22. Analytical techniques
A section of Chemistry, 9701
Listing 10 of 112 questions
DNA fi ngerprinting has become an important analytical technique, largely due to its use in ‘screening’ crime suspects. It also has a range of applications in modern analysis including determining family links, medicine and archaeology. DNA fi ngerprinting uses an analytical technique you have studied. What is the name of that technique? In order to carry out DNA fi ngerprinting, the DNA must fi rst be broken down into shorter lengths of polynucleotides. How is this accomplished? What part of the DNA fragments enables them to move in an electric fi eld? The DNA fi ngerprints shown were obtained from a crime scene. DNA samples were recovered from two rooms in the house where the crime took place. The victim’s DNA and that of two possible suspects were included in the analysis. victim suspect 1 suspect 2 crime scene 1 crime scene 2 start point Indicate with an X on the diagram, which lines from suspect 1 and from suspect 2 cannot distinguish which of them was present in the house. Based on this evidence one suspect was arrested. Which suspect would you expect this to be? Explain your reasoning. A sample of a liquid, P, was found at the scene of the crime and was analysed using mass spectrometry and NMR spectroscopy. The mass spectrum has M and M+1 peaks in the ratio of 5.1: 0.22 with the M peak at m/e = 88. The NMR spectrum is shown δ / ppm Use the data to suggest a structure for P, explaining your answer. structure of P
9701_w12_qp_42
THEORY
2012
Paper 4, Variant 2
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Electrophoresis is a technique which can be used to separate amino acids or peptide fragments present in a mixture. Draw a diagram to show the apparatus used to carry out electrophoresis. You should label each of the relevant parts of the apparatus. How far an amino acid will travel during electrophoresis depends on the pH of the solution. For a given potential difference, state two other factors that will affect how far a given amino acid travels in a fi xed time during electrophoresis. 1. 2. A number of analytical and separation techniques rely on substances having different partition coeffi cients. State what is meant by the term partition coeffi cient. The partition coeffi cient of X between ethoxyethane and water is 40.0. A solution contains 4.00 g of X dissolved in 0.500 dm3 of water. Calculate the mass of X that can be extracted from this aqueous solution by shaking it with 0.050 dm3 of ethoxyethane, two successive portions of 0.025 dm3 of ethoxyethane.
9701_w13_qp_41
THEORY
2013
Paper 4, Variant 1
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Electrophoresis is a technique which can be used to separate amino acids or peptide fragments present in a mixture. Draw a diagram to show the apparatus used to carry out electrophoresis. You should label each of the relevant parts of the apparatus. How far an amino acid will travel during electrophoresis depends on the pH of the solution. For a given potential difference, state two other factors that will affect how far a given amino acid travels in a fi xed time during electrophoresis. 1. 2. A number of analytical and separation techniques rely on substances having different partition coeffi cients. State what is meant by the term partition coeffi cient. The partition coeffi cient of X between ethoxyethane and water is 40.0. A solution contains 4.00 g of X dissolved in 0.500 dm3 of water. Calculate the mass of X that can be extracted from this aqueous solution by shaking it with 0.050 dm3 of ethoxyethane, two successive portions of 0.025 dm3 of ethoxyethane.
9701_w13_qp_42
THEORY
2013
Paper 4, Variant 2
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Explain what is meant by the term partition coeffi cient. When 20 cm3 of ethoxyethane were shaken with 75 cm3 of an aqueous solution containing 5.00 g of an organic compound, J, in 75 cm3 of water, it was found that 2.14 g of J were extracted into the ethoxyethane. Calculate the partition coeffi cient, Kpartition, of J between ethoxyethane and water. Kpartition = In a new experiment ● 10 cm3 of ethoxyethane were shaken with 75 cm3 of an aqueous solution containing 5.00 g of J and the layers were separated. ● The aqueous layer was shaken with a second 10 cm3 portion of ethoxyethane and the layers were separated. ● The two organic layers were combined. Use the value of Kpartition you calculated in to calculate the total mass of J extracted by this procedure. total mass of J = Paper chromatography and gas / liquid chromatography both rely on the partition of compounds between mobile and stationary phases. Identify the mobile phase in paper chromatography. Suggest what type of liquid is used for the stationary phase in gas / liquid chromatography. Both these techniques can be used to separate mixtures. State what you would measure in order to distinguish between the components in the mixture in 1. paper chromatography, 2. gas / liquid chromatography. A mixture of three compounds was analysed by paper chromatography using a non-polar solvent. The resulting chromatogram is shown. mixture solvent front Identify which compound is responsible for each spot. compound spot CO2H CH2OH CO2H CO2H
9701_w14_qp_43
THEORY
2014
Paper 4, Variant 3
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Questions Discovered
112