22. Analytical techniques
A section of Chemistry, 9701
Listing 10 of 112 questions
A sample of but-2-enoic acid, CH3CH=CHCOOH, is analysed using infrared spectroscopy. The infrared spectrum shows a broad peak in the range 2500–3000 cm–1. bond functional groups containing the bond characteristic infrared absorption range (in wavenumbers) / cm–1 C–O hydroxy, ester 1040–1300 C=O amide carbonyl, carboxyl ester 1640–1690 1670–1740 1710–1750 C=C aromatic compound, alkene 1500–1680 C–H alkane 2850–2950 O–H carboxyl hydroxy 2500–3000 3200–3600 N–H amine, amide 3300–3500 C≡N nitrile 2200–2250 Which bond is responsible for this peak?
9701_s24_qp_13
MCQ
2024
Paper 1, Variant 3
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Compound W has molecular formula C4H10O. It contains only one functional group. Table 5.1 shows the two peaks with the greatest m / e values in the mass spectrum of W. Table 5.1 m / e relative abundance x Calculate the relative abundance, x, of the peak at m / e = 75 using the information from Table 5.1. x = The mass spectrum of W also shows peaks at m / e = 29 and m / e = 59. Suggest the molecular formulae of these fragments. m / e = 29 m / e = 59 A sample of W, C4H10O, is heated under reflux with an excess of acidified K2Cr2O7 until there is no further reaction. Only one organic product, X, is present in the mixture at the end of the reaction. shows the infrared spectrum of W. wavenumber / cm–1 transmittance / % A shows the infrared spectrum of X. wavenumber / cm–1 transmittance / % B Table 5.2 bond functional groups containing the bond characteristic infrared absorption range (in wavenumbers) / cm–1 C–O hydroxy, ester 1040–1300 C=C aromatic compound, alkene 1500–1680 C=O amide carbonyl, carboxyl ester 1640–1690 1670–1740 1710–1750 C≡N nitrile 2200–2250 C–H alkane 2850–2950 N–H amine, amide 3300–3500 O–H carboxyl hydroxy 2500–3000 3200–3650 Absorption A is shown in . Absorption B is shown in . Complete Table 5.3 using the information given in , and Table 5.2. Table 5.3 absorption bond functional group containing the bond A B , , Use the information in and to draw the structure of X in the box in . C4H10O W X acidified K2Cr2O7 + Y is a structural isomer of W. Both W and Y produce colourless bubbles when sodium is added to them. Y does not react when heated with acidified K2Cr2O7. Y does not react when warmed with alkaline I2. Name the functional group present in Y. Complete the equation to describe the reaction of W or Y with sodium. C4H10O + Na Draw the structure of Y. , ,
9701_s24_qp_22
THEORY
2024
Paper 2, Variant 2
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Explain with reference to energy states how 1H NMR can supply information about the structure of molecules. Nuclear magnetic resonance is used in magnetic resonance imaging scanners. These scanners are increasingly used in hospitals to detect tumours. Suggest why magnetic resonance techniques are better than X-rays. Examiner’s Use The NMR spectrum shown below was obtained from a simple organic molecule, G, CxHyO2. When a sample of G was placed in a mass spectrometer, the ratio of the M : M+1 peaks for the molecule was 14.5 : 0.66. absorbance chemical shift,  Calculate how many carbon atoms there are in the molecule. Use the NMR spectrum and the Data Booklet to work out the structure of G.
9701_w07_qp_4
THEORY
2007
Paper 4, Variant 0
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Use The technology of DNA fingerprinting has enormously advanced scientific identification techniques in medicine, crime detection and archaeology in recent years. In order to prepare a DNA sample for analysis, the DNA is treated with restriction enzymes. What do restriction enzymes do? What is the next stage in DNA analysis, after the treatment with restriction enzymes? How are the DNA fragments made visible? NMR and X-ray crystallography have made significant contributions to our knowledge of the structure of proteins and, in the pharmaceutical industry, how drugs react with target proteins. Suggest an advantage of each technique in helping to determine protein structure. MRI scanning is a medical technique based on NMR spectroscopy. It is particularly useful for looking for tumours in healthy tissue. Suggest how this technique can distinguish tumour tissue from healthy tissue. Examiner’s Use A saturated molecule of formula CxHyNO was subjected to analysis by mass spectrometry and NMR spectroscopy. In the mass spectrum of the compound, the M peak was at m/e 73 and the ratio of the heights of the M:M+1 peak was 48 : 1.7. Using the data from the mass spectrum, determine the values of x and y in the formula of the compound. Use the data from together with the NMR spectrum below to deduce a structure for the compound, explaining how you arrive at your answer. chemical shift,  / ppm
9701_w08_qp_4
THEORY
2008
Paper 4, Variant 0
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10 Instrumental methods of analysis have become increasingly important in recent years. The use of chromatography to separate substances, and NMR spectroscopy to identify them, has become routine in many laboratories. Chromatography relies on either partition or adsorption to help separate substances. Briefly explain how each method brings about separation. partition adsorption The table shows three different techniques of chromatography. Identify which separation method, partition or adsorption, applies to each. technique separation method paper chromatography thin-layer chromatography gas/liquid chromatography The diagram represents the output from gas/liquid chromatography carried out on a mixture. time injection detector response air peak solvent peak X Y Determine the percentage of each of the two components X and Y in the mixture. NMR spectroscopy is a very important analytical technique for use with organic compounds. Why is NMR spectroscopy particularly useful for organic compounds? Two molecules, propanal and propanone, have the same molecular formula, C3H6O. Draw the displayed formula of each compound and explain briefly how NMR spectroscopy can distinguish between the two structures.
9701_w10_qp_43
THEORY
2010
Paper 4, Variant 3
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A molecule of an organic compound, P, contains three carbon atoms and shows a strong absorption at 1720 cm–1 in its infrared spectrum. P is reacted with an excess of hot acidified potassium dichromate(forming organic product Q. Q shows a strong absorption at 1700 cm–1 and a strong, broad absorption centred at 2800 cm–1 in its infrared spectrum. bond functional group containing the bond characteristic infrared absorption range (in wavenumbers) / cm–1 C–O hydroxy, ester 1040–1300 C=C aromatic compound, alkene 1500–1680 C=O amide carbonyl, carboxyl ester 1640–1690 1670–1740 1710–1750 C≡N nitrile 2200–2250 C–H alkane 2850–2950 N–H amine, amide 3300–3500 O–H carboxyl hydroxy 2500–3000 3200–3600 What is P?
9701_w22_qp_12
MCQ
2022
Paper 1, Variant 2
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Questions Discovered
112