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AQA A2 Analytical
| Question | Answer |
|---|---|
| In NMR why must a deuterated solvent be used? Your answer should include an example. | D2O has an even nucleon number therefore, no spinning occurs and the solvent will not interfere with the peaks produced by the compound tested. In other words the compound must dissolve in something which will not produce its own spectrum. |
| How many carbon environments are in butanol? | 4 |
| In a proton NMR spectrum, if a peak is split into a doublet how many hydrogen atoms are on adjacent carbon? | 1 |
| State what the relative area under each peak shows? | The relative number of H atoms in each environment |
| Describe the requirements for NMR spectroscopy | a strong magnetic field applied using an electromagnet and low-energy radio-frequency radiation. |
| State what is meant by the term chemical shift. | symbol = δ (delta) a scale that compares frequency of an NMR absorption with the frequency of the reference peak of TMS at δ=0ppm |
| State the two types of NMR Spectroscopy. | Carbon-13 and proton NMR. |
| Give two industrial uses of NMR Spectroscopy. | In pharmaceuticals (drugs and medicines) and in MRI scanning. |
| State three types of analytical techniques that you could use. | NMR, Mass spec and Infrared. |
| State what is meant by a quartet on a H-1 NMR | The adjacent carbon has three hydrogen atoms, such as C-CH3 |
| Describe how you would determine the number of different carbon environments from a carbon-13 NMR spectra | Count the number of peaks on the spectra. |
| Explain the splitting patterns in a 1H NMR graph. | If there a peak that is 3cm high and is around 1, with it being split into 3 peaks, this means that this is a CH3 and in the neighbouring carbon there are 2 hydrogens. |
| Why is TMS used for NMR? | TMS is the solvent used for NMR and it is used because there are no protons so there will be no extra peaks on the graph |
| What bonds are removed when D20 is added to a mixture (NMR)? | D20 will remove bonds such as N-H and O-H because D20 has no magnetic properties |
| What does a doublet with intensity 2 on an NMR indicate? | That there are 2 hydrogens (CH2) and one hydrogen on the adjacent carbon atom. |
| What is a disadvantage of Gas Chromatography? | It only works with volatile samples |
| State two advantages of Gas Chromatography. | The compound is separated and analysed very quickly and Only a small amount of the compound is needed for analysis |
| Explain what is meant by retention time? | The time it takes for a solute to travel through the column (oven) |
| What is the problem with calculating retention time for different compounds? | They may have similar retention times so identification is not possible |
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UrsulineChem
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