) 8. In gas chromatography, a good solid support is one that is non-reactive with the analyte earth. A good stationary phase is one coated with a viscous liquid that has a high boiling point and is a non-volatile. 9. Constant oven temperature ensures efficient separation of the components because you need the analytes to elude to at specific times because if the temperature is fluctuating, then separation is useless.. 10. The detector column used in the gas chromatograph instrument was the Thermal Conductivity Detector and it is non-destructive. 11. A flame ionization detector is desirable when detecting carbon containing compounds that are sensitive to flame. 12. When a signal is too large for the chromatograph recorder, you should increase the attenuation. 13. In a gas chromatography experiment, a good resolution is a characteristic of two adjacent peaks. It means how well two adjacent peaks can be said to differ from each other. Therefore a good resolution is when two adjacent peaks do not overlap. 14. You can adjust the settings on a GC to correct for overlapped peaks by changing the flow rate. 15. Three other types of chromatography are Column Chromatography, Thin Layer Chromatography (TLC) and High Performance Liquid Chromatography (HPLC). Column Chromatography and GC are similar in that they are both used to separate
Doreen Foy Organic chemistry laboratory 1 Hannah Loch 10/15/12 organic compounds; they both have a mobile phase and a stationary phase and can both be used to test the purity of mixtures. They are different in that the mobile phase in GC is an inert gas and the stationary phase is a non-volatile liquid whereas in Column Chromatography, the mobile phase is either a polar or non-polar liquid (it depends on the nature of the components to be separated). The stationary phase in Column Chromatography is usually a polar solid (either silica gel or alumina). (include citation) Part 2: Experiment
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Doreen Foy Organic chemistry laboratory 1 Hannah Loch 10/15/12
4. The Kp for 1-butanol is expected to be smaller than the Kp for 1-penatanol in a gas chromatography experiment.
Doreen Foy Organic chemistry laboratory 1 Hannah Loch 10/15/12 5. Draw block diagram for Gas chromatography
6. The fact that helium is an inert gas means it is non-reactive with the analytes and thus makes it a good carrier. It also has a low boiling point (high vapor pressure) and a high thermal conductivity. Helium is also available in a relatively pure state.
7. The injection port should be heated to a temperature of about 250°C-300°C to ensure that all sample components vaporize. (UNSURE) 8. In gas chromatography, a good solid support is one that is non-reactive with the analyte earth. A good stationary phase is one coated with a viscous liquid that has a high boiling point and is a non-volatile. 9. Constant oven temperature ensures efficient separation of the components because you need the analytes to elude to at specific times because if the temperature is fluctuating, then separation is useless.. 10. The detector column used in the gas chromatograph instrument was the Thermal Conductivity Detector and it is non-destructive. 11. A flame ionization detector is desirable when detecting carbon containing compounds that are sensitive to flame. 12. When a signal is too large for the chromatograph recorder, you should increase the attenuation. 13. In a gas chromatography experiment, a good resolution is a characteristic of two adjacent peaks. It means how well two adjacent peaks can be said to differ from each other. Therefore a good resolution is when two adjacent peaks do not overlap. 14. You can adjust the settings on a GC to correct for overlapped peaks by changing the flow rate. 15. Three other types of chromatography are Column Chromatography, Thin Layer Chromatography (TLC) and High Performance Liquid Chromatography (HPLC). Column Chromatography and GC are similar in that they are both used to separate
Doreen Foy Organic chemistry laboratory 1 Hannah Loch 10/15/12 organic compounds; they both have a mobile phase and a stationary phase and can both be used to test the purity of mixtures. They are different in that the mobile phase in GC is an inert gas and the stationary phase is a non-volatile liquid whereas in Column Chromatography, the mobile phase is either a polar or non-polar liquid (it depends on the nature of the components to be separated). The stationary phase in Column Chromatography is usually a polar solid (either silica gel or alumina). (include citation) Part 2: Experiment
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Doreen Foy Organic chemistry laboratory 1 Hannah Loch 10/15/12
